Fundamental Physics for Radiographers PDF

RXD12402 FUNDAMENTAL PHYSICS FOR RADIOGRAPHERS Izza Nadia binti Mohd Maulana Senior Lecturer  1. Introduction to physics. 2. Work, Energy and Power. 3. Properties of Electrical Charges. SUBTOPICS 4. Law of Conservatio...

RXD12402 FUNDAMENTAL PHYSICS FOR RADIOGRAPHERS Izza Nadia binti Mohd Maulana Senior Lecturer  1. Introduction to physics. 2. Work, Energy and Power. 3. Properties of Electrical Charges. SUBTOPICS 4. Law of Conservation of Energy. 5. Heat and Temperature. 6. Heat Transfer. 7. Heat Energy in X-ray Tube. 2  At the end of this topic, students should be able to: 1. Describe work, energy (potential and kinetic energy), and power. 2. Describe the law of conservation TOPIC of energy. LEARNING 3. Describe the electrical charges OUTCOMES and Coulomb’s Law. 4. Describe heat and temperature. 5. Describe the process of transfer: conduction, convection and radiation. 3 Introduction to Physics The Introduction Physics is concerned with describing the interactions of energy, matter, space, and time, and it is especially interested in what fundamental mechanisms underlie every phenomenon. Physics aims to describe the function of everything around us, from the movement of tiny charged particles to the motion of people, cars, and spaceships. In fact, almost everything around you can be described quite accurately by the laws of physics. 5 Structural Lighting stability Acoustics Electricity Cooling Heating 6  Radioactive Heat transfer dating of rocks Earthquake analysis Air quality 7 Physical Quantities & Units We define a physical quantity either by specifying how it is measured or by stating how it is calculated from other measurements. For example, we define distance and time by specifying methods for measuring them, whereas we define average speed by stating that it is calculated as distance traveled divided by time of travel. Measurements of physical quantities are expressed in terms of units, which are standardized values. Without standardized units, it would be extremely difficult for scientists to express and compare measured values in a meaningful way. 8 Base Quantity A base quantity is a physical quantity which cannot be derived in terms of other l physical quantities. m The measuring unit is known t as a base unit. T They are only 5 base I quantities. 9 Derived Quantities A derived quantity is a physical quantity produced from the combination of base quantities through multiplication, division, or both. 10 Metric Prefixes Metric systems have the advantage that conversions of units involve only powers of 10. In nonmetric systems, such as the system of U.S. customary units, the relationships are not as simple—there are 12 inches in a foot, 5280 feet in a mile, and so on. Another advantage of the metric system is that the same unit can be used over extremely large ranges of values simply by using an appropriate metric prefix. 9/3/20XX Presentation Title 11 12 Displacement vs. Distance DISPLACEMENT DISTANCE This change in position is known Distance is the magnitude or size as displacement. of displacement between two The word “displacement” implies positions. that an object has moved, or has Distance traveled is the total been displaced. length of the path traveled Displacement has a direction as between two positions. well as a magnitude. 9/3/20XX Presentation Title 13  5m A (xo)=0m B 2.5 m C (xf) B DISTANCE POSITION DISPLACEMENT TRAVELLED A ∆x= xf – xo ABC= B A  B  C= 5m + 2.5m = C 2.5m – 0m = - 7.5m 2.5m 14 Work, Energy & Power  Work The work done on a system by a constant force is the product of the component of the force in the direction of motion times the distance through which the force acts. W = |Force (N)|cosθ|distance (m)| W = F d cosθ Unit for W = Nm = Joule (J) Notes: 1 N = 1 kgms-2 16 Example - work 30o 15 kg A 100 N force is applied at an angle of 30o to the horizontal to move a 15 kg object at a constant speed for a horizontal distance of 5 m. W = F.d cos θ = 100N X 5m cos 30o = 433Nm @ 433J 17  To find the work done on a system that undergoes motion that is not one- way or that is in two or three dimensions, we divide the motion into one- way one-dimensional segments and add up the work done over each segment. 18 Energy in Kinematics Kinematics is the study of the motion of mechanical points, bodies and system. There are two types of energy Potential energy. Kinetic energy. 19 Potential Energy An object can store energy as a result of its position. This stored energy of position is referred to as potential energy. The formula of PE is: PE = mass (kg) x gravity (ms-2) x height (m) = mgh g = 9.81 m/s2 or 10 m/s-2 Unit of PE = kgm2s-2 = Joules (J) 20  Example 1: PE = mgh m = 0.86 kg = 0.86 kg x 9.8 m/s2 A rock of mass x 10.3 m 0.86kg is released from rest from a = 86.81 kgm2s-2 10.3 m tall building. = 86.81 J 10.3 m What is its potential energy? (g = 9.8 m/s2) 21 m = 9.56 kg Example 2: PE = mgh = 9.56 kg x 9.8 m/s2 What is the x 4.25 m potential energy = 398.17 kgm2s-2 of a 9.56 kg mass = 398.17 J 4.25 m raised to a height of 4.25 m? (g = 9.8 m/s2) 22 Kinetic Energy Kinetic energy is the energy an object has because of its motion. Kinetic energy depends on the mass and the velocity of an object. The formula for KE is: KE = ½ x mass (kg) x velocity (ms-1) square = ½ mv2 Unit of KE = kgm2s-2 = Joules (J) 23 Presentation Title 24 Example 1: KE = ½ mv2 KE = ½ x 2500 kg An elephant of x (6.2 m/s)2 mass 2500 kg travelling at 6.2 = 48,050 kgm2s-2 m/s has kinetic = 48,050 Joules energy? 25 Example 2: KE = ½ mv2 = ½ x 3.8 kg x (20 m/s)2 What is the = 760 kgm2s-2 kinetic energy of = 760 J a 3.8 kg shot-put thrown by an athlete at a speed of 20 m/s? 26 Conservation of Energy 27 28 The Work Energy Theorem KEi + PEi + Wnc = KEf + PEf KEi = Kinetic energy initial Wnc = F. d cosθ PEi = Potential energy initial = Ffriction. d cosθ Wnc = Work non-conservative force = µ (mg). d cosθ KEf = Kinetic Energy final Ffriction = µ. Fnormal PEf = Potential energy final = µ (mg) µ = coefficient of friction 29 Example: A man is traveling down a level roadway with a speed of 8.00 m/s. He slams on the brakes and encounters a coefficient of friction of 0.816. What distance does his 925 kg car skid before stopping? KEi + PEi + Wnc = KEf + PEf (1/2 mv2) + 0 + (Ffric. d cos 180o) = 0 + 0 (1/2 mv2) + (µmg x d x -1) = 0 (1/2 x 925 kg x (8 m/s)2) + (0.816 x 925 kg x 9.8 ms-2 x d x -1) = 0 29,600kgm2s-2 + (-7,397.04 kgms-2 x d) = 0 29,600kgm2s-2 – (7,397.04 kgms-2 x d) = 0 7,397.04 kgms-2 x d = 29,600kgm2s-2 d = 29,600kgm2s-2 7,397.04 kgms-2 d = 4.00 m 30  Power Power (P) is the rate at which work is done. It also describes how much work is done per unit time. Power = energy transferred (J) time taken (s) = work done (J) time taken (s) The unit of power is the Watt (SI unit), equivalent to J/s. 1 Watt = 1J/s (1 horse power = 746 watts) 31 Electrical Charges Introduction Electric charge can be defined as a fundamental property of subatomic particles that gives rise to the phenomenon of experiencing force in the presence of electric and magnetic fields. Electric charge comes in two main types: positive and negative charges. Positive charges are associated with protons, and are denoted by the symbol of “+”. Negative charges are linked to electrons, and are denoted by the symbol of “-“. Unit = Coulomb (C) 33 34 The Properties of Electrical Charges Additivity of Electric Charge When charges combine, their magnitudes add up algebraically. For example, if we have a positive charge of +3 units and a negative charge of -2 units, the resulting charge would be +1 unit. Conservation of Electric Charge: In an isolated system, electric charge is conserved. This means that the total electric charge within the system remains constant over time. Quantization of Electric Charge Electric charge comes in discrete, indivisible units called elementary charges. This quantization of charge implies that electric charge cannot be divided into smaller parts. Charge of: QUANTIZED Electron = - 1.6 x 10-19 C INDIVISIBLE Proton = +1.6 x 10-19 C 35 Coulomb’s Law Charges repel each other. Therefore, Coulomb’s Law explained k q1 q 2 the strength of these forces acting F between charges. r2 Definition: The magnitude of the electrostatic qq=value value of charge of charge force between two point charges is r = separation of charges directly proportional to the product of their magnitudes and inversely k = proportionality constant proportional to the square of the distance separating them. 36  Heat and Temperature Presentation Title 39 Specific Heat Capacity  The specific heat capacity of a substance is the quantity of heat needed to increase the temperature of mass of 1 kg by 1 oC or 1 K.  Specific heat capacity can be calculated from the amount of heat supplied, Q to a mass, m of the substance and the increase in temperature, ΔT. (unit : J kg-1 K-1 ) m ΔT  The quantity of heat absorbed or lost from a body is given by Q = m c ΔT |ΔT| =Always positive 40  Specific Heat Substance Capacity Difference (J kg-1 K-1) substance are said Water 4200 to have different specific heat Ice 2100 capacities, c. Ethanol 2400 Copper 390 Aluminium 900 Glass 840 Mercury 140 Wood 1700 Lead 130 41 Heat Transfer What is Heat Transfer? Heat transfer is the exchange of thermal energy between physical objects. Heat will naturally flow from a hotter to a colder object (2nd Law of Thermodynamics). Thermal equilibrium happens when all involved objects and their environment reach the same temperature.  There are essentially three ways that heat can be transferred: 1. Conduction 2. Convection 3. Radiation 44 Conduction Conduction is the transfer of heat within a substance, molecule by molecule. If you put one end of a metal rod over a fire, that end will absorb the energy from the flame (this is radiation transferring energy). The molecules at this end of the rod will gain energy and begin to vibrate faster. As they do their temperature increases and they begin to bump into the molecules next to them. The heat is being transferred from the warm end to the cold end. 45 Ironing of clothes is an Heat is transferred from Heat conduction through example of conduction hands to ice cube the sand at the beaches. where the heat is resulting in the melting This can be experienced conducted from the of an ice cube when during summers. Sand is a iron to the clothes. held in hands. good conductor of heat. 46 Convection Convection is heat transfer by the mass movement of a fluid in the vertical (up/down) direction, the movement of the hot particles to cooler areas. This type of heat transfer takes place in liquids and gases. Air or water surrounding a heat source receives heat, becomes less dense, and rises. The surrounding, cooler fluid moves to replace it. This cooler fluid is then heated and the process continues, forming a convection current. 47 Boiling of water, that is molecules that Blood circulation in warm-blooded are denser move at the bottom while animals takes place with the help of the molecules which are less dense convection, thereby regulating the move upwards resulting in the circular body temperature. motion of the molecules so that water gets heated. 48 Radiation Radiation allows heat to be transferred through wave energy. These waves are called Electromagnetic Waves (EM), because the energy travels in a combination of electric and magnetic waves. This energy is released when these waves are absorbed by an object. For example, energy traveling from the sun to your skin, you can feel your skin getting warmer as energy is absorbed. 49  Microwave radiation UV rays coming from The release of alpha emitted in the oven is the sun. particles during the an example of radiation. decaying of Uranium- 238 into Thorium-234. 50 Heat Energy in X- Ray Tube  As with any vacuum tube, there is a cathode, which emits electrons into the vacuum and an anode to collect the electrons, thus establishing a flow of electrical current, known as the beam, through the tube. More than 99% of the kinetic energy of projectile electrons is converted to thermal energy, leaving less than 1% available for the production of x-radiation. 53 Tube Cooling The x-ray tube uses all three forms of cooling.  Radiation  Conduction  Convection 9/3/20XX Presentation Title 54 RADIATION 55 RADIATION CONVECTION CONDUCTION 56 Heat Unit  During x-ray production, most of the kinetic energy of the electrons is converted to heat.  This heat can damage the x-ray tube and anode target.  The amount of heat produced with any given exposure is expressed by a unit called the heat unit (HU). HU= kVp x mA x time(s)  The number of HUs produced depends on the type of X-ray generator being used and on the exposure factors selected for a particular procedure. (CT scan) 9/3/20XX Presentation Title 57 Thank you 58