Physics General Science Notes PDF

THE COMPLETE General Science Notes (Physics) for Railway Exams General Science - Physics S.No Contents Page Number 1 Units and Measurements 2...

THE COMPLETE General Science Notes (Physics) for Railway Exams General Science - Physics S.No Contents Page Number 1 Units and Measurements 2 2 Motion 9 3 Force and laws of motion 14 4 Gravitation 20 5 Works and energy 25 6 Sound 27 Page 1 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 7 Light 33 8 The human eye and the colourful world 40 9 Electricity 44 10 Sources of energy 51 11 Inventions and discoveries 54 12 Physics one liners 56 Units and Measurements UNIT A unit is defined as a standard or fixed quantity of one kind used to measure other quantities of the same kind  Fundamental units and derived units are the two classifications of units  Fundamental units: Quantities which cannot be expressed in terms of any other physical quantities are called fundamental quantities. The units used to measure the fundamental quantities are called fundamental units Example: Length, mass, time, temperature etc.  Derived units: Units which are derived from basic units and bear a constant relationship with fundamental units. Examples are area, volume, pressure, force, etc. INTERNATIONAL SYSTEM OF UNITS In earlier time scientists of different countries were using different systems of units for measurement. Three such systems are CGS, FPS and MKS. Base units for length, mass and time in these systems were as follows  FPS system: The basic units of length, mass and time are measured in foot, pound and second respectively  CGS system: The basic units of length, mass and time are measured in centimeter, gram and seconds respectively  MKS system: The basic units of length, mass and time are measured in metre, kilogram and second respectively  S.I. units are referred to as Systems International units Page 2 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams FUNDAMENT UNITS OF FPS, CGS, MKS AND SI UNITS S.No Basic FPS CGS MKS SI Units quantity 1 Length Foot Centimetre Metre Metre 2 Mass Pound Gram Kilogram Kilogram 3 Time Second Second Second Second 4 Current Ampere Ampere Ampere Ampere 5 Temperature Fahrenheit Centigrade Centigrade Kelvin 6 Light Candela Candela Candela Candela intensity SI BASE QUANTITIES AND UNITS  There are seven fundamental units in the SI system of units. They are also known as base units Quantity SI Unit Symbol Length Metre M Mass Kilogram Kg Time Second S Electric current Ampere A Thermo dynamic temperature Kelvin K Amount of substance Mole Mol Luminous intensity Candela Cd SI DERIVED UNITS Page 3 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams S.No Quantity SI Unit 1 Area Square metre 2 Volume Cubic metre 3 Velocity Metre/second 4 Acceleration Metre/second square 5 Density Kilogram/metre Cube 6 Work Joule 7 Energy Joule 8 Force Newton 9 Weight Newton 10 Pressure Pascal 11 Frequency Hertz 12 Power Watt 13 Impulse Newton-second 14 Angular velocity Radian /second 15 Electric charge Coulomb 16 Electric potential(voltage) Volt 17 Capacitance Farad 18 Inductance Henry 19 Resistance Ohm 20 Impedance Ohm Page 4 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 21 Reactance Ohm 22 Electrical conductance siemens 23 Magnetic flux Weber 24 Magnetic flux density Tesla 25 Heat Joule 26 Angle Radian 27 Radioactivity Becquerel 28 Luminous flux Lumen 29 Momentum kilogram meter per second 30 Torque Newton metre 31 Specific heat Joule per kilogram kelvin SI Prefixes Used with Units in Physics  Unit prefixes are the symbols placed before the symbol of a unit to specify the order of magnitude of the quantity. They are useful to express very large and very small quantities. k (kilo) is the unit prefix in the unit, kilometer. A unit prefix stands for a specific positive or negative power of 10 Name Factor Femto 10-15 Pico 10-12 Nano 10-9 Micro 10-6 Milli 10-3 Centi 10-2 Page 5 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Deci 10-1 Deka 10 Hector 102 Kilo 103 Mega 106 Giga 109 Tera 1012 Peta 1015 IMPORTANT POINTS  1 fermi = 10–15 m  1 angstrom = 1 Å = 10–10 m  Speed of the light in vacuum is 3.00 × 108 m/s  Astronomical unit (AU): It is the mean distance of the centre of the Sun from the centre of the Earth.  1 astronomical unit = 1.496 × 10^11 m  Light year is a unit of length used to express astronomical distances.  Light year=9.46 × 1015 m  Parsec: Parsec is the unit of distance used to measure astronomical objects outside the solar system.  1 Parsec = 3.08 × 1016 m  1 Parsec = 3.26 light year.  Time is a measure of duration of events and the intervals between them. The SI unit of time is second.  Heat is a form of energy. Temperature is the degree of hotness or coldness of a body. The relationship for conversion from one temperature scale to the others is  Mass: Mass is the quantity of matter contained in a body. The SI unit of mass is kilogram (kg). 1 g = 1/1000 × 1 kg = 0.001 kg 1 mg = 1/1000000 × 1 kg = 0.000001 kg 1 quintal = 100 × 1 kg = 100 kg Page 6 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 1 metric tonne = 1000 × 1 kg = 10 quintal  Mass of 1 ml of water = 1g Mass of 1l of water = 1kg Mass of the other liquids vary with their density.  Atomic mass unit: Mass of a proton, neutron and electron can be determined using atomic mass unit (amu). 1 amu = (1/12)th of the mass of C12 atom Measurement of length  Metre scale is used for lengths from 10–3 m to 102 m  Verniercalliper is used for lengths to an accuracy of 10–4 m  Screw gauge and a spherometer can be used to measure lengths as less as to 10–5m LIST OF SCIENTIFIC INSTRUMENTS AND THEIR USES S.No Instrument Uses 1 Altimeter Measures altitude. It‟s used in aircrafts 2 Ammeter Measures strength of electric current 3 Anemometer Used for measuring wind speed and direction 4 Audiometer Measures Intensity of Sound 5 Barograph Continuous recording of atmospheric pressure 6 Barometer Measures atmospheric pressure 7 Binoculars Optical instrument used for magnified view of distant object 8 Bolometer To measure heat Radiation 9 Callipers Measure diameter of thin cylinder or wire 10 Calorimeter Measures quantities of heat 11 Cardiogram Traces movements of the heart and recorded on a Cardiograph Page 7 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 12 Colorimeter Compares Intensity of colours 13 Commutator Used in generators to reverse the direction of electric current 14 Crescograph Used to measure the growth of plants 15 Cryometer Used to measure very low temperatures 16 Dynamometer Measures electrical power 17 Electroscope It detects presence of an electric charge 18 Endoscope To examine internal parts of the body 19 Fathometer Measure depth of the ocean 20 Galvanometer Measures electric current 21 Hydrometer Instrument used for measuring the relative density of liquids 22 Hygrometer It measures humidity of air 23 Hydrophone Measures sound under water 24 Lactometer It determines the purity of milk 25 Microscope To obtain a magnified view of small objects 26 Photometer The instrument Compares the luminous intensity of the source of light. 27 Pyrometer Measure very high temperature especially in furnaces and kilns 28 Odometer The instrument used for measuring the distance traveled by a vehicle such as a bicycle or car 29 Ohmmeter The electrical instrument that measures electrical resistance Page 8 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 30 Periscope It is used to view object above the sea level 31 Salinometer It determines the salinity of solutions 32 Sphygmometer It measures the blood pressure 33 Stroboscope To view rapidly moving objects 34 Seismograph The instrument used to detect and record earthquakes 35 Telescope Used for magnified view of distant objects 36 Spectrometer Properties of light MOTION  Motion is a change of position it can be described in terms of the distance moved or the displacement.  When a body does not change its position, with respect to its surroundings, it is said to be at rest. When a body changes its position, with respect to its surroundings, it is said to be in motion  The motion of an object could be uniform or non-uniform depending on whether its velocity is constant or changing.  Uniform motion: An object is said to be in uniform motion if it covers equal distances in equal intervals of time howsoever big or small these time intervals may be.  Non-uniform motion: An object is said to be in non-uniform motion if it covers unequal distances in equal intervals of time. Scalar and vector SCALAR VECTOR A scalar is a quantity with magnitude only A vector is a quantity with the magnitude as well as direction Page 9 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Examples are Length, Area, Distance, Speed, Examples are Displacement, Velocity, Mass, Density, Pressure, etc.. Acceleration, momentum, Force Distance and displacement  Distance The actual length of the path travelled by a moving body irrespective of the direction is called the distance travelled by the body. It is measured in metre in SI system. It is a scalar quantity having magnitude only.  Displacement: It is defined as the change in position of a moving body in a particular direction. It is a vector quantity having both magnitude and direction. It is also measured in metre in SI system. DISTANCE DISPLACEMENT Distance of the object can be defined as the Displacement of the object can be defined complete path travelled by on object as the overall motion of the object or during its motion minimum distance between the starting point of the object and the final position of the object Distance is a scalar quantity Displacement is a vector quantity Distance of the any object does not depend Displacement of the any object depends on on the direction of its motion the direction of its motion  Distance is refers to how much ground an object has covered during its motion(A - BC ) Distance=4+3=7  Displacement is a to refers to “how far out of place an object is(“AC ) Displacement=5  Distance gives the complete information about the path travelled by the object  Displacement does not gives the complete information about the path travelled by the object Page 10 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Speed, Velocity and Acceleration  Speed: Speed is the rate of change of distance or the distance travelled in unit time. It is a scalar quantity. Speed = Distance travelled / Time  Speed is scalar quantity and unit is m/s  Speed of objects help us to decide which one is moving faster than the other.  Velocity: Velocity is the rate of change of displacement. It is the displacement in unit time. It is a vector quantity. Velocity = Displacement / Time  Velocity is vector quantity and unit is m/s  During uniform motion of an object along a straight line, the velocity remains constant with time. In this case, the change in velocity of the object for any time interval is zero.  During non-uniform motion, velocity varies with time. It has different values at different instants and at different points of the path. Thus, the change in velocity of the object during any time interval is not zero. This phenomenon is called acceleration  Acceleration : Acceleration of an object is the change in velocity per unit time  Unit of acceleration is m/s2  Acceleration is vector quantity Acceleration= Change in velocity/time Acceleration= (Final velocity – Initial velocity)/Time a = (v–u) /t From the above equation 1. If v > u, i.e. if final velocity is greater than initial velocity, the velocity increases with time and the value of acceleration is positive. 2. If v < u, i.e. if final velocity is less than initial velocity, the velocity decreases with time and the value of acceleration is negative. It is called negative acceleration. Negative acceleration is called retardation or deceleration Graphical Representation of Motion  The distance – time graph for Uniform motion Page 11 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The distance time graph for Non-uniform motion  Velocity-time graph for a body having uniform acceleration The nature of the graph shows that velocity changes by equal amounts in equal intervals of time. Thus, for all uniformly accelerated motion, the velocity-time graph is a straight line. Page 12 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  In the case of non-uniformly accelerated motion, velocity-time graphs can have any shape. EQUATIONS OF MOTION  When an object moves along a straight line with uniform acceleration, it is possible to relate its velocity, acceleration during motion and the distance covered by it in a certain time interval by a set of equations known as the equations of motion. Such equations are v = u + at s = ut + ½ at2 2 a s = v2 – u2 Where u-is the initial velocity v-is the initial velocity a -Acceleration s- Displacement t=Time of motion MOTION OF FREELY FALLING BODY  When all objects are dropped in the absence of air medium (vacuum), all would have reached the ground at the same time.  In air medium, air offers some resistance to the motion of freely falling objects. But, it is negligibly small when compared to the gravitational pull. Hence, they reach the ground at the same time.  All Objects experiences acceleration during free fall. This acceleration experienced by an object is independent of mass. This means that all objects hollow or solid, big or small, should fall at the same rate.  The equation of motion for a freely falling body can be obtained by replacing „a‟ in equations with g, the acceleration due to gravity. For a freely falling body which is initially at rest, u = 0. Thus we get the following equations. v = gt s = ½ gt2 v2 = 2gh  When we throw an object vertically upwards, it moves against the acceleration due to gravity. Hence, „a‟ is taken to be –g and when moving downwards „a‟ is taken as +g UNIFORM CIRCULAR MOTION  If an object moves in a circular path with uniform speed, its motion is called uniform circular motion Page 13 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  There are many more familiar examples of objects moving under uniform circular motion, such as the motion of the moon and the earth, a satellite in a circular orbit around the earth, a cyclist on a circular track at constant speed and so on Important points  The state of motion of an object is described by its speed and the direction of motion. The state of rest is considered to be the state of zero speed. An object may be at rest or in motion both are its states of motion  When a body is thrown vertically upwards in space, at the highest point, the body has zero velocity but it has acceleration due to the gravity. FORCE AND LAWS OF MOTION FORCE  In science, a push or a pull on an object with mass that causes it to change velocity is called a force. Force has magnitude as well as direction  Force acting on an object may cause a change in its state of motion or a change in its shape  Forces applied on an object in the same direction add to one another  Forces act in the opposite directions on an object, the net force acting on it is the difference between the two forces  Balanced and unbalanced forces Balanced forces do not cause any change in motion whereas unbalanced forces does  Objects or things fall towards the earth because it pulls them. This force is called the force of gravity, or just gravity. This is an attractive force. The force of gravity acts on all objects. The force of gravity acts on all of us all the time without our being aware of it. Water begins to flow towards the ground as soon as we open a tap. Water in rivers flows downward due to the force of gravity. Gravity is not a property of the earth alone. In fact, every object in the universe, whether small or large, exerts a force on every other object. This force is known as the gravitational force.  Nuclear force is the strongest force in the nature  The force exerted by a charged body on another charged or uncharged body is known as electrostatic force. This force comes into play even when the bodies are not in contact  Body is said to be a equilibrium if sum of all the forces acts on the body is zero. In other words if it is at rest or moving with uniform velocity Page 14 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams State of Motion  The state of motion of an object is described by its speed and the direction of motion. The state of rest is considered to be the state of zero speed. An object may be at rest or in motion; both are its states of motion.  The force acting on a unit area of a surface is called pressure. Pressure = force / area on which it acts  Liquids and gases exert pressure on the walls of their containers.  The pressure exerted by air around us is known as atmospheric pressure. INERTIA  The inherent property of a body to resist any change in its state of rest or the state of uniform motion, unless it is influenced upon by an external unbalanced force, is known as „inertia‟. Types of Inertia Inertia of rest  The resistance of a body to change its state of rest is called inertia of rest  Example: When you vigorously shake the branches of a tree, some of the leaves and fruits are detached and they fall down Inertia of direction  The resistance of a body to change its direction of motion is called inertia of direction  Example: When you make a sharp turn while driving a car, you tend to lean sideways Inertia of motion  The resistance of a body to change its state of motion is called inertia of motion  Example: An athlete runs some distance before jumping. Because, this will help him jump longer and higher. LINEAR MOMENTUM  The product of mass and velocity of a moving body gives the magnitude of linear momentum. It acts in the direction of the velocity of the object. Linear Momentum = mass × velocity p = mv  Linear momentum is a vector quantity.  The linear momentum measures the impact of a force on a body. IMPULSE  When a force F acts on a body for a period of time t, then the product of force and time is known as „impulse‟ Impulse = F × t Page 15 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams NEWTON’S LAWS OF MOTION First Law of Motion  The first law of motion is stated as “An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force “  All objects resist a change in their state of motion. In a qualitative way, the tendency of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia. This is why, the first law of motion is also known as the law of inertia  Inertia is the natural tendency of an object to resist a change in its state of motion or of rest. The mass of an object is a measure of its inertia. Its SI unit is kilogram Galileo Galilei  Galileo Galilei was born on 15 February 1564 in Pisa, Italy. Galileo, right from his childhood, had interest in mathematics and natural philosophy. But his father Vincenzo Galilei wanted him to become a medical doctor. Accordingly, Galileo enrolled himself for a medical degree at the University of Pisa in 1581 which he never completed because of his real interest in mathematics. In 1586, he wrote his first scientific book „The Little Balance [La Balancitta]‟, in which he described Archimedes‟ method of finding the relative densities (or specific gravities) of substances using a balance.  In 1589, in his series of essays – De Motu, he presented his theories about falling objects using an inclined plane to slow down the rate of descent.  In 1592, he was appointed professor of mathematics at the University of Padua in the Republic of Venice. Here he continued his observations on the theory of motion and through his study of inclined planes and the pendulum, formulated the correct law for uniformly accelerated objects that the distance the object moves is proportional to the square of the time taken. Galileo was also a remarkable craftsman. He developed a series of telescopes whose optical performance was much better than that of other telescopes available during those days. Around 1640, he designed the first pendulum clock. In his book „Starry Messenger‟ on his astronomical discoveries, Galileo claimed to have seen mountains on the moon, the milky way made up of tiny stars, and four small bodies orbiting Jupiter. In his books „Discourse on Floating Bodies‟ and „Letters on the Sunspots‟, he disclosed his observations of sunspots. Using his own telescopes and through his observations on Saturn and Venus, Galileo argued that all the planets must orbit the Sun and not the earth, contrary to what was believed at that time. Second Law of Motion  The second law of motion states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force Page 16 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The SI unit of force is kg m s–2. This is also known as newton and represented by the symbol N. A force of one newton produces an acceleration of 1 m s–2 on an object of mass 1 kg  The second law of motion gives a method to measure the force acting on an object as a product of its mass and accelerations F=ma  The momentum, p of an object is defined as the product of its mass, m and velocity, v. That is p=mv  Momentum has both direction and magnitude. Its direction is the same as that of velocity, v. The SI unit of momentum is kilogram-metre per second  Real time example is a fielder pulls his hand backward while catching a cricket ball coming with a great speed to reduce the momentum of the ball with a little delay.In doing so the fielder increases the time during which the high velocity of the moving ball decreases to zero. Thus the acceleration of the ball is decreased and therefore the impact of catching the fast moving ball is also reduced  In a high jump athletic event the athletes are made to fall either on a cushioned bed or on a sand bed. This is to increase the time of the athlete‟s fall to stop after making the jump. This decreases the rate of change of momentum and hence the force. This prevents the athlete from getting hurt Third Law of Motion  The third law of motion states To every action, there is an equal and opposite reaction and they act on two different bodies  If a body A applies a force FA on a body B, then the body B reacts with force FB on the body A, which is equal to FA in magnitude, but opposite in direction. FB = –FAs Examples  Real time example is when a gun is fired it exerts a forward force on the bullet. The bullet exerts an equal and opposite force on the gun. This results in the recoil of the gun. Since the gun has a much greater mass than the bullet, the acceleration of the gun is much less than the acceleration of the bullet  Third law of motion is another example is when a sailor jumps out of a rowing boat. As the sailor jumps forward, the force on the boat moves it backwards  When birds fly they push the air downwards with their wings (Action) and the air pushes the bird upwards (Reaction).  Motion of rocket CONSERVATION OF MOMENTUM  Sum of momenta of the two objects before collision is equal to the sum of momenta after the collision provided there is no external unbalanced force acting on them. This is known as the law of conservation of momentum  In an isolated system (where there is no external force), the total momentum remains conserved Page 17 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams ROCKET PROPULSION  Propulsion of rockets is based on the law of conservation of linear momentum as well as Newton‟s third law of motion.  Rockets are filled with a fuel (either liquid or solid) in the propellant tank. When the rocket is fired, this fuel is burnt and a hot gas is ejected with a high speed from the nozzle of the rocket, producing a huge momentum. To balance this momentum, an equal and opposite reaction force is produced in the combustion chamber, which makes the rocket project forward PRESSURE  The effect of force can be measured using a physical quantity called pressure. It can be defined as the amount of force or thrust acting perpendicularly on a surface of area of one square meter of a body. Pressure = Thrust (or) Force/ Area The SI unit of pressure is pascal  Pressure exerted by a force depends on the magnitude of the force and the area of contact.  The effect of pressure can be increased by increasing the thrust or by decreasing the surface area of the body Atmospheric pressure  The amount of force or weight of the atmospheric air that acts downward on unit surface area of the surface of the Earth is known as atmospheric pressure.  It can be measured using the device called barometer.  The barometer was invented by Torricelli.  Atmospheric pressure decreases with altitude from the surface of the Earth. FRICTION  Frictional force or friction arises when two or more bodies in contact move or tend to move, relative to each other. It acts always in the opposite direction of the moving body. This force is produced due to the geometrical dissimilarities of the surface of the bodies, which are in relative motion  There are four types of friction: static, sliding, rolling, and fluid friction. Static, sliding, and rolling friction occur between solid surfaces. Fluid friction occurs in liquids and gases.  The frictional force exerted by fluids is also called drag.  Friction can be increased by increasing the area of the surfaces in contact  Friction depends on the nature of surfaces in contact.  Friction can produce the following effects. 1. Friction opposes motion. Page 18 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 2. It causes wear and tear of the surfaces in contact. 3. It produces heat. Increasing and Reducing Friction  The substances which reduce friction are called lubricants.  Friction can never be entirely eleminated. No surface is perfectly smooth. Some irregularities are always there. Advantages of Friction  We can hold objects in our hand due to friction.  We can walk on the road because of friction. The friction between footwear and the ground help us to walk without slipping.  Writing on the paper with a pen is easy due to friction.  Automobiles can move safely due to friction between the tyres and the road. Brakes can be applied due to frictional resistance on brake shoes. Spring Balance  Spring balance is a device used for measuring the force acting on an object. It consists of a coiled spring which gets stretched when a force is applied to it. Stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force GRAVITATION All objects in the universe attract each other. This force of attraction between objects is called the gravitational force. Gravitation is a weak force unless large masses are involved Centripetal force  The force that causes acceleration and keeps the body moving along the circular path is acting towards the Centre. This force is called the centripetal („Centreseeking‟) force  The motion of the moon around the earth is due to the centripetal force. If there were no such force the moon would pursue a uniform straight line motion. Centrifugal force  The force that is felt by an object moving in a curved path that acts outwardly away from the center of rotation  Centrifugal force acts in a direction which is opposite to the direction of the centripetal force.  Some of the applications of centrifugal force Page 19 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams 1. Banking of roads. 2. Washing machine dryer. 3. Cream separator. UNIVERSAL LAW OF GRAVITATION Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. G Universal gravitation constant G6.673 *10–11 N m2 kg–2  The value of G was found out by Henry Cavendish (1731 – 1810) by using a sensitive balance  The force exerted by the earth on the moon is 2.02 *1020 N  Newton's law of gravitation is called universal law of gravitation because it is applicable to all the bodies having mass whether the bodies are big or small or whether the bodies are terrestrial or celestial Isaac Newton  Isaac Newton was born in Woolsthorpe near Grantham, England. He is generally regarded as the most original and influential theorist in the history of science.  Newton formulated the well-known laws of motion. He worked on theories of light and colour. He designed an astronomical telescope to carry out astronomical observations. Newton was also a great mathematician. He invented a new branch of mathematics, called calculus. He used it to prove that for objects outside a sphere of uniform density, the sphere behaves as if the whole of its mass is concentrated at its centre.  Newton transformed the structure of physical science with his three laws of motion and the universal law of gravitation. As the keystone of the scientific revolution of the seventeenth century, Newton‟s work combined the contributions of Copernicus, Kepler, Galileo, and others into a new powerful synthesis. IMPORTANCE OF THE UNIVERSAL LAW OF GRAVITATION  The force that binds us to the earth.  The motion of the moon around the earth.  The motion of planets around the Sun.  The tides due to the moon and the Sun. Page 20 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Acceleration due to gravity  Whenever an object falls towards the earth acceleration is involved. This acceleration is due to the earth‟s gravitational force. Therefore this acceleration is called the acceleration due to the gravitational force of the earth or acceleration due to gravity g=GM/R2 G = 6.7 × 10–11 N m2 kg-2, Mass of the earth M= 6 × 1024 kg Radius of the earth R= 6.4 × 106 m. From the equation we get g value  Value of acceleration due to gravity of the earth, g = 9.8 m/s2  The earth is not a perfect sphere. The radius of the earth increases from the poles to the equator because value of g becomes greater at the poles than at the equator.  Value of g decreases with the increase of height  Value of g decreases with depth and become zero at the center of the earth  Acceleration experienced by an object is independent of its mass. It means that all objects hollow or solid, big or small, should fall at the same rate Mass of the Earth  Mass of the Earth M = g R2 /G Substituting the known values of g, R and G, you can calculate the mass of the Earth as M = 5.972 × 1024 kg MASS  The Mass is a measure of the amount of matter in an object and it is a scalar quantity and its SI unit is kilograms  It remains the same whether the object is on the earth the moon or even in outer space  The mass of an object is constant and does not change from place to place WEIGHT  The earth attracts every object with a certain force and this force depends on the mass (m) of the object and the acceleration due to the gravity (g)  The weight of an object is the force with which it is attracted towards the earth W=mg  The SI unit of weight is the same as that of force that is newton (N) and weight is a vector quantity  Weight depends on its location because g depends on location Page 21 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Acceleration due to gravity of the moon is less than the acceleration due to gravity of the earth because Weight of the object on the moon1/6th of its weight on the earth  The weight of an object is directly proportional to its mass W∝m APPARENT WEIGHT  The weight that you feel to possess during up and down motion is not same as your actual weight. Apparent weight is the weight of the body acquired due to the action of gravity and other external forces acting on the body.  Different possibilities of the apparent weight of the person that arise, depending on the motion of the lift 1. Lift is moving upward with acceleration  Apparent weight is greater than the actual weight. 2. Lift is moving downward with acceleration  Apparent weight is lesser than the actual weight. 3. Lift is at restApparent weight is equal to the actual weight. 4. Lift is falling down freely Apparent weight is equal to zero. THRUST AND PRESSURE  The force acting on an object perpendicular to the surface is called thrust.  In SI units, the unit of thrust is newton (denoted as N)  The force per unit area acting on an object concerned is called pressure. We can say thrust on a unit area is pressure. Pressure = Thrust /Area  The unit of pressure is newton per square metre or newton metre–2 (denoted as Nm–2)  1 newton per square metre is called as 1 pascal PRESSURE IN FLUIDS  All liquids and gases are fluids.  A solid exerts pressure on a surface due to its weight. Similarly, fluids have weight, and they also exert pressure on the base and walls of the container in which they are enclosed. Pressure exerted in any confined mass of fluid is transmitted undiminished in all directions. Buoyancy  Buoyancy is the force exerted on an object that is wholly or partly immersed in a fluid  All objects experience a force of buoyancy when they are immersed in a fluid  The magnitude of this buoyant force depends on the density of the fluid  Salt water provides more buoyant force than fresh water, because, buoyant force depends as much on the density of fluids as on the volume displaced. Page 22 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Archimedes’ Principle  Archimedes principle states that „a body immersed in a fluid experiences a vertical upward buoyant force equal to the weight of the fluid it displaces’  Archimedes principle has many applications  It is used in designing ships and submarines  Lactometers which are used to determine the purity of a sample of milk  Hydrometers used for determining density of liquids Archimedes  Archimedes was a Greek scientist. He discovered the principle, subsequently named after him, after noticing that the water in a bathtub overflowed when he stepped into it. He ran through the streets shouting “Eureka!”, which means “I have got it”. This knowledge helped him to determine the purity of the gold in the crown made for the king.  His work in the field of Geometry and Mechanics made him famous. His understanding of levers, pulleys, wheels and-axle helped the Greek army in its war with Roman army. Relative Density  The density of a substance is defined as mass of a unit volume. The unit of density is kilogram per metre cube  The density of a given sample of a substance can help us to determine its purity.  Objects having density less than that of the liquid in which they are immersed float on the surface of the liquid  Density of the object is more than the density of the liquid in which it is immersed then it sinks in the liquid  The relative density of a substance is the ratio of its density to that of water Relative density=Density of a substance/Density of water Since the relative density is a ratio of similar quantities, it has no unit. Pascal’s law  Pascal‟s law states that an increase in pressure at any point inside a liquid at rest is transmitted equally and without any change, in all directions to every other point in the liquid. The applications of Pascal’s law are:  In automobile service stations, the vehicles are lifted upward using the hydraulic lift which works as per Pascal‟s law.  Automobile brake system works according to Pascal‟s law.  The hydraulic press is used to compress the bundles of cotton or cloth so as to occupy less space. Page 23 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Surface Tension  Surface tension is the property of a liquid. The molecules of a liquid experience a force, which contracts the extent of their surface area as much as possible, so as to have the minimum value. The amount of force acting per unit length, on the surface of a liquid is defined as surface tension.  Its unit is Nm–1.  Surface tension is the reason for many events we see in our daily life. 1. In plants, water molecules rise up due to surface tension. Xylem tissues are very narrow vessels present in plants. Water molecules are absorbed by the roots and these vessels help the water to rise upward due to 'capillarity action', which is caused by the surface tension of water. 2. During heavy storm, ships are damaged due surface tension of water. By pouring oil or soap powder into the sea, sailors reduce its impact. 3. Water strider insect slides on the water surface easily due to the surface tension of water 4. A falling drop of rain water acquires the spherical shape due to Surface Tension Viscosity  The frictional force acting between the successive layers of the liquid which acts in order to oppose the relative motion of the layer is known as viscous force. Such a property of a liquid is called viscosity. WORK AND ENERGY WORK  We define work to be equal to the product of the force and displacement Work done = force * displacement  Work done by force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction  Unit of work is newton metre (N m) or joule (J)  Work done on an object by a force would be zero if the displacement of the object is zero  The work done by a force can be either positive or negative  Work done is negative when the force acts opposite to the direction of displacement.  Work done is positive when the force is in the direction of displacement  When a body falls freely under gravity then the work done by the gravity is positive Explanation is If a force acting on a body has a component in the direction of displacement then the work done by the force is positive because when a body falls freely under the influence of gravity the work done by the gravity is positive Page 24 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  When a body slides against a rough horizontal surface the work done by friction is negative Explanation is When a body slides against a rough horizontal surface its displacement is opposite to that of the force of friction so the works done by the friction is negative ENERGY  Life is impossible without energy  An object having capability to do work is said to possess energy  Unit of energy is joule. Joule is also unit of work  Various form of energy are Mechanical energy, Electrical energy, Atomic energy, Heat energy, Light energy, Chemical energy and sound energy.  Energy of one form can be transformed into energy of another form  The sum of the kinetic and potential energies of an object is called its mechanical energy James Prescott Joule  James Prescott Joule was an outstanding British physicist. He is best known for his research in electricity and thermodynamics. Amongst other things, he formulated a law for the heating effect of electric current. He also verified experimentally the law of conservation of energy and discovered the value of the mechanical equivalent of heat. The unit of energy and work called joule, is named after him. KINETIC ENERGY  Kinetic energy is the energy possessed by an object due to its motion  The kinetic energy of an object increases with its Speed  Example of kinetic energy are Falling coconut, a speeding car, a rolling stone, a flying aircraft, flowing water, blowing wind, a running athlete etc.  The kinetic energy of a body moving with a certain velocity is equal to the work done on it to make it acquire that velocity  An object of mass (m) moving with velocity (v) has a kinetic energy of POTENTIAL ENERGY Page 25 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The energy possessed by a body due to its change in position or shape is called the potential energy  The potential energy possessed by the object is the energy present in it by virtue of its position or configuration  An object increases its energy when raised through a height. This is because work is done on it against gravity while it is being raised. The energy present in such an object is the gravitational potential energy.  The gravitational potential energy of an object at a point above the ground is defined as the work done in raising it from the ground to that point against gravity  The gravitational potential energy of an object of mass (m) raised through a height ( h) from the earth‟s surface is given by = m g h.  The work done by gravity depends on the difference in vertical heights of the initial and final positions of the object and not on the path along which the object is moved LAW OF CONSERVATION OF ENERGY According to the law of conservation of energy  The energy can neither be created nor destroyed.  Energy can only be transformed from one form to another.  The total energy before and after the transformation always remains constant  An object of mass (m) is made to fall freely from a height (h). At the start, the potential energy is mgh and kinetic energy is zero. Why is the kinetic energy zero. It is zero because its velocity is zero. The total energy of the object is thus mgh. As it falls its potential energy will change into kinetic energy. If v is the velocity of the object at a given instant the kinetic energy would be ½mv^2. As the fall of the object continues, the potential energy would decrease while the kinetic energy would increase. When the object is about to reach the ground, h = 0 and v will be the highest. Therefore, the kinetic energy would be the largest and potential energy the least. However, the sum of the potential energy and kinetic energy of the object would be the same at all points Potential energy + kinetic energy = constant  The sum of kinetic energy and potential energy of an object is its total mechanical energy Rate of Doing Work  Power is defined as the rate of doing work or the rate of transfer of energy Power = work/time  Unit of power is watt  1 watt = 1 joule/second or 1 W = 1 J s–1  The unit joule is too small and hence is inconvenient to express large quantities of energy. We use a bigger unit of energy called kilowatt hour  1 kW h = 3.6 * 106 J Page 26 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The energy used in households, industries and commercial establishments are usually expressed in kilowatt hour. SOUND  Sound is a form of energy which produces a sensation of hearing in our ears. There are also other forms of energy like mechanical energy, light energy, etc.  Sound is produced due to vibration of different objects  Sound waves are longitudinal mechanical waves  Sound waves are characterized by the motion of particles in the medium and are called mechanical waves.  The sound of the human voice is produced due to vibrations in the vocal cords. The vocal cords in men are about 20 mm long. In women these are about 15mm long. Children have very short vocal cords. This is the reason why the voices of men, women and children are different.  The eardrum senses the vibrations of sound it sends the signals to the brain. This process is called hearing.  The eardrum is like a stretched rubber sheet.  The outer ear is called pinna Its collects the sound from the surroundings  The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. SOUND NEEDS A MEDIUM TO TRAVEL  Sound is a mechanical wave and needs a material medium like air, water, steel etc.  Sound cannot travel through vacuum CHARACTERISTICS OF A SOUND WAVE Sound wave describe its  Frequency  Amplitude  Speed FREQUENCY  The distance between two consecutive compressions or two consecutive rarefactions is called the wavelength. Its SI unit is metre.  The number of such oscillations per unit time is the frequency of the sound wave.SI unit is hertz Page 27 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Human ear can hear sound of frequency from 20 Hz to 20,000 Hz. Sound with frequency less than 20 Hz is called infrasonic sound. Sound with frequency greater than 20,000 Hz is called ultrasonic sound. Human beings cannot hear infrasonic and ultrasonic sounds.  Time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave.SI unit is second.  Frequency and time period are reciprocal to each other.  Relationship between frequency and time period is.  The sensation of frequency commonly referred as the pitch of a sound. Objects of different sizes and conditions vibrate at different frequencies to produce sounds of different pitch.  The frequency determines the shrillness or pitch of a sound. If the frequency of vibration is higher we say that the sound is shrill and has a higher pitch. If the frequency of vibration is lower, we say that the sound has a lower pitch.  A sound of single frequency is called a tone.  When sound waves move from one medium to another medium its wavelength and speed changes but frequency remains unchanged. Heinrich Rudolph Hertz  Heinrich Rudolph Hertz was born on 22 February 1857 in Hamburg, Germany and educated at the University of Berlin. He confirmed J.C. Maxwell‟s electromagnetic theory by his experiments. He laid the foundation for future development of radio, telephone, telegraph and even television. He also discovered the photoelectric effect which was later explained by Albert Einstein. The SI unit of frequency was named as hertz in his honour. AMPLITUDE  Magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave.  The loudness or softness of a sound is determined basically by its amplitude. If the vibration of a particle has large amplitude, the sound will be loud and if the vibration has small amplitude, the sound will be soft  The amplitude of the sound wave depends upon the force with which an object is made to vibrate. If we strike a table lightly, we hear a soft sound because we produce a sound wave of less energy (amplitude).  Sound wave source moves away from the source its amplitude as well as its loudness decreases. Louder sound can travel a larger distance as it is associated with higher energy Page 28 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. For example, if the amplitude becomes twice, the loudness increases by a factor of 4. The loudness is expressed in a unit called decibel (dB). SPEED  Speed of sound is defined as the distance which a point on a wave such as a compression or a rarefaction travels per unit time Speed=distance/time  The speed of sound remains almost the same for all frequencies in a given medium under the same physical conditions  Amount of sound energy passing each second through unit area is called the intensity of sound  The speed of sound decreases when we go from solid to gaseous state. Speed of the sound maximum in solid state and minimum in gaseous state.  The speed of the sound remains unchanged by the increase or decrease of pressure.  The speed of sound in a medium depends on temperature of the medium. In any medium as we increase the temperature the speed of sound increases  Speed of sound is more in humid air than dry air because density of humid air is less than dry air  The speed of sound depends on the properties of the medium through which it travels  The sound of thunder is heard a little later than the flash of light is seen. So, we can make out that sound travels with a speed which is much less than the speed of light.  Sound travels about 5 times faster in water than in air. Since the speed of sound in sea water is very large.  Speed of sound in different medium Substance Speed m/s Aluminium 6420 Nickel 6040 Steel 5960 Iron 5950 Brass 4700 Glass 3980 Water(sea) 1531 Water(distilled) 1498 Ethanol 1207 Methanol 1103 Page 29 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams Hydrogen 1284 Helium 965 Air 346 Oxygen 316 Sulphur dioxide 213 SONIC BOOM  When the speed of any object exceeds the speed of sound it is said to be travelling at supersonic speed. Bullets, jet aircrafts etc. often travel at supersonic speeds. When a sound, producing source moves with a speed higher than that of sound, it produces shock waves in air. These shock waves carry a large amount of energy. The air pressure variation associated with this type of shock waves produces a very sharp and loud sound called the “sonic boom”. The shock waves produced by a supersonic aircraft have enough energy to shatter window glass and even damage buildings. REFLECTION OF SOUND  Sound bounces off a surface of solid or a liquid medium like a rubber ball that bounces off from a wall.  An obstacle of large size which may be polished or rough is needed for the reflection of sound waves.  The laws of reflection are: 1. The angle in which the sound is incident is equal to the angle in which it is reflected. 2. Direction of incident sound, the reflected sound and the normal are in the same plane. ECHO  We will hear the same sound again a little later due to the reflection of sound wave is called echo  To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s  The total distance covered by the sound from the point of generation to the reflecting surface and back should be at least 340 ms–1 × 0.1 s = 34 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance i.e. 17 m. This distance will change with the temperature of air. Echoes may be heard more than once due to successive or multiple reflections REVERBERATION  The repeated reflection that results in this persistence of sound is called reverberation  A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible. The repeated reflection that results in this persistence of sound is called reverberation. USES OF MULTIPLE REFLECTION OF SOUND Page 30 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Megaphones or loudhailers, horns, musical instruments such as trumpets and shehanais are all designed to send sound in a particular direction without spreading it in all directions  Stethoscope is a medical instrument used for listening to sounds produced within the body, mainly in the heart or lungs.  The ceilings of concert halls conference halls and cinema halls are curved so that sound after reflection reaches all corners of the hall RANGE OF HEARING  The audible range of hearing for average human beings is in the frequency range of 20 Hz – 20 kHz  Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound  Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound INFRASONIC SOUND  Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound  Rhinoceroses communicate using infrasound of frequency as low as 5 Hz  Whales and elephants produce sound in the infrasound range  Earthquakes produce low-frequency infrasound before the main shock waves begin which possibly alert the animals ULTRASONIC SOUND  Ultrasonic sound is the term used for sound waves with frequencies greater than 20,000Hz. These waves cannot be heard by the human ear, but the audible frequency range for other animals includes ultrasound frequencies. For example, dogs can hear ultrasonic sound.. APPLICATIONS OF ULTRASOUND  Ultrasounds can be used to detect cracks and flaws in metal blocks  Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called echocardiography.  Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of the human body.  Ultrasound may be employed to break small stones formed in the kidneys into fine grains  Ultrasounds can be used in cleaning technology. Minute foreign particles can be removed from objects placed in a liquid bath through which ultrasound is passed.  Porpoises use ultrasound for navigation and location of food in the dark SONAR Page 31 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  SONAR stands for Sound Navigation And Ranging  Sonar is a device that uses ultrasonic waves to measure the distance ,direction and speed of underwater objects  Sonar consists of a transmitter and a detector and is installed at the bottom of boats and ships.  The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound STRUCTURE OF HUMAN EAR  The outer ear is called „pinna’. It collects the sound from the surroundings. The collected sound passes through the auditory canal.  At the end of the ear is eardrum or tympanic membrane. When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones (the hammer, anvil and stirrup) in the middle ear.  The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear.  In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve and the brain interrupts them as sound. Noise Pollution  Unpleasant sounds are called noise.  Excessive or unwanted sounds lead to noise pollution. Noise pollution may pose health problems for human beings.  Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution.  Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc.  Plantation on the roadside and elsewhere can reduce noise pollution. LIGHT LIGHT-REFLECTION AND REFRACTION Page 32 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Light is a radiation which makes our eyes able to see the object when light from an object enters our eyes that we see the object. The light may have been emitted by the object, or may have been reflected by it  Light wave is an electromagnetic wave. It has an electric and a magnetic component  Light is a transverse wave  Light seems to travel in straight lines  Opaque objects do not allow light to pass through them  Transparent objects allow light to pass through them and we can see through these objects clearly  Translucent objects allow light to pass through them partially The materials through which objects can be seen, but not clearly, are known as translucent. Substances or materials, through which things can be seen, are called transparent. Glass, water, air and some plastics are examples of transparent materials.  Shadows are formed when an opaque object comes in the path of light  Light travels in vacuum with an enormous speed of 3×108 m s-1. The speed of light is different in different media  Sun light is white colour  Sunlight takes an average of 8 minutes and 20 seconds to travel from the Sun to the Earth  White light is composed of seven colours.  Splitting of light into its constituent colours is known as dispersion  Light is reflected from all surfaces  Any polished or a shining surface acts as a mirror  An image which can be obtained on a screen is called a real image  An image which cannot be obtained on a screen is called a virtual image  The image formed by a plane mirror is erect. It is virtual and is of the same size as the object. The image is at the same distance behind the mirror as the object is in front of it  In an image formed by a mirror, the left side of the object is seen on the right side in the image, and right side of the object appears to be on the left side in the image  Visually impaired persons can read and write using the Braille system  Beautiful patterns are formed in a kaleidoscope because of multiple reflections  Periscope works on the Laws of Reflection. Periscopes are used in submarines, tanks and also by soldiers in bunkers to see things outside REFLECTION  A highly polished surface such as a mirror reflects most of the light falling on it. Page 33 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Mirror changes the direction of light that falls on it. This change of direction by a mirror is called reflection of light.  Any polished or a shiny surface can act as a mirror.  Example a shining stainless steel plate or a shining steel spoon can change the direction of light. The surface of water can also act like a mirror and change the path of light.  Image formed by a plane mirror is always virtual and erect  The size of the image is equal to that of the object  Want to see full image in a plane mirror a person required a mirror of at least half the object  Lateral inversion is a phenomenon of the mirror in which the left of the object appears on the right and the right appears on the left.  Image formed in a plane mirror undergoes lateral inversion. LAWS OF REFLECTION  After striking the mirror the ray of light is reflected in another direction. The light ray which strikes any surface is called the incident ray  The ray that comes back from the surface after reflection is known as the reflected ray  Two laws of reflection are 1. The angle of incidence is equal to the angle of reflection. 2. Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane  These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces Nearly everything we see around is seen due to reflected light. Moon, for example, receives light from the Sun and reflects it. That‟s how we see the moon. The objects which shine in the light of other objects are called illuminated objects. There are other objects, which give their own light, such as the Sun, fire, flame of a candle and an electric lamp. Their light falls on our eyes. That is how we see them. The objects which emit their own light are known as luminous objects. OPTICAL DENSITY  The ability of a medium to refract light is also expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density.  Denser medium means optically denser medium and rarer medium means optically rarer medium.  In comparing two media, the one with the larger refractive index is optically denser medium than the other. The other medium of lower refractive index is optically rarer. The speed of light is higher in a rarer medium Page 34 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams than a denser medium. Thus, a ray of light travelling from a rarer medium to a denser medium slows down and bends towards the normal. When it travels from a denser medium to a rarer medium, it speeds up and bends away from the normal. SPHERICAL MIRROR  The reflecting surface of a spherical mirror may be curved inwards or outwards  A spherical mirror whose reflecting surface is curved inwards that is faces towards the center of the sphere is called a concave mirror  A spherical mirror whose reflecting surface is curved outwards is called a convex mirror CONCAVE MIRROR CONVEX MIRROR  Distance between the pole and the principal focus of a spherical mirror is called the focal length  Radius of curvature is found to be equal to twice the focal length  The centre of the reflecting surface of a spherical mirror is a point called the pole. Page 35 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams IMAGE FORMATION BY A CONCAVE MIRROR FOR DIFFERENT POSITIONS OF THE OBJECT Position of the Position of the Size of the image Nature of the image object image At infinity At the focus Highly diminished Real and inverted Beyond center of Between focus and Diminished Real and inverted curvature center of curvature At center of curvature At center of curvature Same size Real and inverted Between center of Beyond center of Enlarged Real and inverted curvature and focus curvature At focus At infinity Highly enlarged Real and inverted Between pole and Behind the mirror Enlarged Virtual and erect Focus NATURE POSITION AND RELATIVE SIZE OF THE IMAGE FORMED BY A CONVEX MIRROR Position of the object Position of the image Size of the image Nature of the image At infinity At the focus Focus Highly diminished Virtual and erect behind the mirror Between infinity Between pole and Focus Diminished Virtual and erect and the pole of the mirror behind the mirror USES OF CONCAVE MIRRORS  Concave mirrors are used in torches, search-lights and vehicles headlights to get powerful parallel beams of light.  Used as a shaving mirrors to see a larger image of the face.  Dentists use concave mirrors to see large images of the teeth of patients.  Concave mirrors are used to concentrate sunlight to produce heat in solar furnaces USES OF CONVEX MIRRORS  Convex mirrors are commonly used as rear view mirrors in vehicles Page 36 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Convex mirrors are installed on public roads as traffic safety device. They are used in acute bends of narrow roads such as hairpin bends in mountain passes where direct view of oncoming vehicles is restricted MIRROR FORMULA The relationship between the object-distance (u), image-distance (v), and focal length (f) of a spherical mirror given by the mirror formula which is expressed as MAGNIFICATION Magnification is expressed as the ratio of the height of the image to the height of the Object REFRACTION OF LIGHT  Refraction of light is the change in direction of a light ray when it travels from one medium to another  This deviation (change in direction) in the path of light is due to the change in velocity of light in the different medium  Velocity of light is more in a rarer medium (low optical density) than in a denser medium (high optical density).  Light does not travel in the same direction in all media. It appears that when travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as refraction of light  The coin becomes visible on pouring water into the bowl. The coin appears slightly raised above its actual position due to refraction of light.  Lemon kept in water in a glass tumbler appears to be bigger than its actual size, when viewed from the sides due to refraction of light  When a ray of light enter one medium to another medium its phase and frequency do not change but wavelength and velocity change LAWS OF REFRACTION OF LIGHT  Following are the laws of refraction of light. Page 37 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.  The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell‟s law of refraction. (This is true for angle 0 90º refraction is impossible and the ray is totally reflected back to the same medium (denser medium). This is called as total internal reflection.  Conditions to achieve total internal reflection 1. Light must travel from denser medium to rarer medium. (Example: From water to air). „ 2. The angle of incidence inside the denser medium must be greater than that of the critical angle. Examples of Total Internal Reflection  Optical fibres work on the phenomenon of total internal reflection  Mirage  Total internal reflection is the main cause for the spectacular brilliance of diamonds Braille System  The most popular resource for visually challenged persons is Braille.  Louis Braille, himself a visually challenged person, developed a system for visually challenged persons and published it in 1821. Page 39 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The present system was adopted in 1932. There is Braille code for common languages, mathematics and scientific notation. Many Indian languages can be read using the Braille system.  Braille system has 63 dot patterns or characters. Each character represents a letter, a combination of letters, a common word or a grammatical sign. Dots are arranged in cells of two vertical rows of three dots each.  Lal Advani, himself visually impaired, established an Association for special education and rehabilitation of disabled in India. Besides this, he represented India on Braille problems in UNESCO.  Helen A. Keller, an American author and lecturer, is perhaps the most wellknown and inspiring visually challenged person. She lost her sight when she was only 18 months old. But because of her resolve and courage she could complete her graduation from a university. She wrote a number of books including The Story of my Life (1903). THE HUMAN EYE AND THE COLOURFUL WORLD  Human eye is one of the most valuable and sensitive sense organs  Light enters the eye through a thin membrane called the cornea  Retina is lens system forms an image on a light-sensitive screen  The human eye forms the image of an object at its retina  The retina contains several nerve cells. Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve. There are two kinds of cells– (i) cones, which are sensitive to bright light and (ii) rods, which are sensitive to dim light. Cones sense colour. At the junction of the optic nerve and the retina, there are no sensory cells, so no vision is possible at that spot. This is called the blind spot.  The impression of an image does not vanish immediately from the retina. It persists there for about 1/16th of a second. So, if still images of a moving object are flashed on the eye at a rate faster than 16 per second, then the eye perceives this object as moving.  Iris is colored part of the eye. It may be blue, brown or green in colour. Every person has a unique colour, pattern and texture. It holds the pupil and also adjust the size of pupil according to the intensity of light  Pupil is black in color and absorbs all the light rays falling on it. It gets constricted when the intensity of light is high. It gets expanded when the intensity of light is low  Pupil is the centre part of the Iris. It is the pathway for the light to retina.  Ciliary muscles hold the lens. They adjust the focal length of the lens  Eye Lens is the important part of human eye. It is convex in nature. Page 40 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The ability of the eye to focus on both near and distant objects by adjusting its focal length is called the accommodation of the eye  The eye lens forms an inverted real image of the object on the retina. The retina is a delicate membrane having enormous number of light-sensitive cells. The light-sensitive cells get activated upon illumination and generate electrical signals. These signals are sent to the brain via the optic nerves. The smallest distance at which the eye can see objects clearly without strain is called the near point of the eye or the least distance of distinct vision. For a young adult with normal vision it is about 25 cm.  The farthest point up to which the eye can see objects clearly is called the far point of the eye. It is infinity for a normal eye  The crystalline lens of people at old age becomes milky and cloudy. This condition is called cataract. This causes partial or complete loss of vision. It is possible to restore vision through a cataract surgery. Two eyes for vision  There are several advantages of our having two eyes instead of one. It gives a wider field of view. A human being has a horizontal field of view of about 150° with one eye and of about 180° with two eyes. The ability to detect faint objects is, of course, enhanced with two detectors instead of one. DEFECTS OF VISION AND THEIR CORRECTION  A normal human eye can clearly see all the objects placed between 25cm and infinity. But, for some people, the eye loses its power of accommodation. This could happen due to many reasons including ageing. Hence, their vision becomes defective. Let us discuss some of the common defects of human eye.  There are mainly three common refractive defects of vision  Myopia or near-sightedness  Hypermetropia or farsightedness,  Presbyopia MYOPIA  Myopia is also known as near-sightedness  A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.  The focal length of eye lens is reduced or the distance between eye lens and retina increases.  In a myopic eye the image of a distant object is formed in front of the retina  A concave lens of suitable power will bring the image back on to the retina and thus the defect is corrected HYPERMETROPIA  Hypermetropia is also known as far-sightedness  A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly Page 41 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  The focal length of eye lens is increased or the distance between eye lens and retina decreases. Hence, the near point will not be at 25cm for such eyes and the near point has moved farther. Due to this, the image of nearby objects are formed behind the retina  In a hypermetropia eye the image of a closeby object are focused at a point behind the retina  This defect can be corrected by using a convex lens of appropriate power PRESBYOPIA  The power of accommodation of the eye usually decreases with ageing  It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens  This defect can be corrected by using a bi-focal lenses  A common type of bi-focal lenses consists of both concave and convex lenses. The upper portion consists of a concave lens.It facilitates distant vision. The lower part is a convex lens. It facilitates near vision. ASTIGMATISM  In this defect, eye cannot see parallel and horizontal lines clearly. It may be inherited or acquired. It is due to the imperfect structure of eye lens because of the development of cataract on the lens, ulceration of cornea, injury to the refracting surfaces, etc. Astigmatism can be corrected by using cylindrical lenses.  Animals have eyes shaped in different ways. Eyes of a crab are quite small but they enable the crab to look all around. So, the crab can sense even if the enemy approaches from behind. Butterflies have large eyes that seem to be made up of thousands of little eyes. They can see not only in the front and the sides but the back as well.  A night bird (owl) can see very well in the night but not during the day. On the other hand, day light birds (kite, eagle) can see well during the day but not in the night. The owl has a large cornea and a large pupil to allow more light in its eye. Also, it has on its retina a large number of rods and only a few cones. The day birds on the other hand, have more cones and fewer rods. DISPERSION OF WHITE LIGHT BY A GLASS PRISM  The angle between its two lateral faces is called the angle of the prism  The prism has probably split the incident white light into a band of colours  The various colours seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red  The band of the coloured components of a light beam is called its spectrum  The splitting of light into its component colours is called dispersion Page 42 of 60 Get High Standard Mock Test Series for all Bank Exams If there are any suggestions/ errors in our PDFs Feel Free to contact us via this email: [email protected]  THE COMPLETE General Science Notes (Physics) for Railway Exams  Isaac Newton was the first to use a glass prism to obtain the spectrum of sunlight.  Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. The red light bends the least while the violet the most  Red light has the longest wave