Physics Notes PDF

Unit 1: 1. Trundle wheel is used to measure lengths of tens of metres 2. Standard human reaction time for an alert person is 0.25s 3. Multiple readings are taken to reduce uncertainty in measurements and increase accuracy 4. Velocity is the displacement of an object per unit time/ speed in a given direction 5. Electric field strength is a vector quantity 6. Power is a scalar quantity 7. An object can change its velocity in several ways: a. Speeding up b. Slowing down c. Changing direction 8. If an object is accelerating, the distance time graph will be a curved line 9. When acceleration is increasing the speed time graph is a curve: a. Velocity is increasing at an increasing rate, i.e. the speed changes by the same amount in increasingly shorter time intervals 10. In the absence of air resistance, all objects fall with the same acceleration regardless of mass: acceleration of freefall 11. Objects falling through a vacuum will never reach terminal velocity 12. Air resistance is a frictional force produced by collisions with air particles as the object moves through the air 13. Mass is a measure of the quantity of matter in an object at rest relative to the observer 14. Mass resists change in motion 15. Gravitational field strength is the force per unit mass acting on an object in an gravitational field 16. Measurement apparatus + resolutions: a. Vernier caliper (0.01 mm): to measure objects to around 15 cm in length b. Micrometer (0.001 mm): to measure objects to around 3 cm in length c. Digital balance (0.01 g) and 30 cm ruler (1 mm) d. Pointer: to accurately read extension from ruler 17. Upthrust is a force that pushes upwards on an object immersed in a fluid a. upthrust= weight: float b. upthrust < weight: sink 18. Forces can change: a. Speed b. Direction c. Shape d. Size 19. Resultant force: single force that describes all of the forces acting on a body 20. Stiff springs have a large spring constant, stretchy springs have a small spring constant 21. The force needed to make something follow a circular path depends on a number of factors: a. The mass of the object: a greater mass requires a greater force when the speed and radius are constant b. The speed of the object: a faster-moving object requires a greater force when the mass and radius are constant c. The radius of the circle: a smaller radius requires a greater force to keep the speed and radius constant 22. Friction (energy is transferred by heating when it occurs) can be reduced by: a. Smoothing the surface b. Lubricating the surface c. Liquid/ gases: streamlining object 23. Friction in gases and liquids: drag 24. Equilibrium: state of balance/ stability a. No resultant force b. No resultant moment 25. For a symmetrical object of uniform density, the centre of gravity is located at the point of symmetry 26. If the line of action of the weight force lies outside the base of the object, there will be a resultant moment, and the body will topple 27. A closed system means that no energy is transferred into or out of the system and there are no external forces acting 28. 29. 30. Energy is transferred as work is done 31. Efficiency: the ratio of the useful power or energy output from a system to its total power or energy input 32. 1 Pa = 1 N/m2 33. In a column of water, the highest pressure would be at the bottom Unit 2: 1. When a substance changes state, the only thing that changes is the energy of the molecules 2. Brownian motion is the random movement of particles in a liquid or a gas produced by large numbers of collisions with smaller particles which are often too small to see 3. Molecules in a gas are in constant random zigzag motion at high speeds 4. Volume and pressure graph is a downward curve 5. Thermal expansion happens because: a. The molecules start to move around (or vibrate) faster as they gain kinetic energy b. This causes them to collide with each other more often and push each other apart 6. Consequences of thermal expansion: a. Buckling of metal railroad tracks, bridges and road surfaces 7. Objects that are prone to buckling in this way have gaps built in to creates space for the expansion to happen without causing damage 8. Uses of thermal expansion: a. Liquid in glass thermometer that relies on the expansion of mercury in higher temperatures b. Temperature-activated switches utilise a bimetallic (made from two types of metal) strip which consists of two metals that expand at different rates and bends by a predictable amount at a given temperature 9. Rise in temperature of object= higher internal energy 10. Internal energy: the total energy stored inside a system by the particles that make up the system due to their motion and positions 11. At melting/ boiling points, more energy is added but temperature doesn’t change because energy is used to overcome intermolecular forces of attraction 12. Evaporation happens at any temperature and only from the surface of a liquid 13. 14. Thermal equilibrium: a point where an object is absorbing radiation at the same rate as it is emitting radiation 15. Thermal energy transfers always move towards thermal equilibrium 16. A wood (or coal) fire in a room heats it through radiation and convection: a. As the fuel is so hot in a wood fire, it transfers a lot of thermal energy to the room through radiation b. The fire transfers a much greater amount of thermal energy to nearby objects via radiation c. Air surrounding the fire is heated and rises, forming a convection current d. This transfers thermal energy throughout the whole room 17. A car radiator transfers heat away from the engine, which reaches high temperatures: a. A liquid travels between the radiator and the engine b. When the liquid passes over the engine, it absorbs energy from the engine through conduction c. This liquid then travels back to the radiator and transfers heat to the radiator, again by conduction d. The radiator then transfers thermal energy to the surrounding air through radiation e. A car radiator is a dark colour, which allows it to emit more radiation f. A large surface area also helps g. Once the radiator has absorbed thermal energy from the liquid, the liquid is cooler and the cycle begins again Unit 3: 1. Wave Properties: They transfer energy, without transferring matter. It is the wave that travels, not the air molecules. 2. Waves: oscillations about a fixed point 3. Wavefronts are a useful way of picturing waves from above: each wavefront is used to represent a single wave a. When the wavefronts are close together, this represents a wave with a short wavelength b. When the wavefronts are far apart, this represents a wave with a long wavelength 4. Wavelength: the distance from one point on a wave to the same point on the next wave. a. In a transverse wave: The wavelength can be measured from one peak to the next peak b. In a longitudinal wave: The wavelength can be measured from the center of one compression to the center of the next 5. Frequency: number of waves passing a point in a second 6. Wave speed: the distance traveled by a wave each second 7. Reflection: occurs when a wave hits a boundary between two media at a plane surface and does not pass through, but instead stays in the original medium 8. Refraction: occurs when a wave passes a boundary between two different transparent media and undergoes a change in speed a. If the waves slow down, they will bunch together, causing the wavelength to decrease (rarer to denser for light) i. The waves will also start to turn slightly towards the normal b. If the waves speed up then they will spread out, causing the wavelength to increase (denser to rarer for light) i. The waves will also turn slightly away from the normal c. When a wave refracts, as well as a change in speed, the wave also undergoes: i. A change in wavelength (but frequency stays the same) ii. A change in direction 9. Diffraction: occurs when waves pass through a narrow gap and the waves spread out a. The extent of diffraction depends on the width of the gap compared with the wavelength of the waves b. Diffraction is the most prominent when the width of the slit is approximately equal to the wavelength c. As the gap gets bigger, the effect gradually gets less pronounced until, in the case that the gap is very much larger than the wavelength, the waves no longer spread out at all d. Around a barrier, the greater the wavelength, the greater the diffraction 10. Optically denser objects have a higher refractive index 11. Refractive index: The ratio of the speeds of a wave in two different regions 12. TIR occurs when light passes from a denser to a rarer medium and all the right is reflected 13. Principal axis: line which passes through the center of a lens 14. Focal length is the distance between the center of the lens and the principal focus 15. Focus point is the point at which rays of light travelling parallel to the principal axis intersect the principal axis and converge, or the point at which diverging rays appear to proceed 16. Converging: convex lens: focuses light 17. More curved lens= shorter focal length 18. Real images produced by convergence of light 19. Pl ImN O Si Be Be R In D A A R In Sa Be Be R In M Be A Vi U M 20. All images formed by diverging lenses are diminished 21. Converging lenses can be used to correct long-sighted vision (hypermetropia) 22. Diverging lenses can be used to correct short-sighted vision (myopia) 23. When sound waves come in contact with a solid, longitudinal waves are transferred to the solid 24. Longitudinal: parallel, draw lines 25. Ultrasound waves that reach a crack in an object, such as a metal bar, are reflected back from the crack earlier than the waves that continue to be absorbed through the object a. The reflected waves are displayed as pulses on an oscilloscope trace b. This allows engineers to assess the structure of an object 26. In medicine: The ultrasound waves are reflected back to the transducer by boundaries between tissues in the path of the beam to form images. 27. 3.4: Refer to syllabus Unit 4: 1. Magnetic materials: cobalt, nickel, iron and steel 2. Permanent magnet produces its own magnetic field; doesn’t lose magnetism 3. Induced magnet becomes a magnet temporarily when placed in a magnetic field 4. Magnetic field is a region in which a magnetic pole experiences a force 5. Plotting magnetic fields (2 ways): a. Iron fillings b. Plotting compasses 6. 7. Electrical hazards: a. damaged insulation: can touch metal part= electrocution b. overheating cables: excess current c. damp conditions: water is conductor. damp in live wire= short circuit = fire d. excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply: heat= fires 8. Wires: a. Live wire: carry AC current from mains supply to circuit b. Neutral wire: form opposite end of circuit to live wire to complete circuit c. Earth wire: act as a safety wire to prevent appliance from becoming live i. If a live wire came in contact with a metal case, case would become electrified ii. The earth wire provides a low resistance path to the earth iii. It causes a surge of current in the earth wire and hence also in the live wire iv. The high current through the fuse causes it to melt and break v. This cuts off the supply of electricity to the appliance, making it safe 9. An electromotive force (e.m.f.) is induced in a conductor whenever there is relative movement between the conductor and a magnetic field 10. Direction of induced current always opposes the change producing it a. Changing magnetic field induces emf b. Induced emf causes current to flow and generates magnetic field in coil c. Magnetic field due to current opposes the magnet being pulled away from coil d. End becomes same pole as one pulled out last e. Attracts opposite pole 11. AC generator a. Motion to electrical output b. c. Max emf= horizontal + motion perpendicular d. Min emf= vertical + motion parallel e. The magnitude of the induced e.m.f. can be increased by: i. increasing the frequency of rotation of the coil ii. increasing the number of turns on the coil iii. increasing the strength of the magnet iv. inserting a soft iron core into the coil 12. Relay: a. A magnetic field is induced around the coil. The magnetic field attracts the switch and causes it to pivot and close contacts in the second circuit, allowing current to flow in the second circuit as well. 13. Electric bell: a. When a button is pressed, current flows through the circuit and electromagnet, attracting the iron armature. As the iron armature moves, it causes it to strike the bell. The movement of the armature causes the circuit to break, stopping current flow and destroying magnetic field, making the armature return to its position. 14. In a solenoid, the north pole forms at the end where the current flows anti-clockwise, and the south pole at the end where the current flows clockwise 15. A particle travelling perpendicular to the field lines will experience maximum force 16. The Motor Effect (DC motors): a. A current flows through the coil, which produces a magnetic field around the coil. This magnetic field interacts with the field between the poles of the (permanent) magnet. This produces a force, the direction of which is given by Fleming’s left hand rule. Therefore the coil moves. The current through the coil is alternating. As the current changes direction, so does the force on each side of the coil. b. In a loudspeaker: This makes the coil vibrate. This makes the diaphragm (attached to the coil) vibrate. This makes a series of compressions and rarefactions in the air, producing a soundwave. 17. Transformers: there is an alternating current in the primary coil, which produces a magnetic field (flux), and passes through the core to cut the secondary coil. Changing flux induces emf in the secondary coil, thus inducing AC current in the secondary coil. Unit 5: 1. Gold foil experiment: a. Most of the alpha particles passed straight through the foil because the atom is mostly empty space b. Some of the alpha particles changed direction but continued through the foil because the positive nucleus repels the positive α-particles c. A few of the alpha particles bounced back off the gold foil because the nucleus is tiny 2. An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons 3. Mass number= nucleon number: A 4. Proton number: Z 5. Relative charge is the ratio of the charge of a particle compared to the fundamental charge a. Fundamental charge: 1.6 × 10−19 C 6. Nuclear charge: relative charge of nucleus 7. Fission and fusion: a. Fission: the splitting of a large, unstable nucleus into two smaller nuclei b. The products of fission move away very quickly (energy transferred from nuclear store of parent to kinetic energy of reactants) c. Fusion: when two light nuclei join to form a heavier nucleus d. Stars use nuclear fusion to produce energy and requires extremely high temperature and pressure, making it hard to reproduce on Earth e. Mass is less than original as remaining mass has been converted to energy which is released during the processes 8. Background radiation is that which exists around us all the time a. Radon gas from uranium decay b. Rocks and buildings c. Food and drinks d. Cosmic rays (sun) e. Carbon 14 in biological material f. Medical sources g. Nuclear waste/ fallout/ accidents 9. Count rate= number of decays per second 10. Radiation detectors a. Geiger counter b. Photographic film c. Ionisation chambers d. Spark counters e. Scintillation counters 11. Amount of radiation received by a person is called the dose. 12. Emission of radiation: spontaneous and random a. Random: cannot be predicted b. Spontaneous: is not affected by external factors Unit 6: 1. The Solar System Planets: Our solar system consists of 8 planets orbiting the Sun. These planets follow elliptical orbits. a. Moons: Natural satellites that orbit planets (e.g., Earth’s Moon). b. Asteroids and Comets: i. Asteroids: Small rocky bodies orbiting the Sun, mostly found in the asteroid belt between Mars and Jupiter. ii. Comets: Icy bodies with highly elliptical orbits, developing tails when close to the Sun due to sublimation of ice. 2. Gravity in the Solar System a. Gravitational Attraction: The force keeping planets in orbit around the Sun and moons around planets. The force is stronger for larger masses and closer objects. b. Orbital Speed: Planets closer to the Sun have higher orbital speeds due to stronger gravitational pull. 3. Life Cycle of Stars Nebula: Stars form from clouds of gas and dust, which collapse under gravity. a. Main Sequence Star: A stable star where nuclear fusion of hydrogen into helium occurs in the core, releasing energy. b. Red Giant/Supergiant: As hydrogen runs out, the core contracts and the outer layers expand, becoming cooler (red giant or supergiant, depending on mass). c. White Dwarf: Low to medium-mass stars shed their outer layers and the core remains as a white dwarf. d. Supernova: Massive stars explode in a supernova, spreading elements across space. e. Neutron Star or Black Hole: After a supernova, the core may become a neutron star (if it’s relatively small) or collapse into a black hole (if it’s massive). 4. Orbits a. Geostationary Orbits: Satellites orbit the Earth at the same rate as the Earth's rotation, staying above the same point (used for communication). b. Polar Orbits: Satellites that pass over the Earth's poles, covering the entire surface (used for mapping and weather monitoring). 5. The Expanding Universe a. Redshift: Light from distant galaxies is shifted toward the red end of the spectrum, indicating that galaxies are moving away from us. b. Big Bang Theory: The universe began from a singular point and has been expanding ever since. Evidence includes cosmic microwave background radiation and redshift. 6. Light Years: The distance light travels in one year, used to measure distances in space. 7. Values: a. Light year: 9.5 x 10^15 b. Hubble’s constant: 2.2 x 10^−18 s c. Orbital speed: 2 x pi x r/ T d. Hubble’s constant: v/d Note: for unit 5 & 6, refet to Vasumitra Gajbhiye notes as well

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