Energ and Energy Forms, Work, and Power | IGCSE Physics
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This extensive slide deck provides a detailed exploration of energy, work, and power for IGCSE Physics. It covers fundamental concepts such as the definition of work done, kinetic energy, potential energy, mechanical energy, conservation of energy, efficiency, and power. The presentation also includes energy transfer, renewable and non-renewable energy sources, calculation of work done, power output, and real-life applications of energy principles. Featuring illustrative diagrams, worked examples, and exam-style questions, this resource is ideal for IGCSE students, teachers, and independent learners preparing for exams.
Energ and Energy Forms, Work, and Power | IGCSE Physics
- 2. Energy • Energy is a property of an object that is stored or transferred • Energy must be transferred to an object to perform work on or heat up that object • Energy is measured in units of joules (J) Systems 1/3 • Energy will often be described as part of an energy system • In physics, a system is defined as: • An object or group of objects BLESSING NDAZIE 2 ENERGY, WORK & POWER
- 3. Systems 2/3 • In physics, defining the system is a way of narrowing the parameters to focus only on what is relevant to the situation being observed • A system could be as large as the whole Universe, or as small as an apple sitting on a table • When a system is in equilibrium, nothing changes, and so nothing happens • When there is a change to a system, energy is transferred • If an apple sits on a table and that table is suddenly removed, the apple will fall • As the apple falls, energy is transferred BLESSING NDAZIE 3 ENERGY, WORK & POWER
- 4. Systems 3/3 • A closed system is defined as: • A system where there is no net change to the total energy in that system • As a result, the total amount of energy within that system must remain constant • This is due to the conservation of energy BLESSING NDAZIE 4 ENERGY, WORK & POWER
- 5. BLESSING NDAZIE 5 Example of a system In physics, a system is an object or group of objects being observed or studied. Energy is transferred when a change happens within a system ENERGY, WORK & POWER
- 6. Energy stores • Energy is stored in objects in different energy stores BLESSING NDAZIE 6 ENERGY, WORK & POWER
- 7. Kinetic Energy Store • Moving objects have energy in their kinetic store BLESSING NDAZIE 7 ENERGY, WORK & POWER
- 8. • Objects gain energy in their gravitational potential store when they are lifted through a gravitational field BLESSING NDAZIE 8 Gravitational Potential Energy Store ENERGY, WORK & POWER
- 9. • Objects have energy in their elastic potential store if they are stretched, squashed or bent BLESSING NDAZIE 9 Elastic Potential Energy Store ENERGY, WORK & POWER
- 10. • Magnetic materials interacting with each other have energy in their magnetic store BLESSING NDAZIE 10 Magnetic Energy Store ENERGY, WORK & POWER
- 11. • Objects with charge (like electrons and protons) interacting with one another have energy in their electrostatic store BLESSING NDAZIE 11 Electrostatic Energy Store ENERGY, WORK & POWER
- 12. • Chemical reactions transfer energy into or away from a substance's chemical store BLESSING NDAZIE 12 Chemical Energy Store ENERGY, WORK & POWER
- 13. • Atomic nuclei release energy from their nuclear store during nuclear reactions BLESSING NDAZIE 13 Nuclear Energy Store ENERGY, WORK & POWER
- 14. • All objects have energy in their thermal stores; the hotter the object, the more energy it has in this store BLESSING NDAZIE 14 Thermal Energy Store ENERGY, WORK & POWER
- 15. BLESSING NDAZIE 15 ENERGY, WORK & POWER
- 16. BLESSING NDAZIE 16 ENERGY, WORK & POWER
- 17. BLESSING NDAZIE 17 ENERGY, WORK & POWER
- 18. BLESSING NDAZIE 18 ENERGY, WORK & POWER
- 19. BLESSING NDAZIE 19 Summary of Energy Store • Energy is transferred between energy stores. • Energy transfer can occur; o Between different stores in the same object o Between the same stores in different objects o Between different stores in different objects • Make sure to always make it clear which store energy is being transferred from and transferred to. ENERGY, WORK & POWER
- 20. BLESSING NDAZIE 20 Summary of Energy Store • Energy is transferred between energy stores. • Energy transfer can occur; o Between different stores in the same object o Between the same stores in different objects o Between different stores in different objects • Make sure to always make it clear which store energy is being transferred from and transferred to. ENERGY, WORK & POWER
- 21. Energy transfers • Energy is transferred between stores through different energy transfer pathways • Energy transfer pathways • The energy transfer pathways are: • Mechanical • Electrical • Heating • Radiation BLESSING NDAZIE 21 ENERGY, WORK & POWER
- 22. Table of energy transfer pathways Transfer Pathway Description Mechanical working When a force acts on an object (e.g. pulling, pushing, stretching, squashing) Electrical working A charge moving through a potential difference (e.g. current) Heating (by particles) Energy is transferred from a hotter object to a colder one (e.g. conduction) (Heating by) radiation Energy transferred by electromagnetic waves (e.g. visible light) BLESSING NDAZIE 22 ENERGY, WORK & POWER
- 23. BLESSING NDAZIE 23 Transfer Pathway; Mechanical ENERGY, WORK & POWER
- 24. BLESSING NDAZIE 24 Transfer Pathway; Electrical ENERGY, WORK & POWER
- 25. BLESSING NDAZIE 25 Transfer Pathway; Heating (by particles) ENERGY, WORK & POWER
- 26. BLESSING NDAZIE 26 Transfer Pathway; Radiation ENERGY, WORK & POWER
- 27. BLESSING NDAZIE 27 What is the pathway here ENERGY, WORK & POWER
- 28. Worked Example • Describe the energy transfers in the following scenarios: • a) A battery powering a torch • b) A falling object BLESSING NDAZIE 28 ENERGY, WORK & POWER
- 29. Answer: Part a) Step 1: Determine the store that energy is being transferred away from, within the parameters described by the defined system For a battery powering a torch The system is defined as the battery and the torch Therefore, the energy began in the chemical store of the cells of the battery Step 2: Determine the store that energy is transferred to, within the parameters described by the defined system When the circuit is closed, the bulb lights up Therefore, energy is transferred to the thermal store of the bulb Energy is then transferred from the bulb to the surroundings, but this is not described in the parameters of the system BLESSING NDAZIE 29 ENERGY, WORK & POWER
- 30. Answer: Step 3: Determine the transfer pathway Energy is transferred by the flow of charge around the circuit Therefore, the transfer pathway is electrical Step 4: State the energy transfer Energy is transferred electrically from the chemical store of the battery to the thermal store of the bulb BLESSING NDAZIE 30 ENERGY, WORK & POWER
- 31. Answer: • Part b) • Step 1: Determine the store that energy is being transferred away from, within the parameters described by the defined system • For a falling object • In order to fall, the object must have been raised to a height • Therefore, it began with energy in its gravitational potential store • Step 2: Determine the store that energy is transferred to, within the parameters described by the defined system • As the object falls, it is moving • Therefore, energy is being transferred to its kinetic store BLESSING NDAZIE 31 ENERGY, WORK & POWER
- 32. Answer: • Step 3: Determine the transfer pathway • For an object to fall, a resultant force must be acting on it, and that force is weight, and it acts over a distance (the height of the fall) • Therefore, the transfer pathway is mechanical • Step 4: State the energy transfer • Energy is transferred from the gravitational store to the kinetic store of the object via a mechanical transfer pathway BLESSING NDAZIE 32 ENERGY, WORK & POWER
- 33. BLESSING NDAZIE 33 ENERGY, WORK & POWER
- 34. BLESSING NDAZIE 34 ENERGY, WORK & POWER
- 35. Kinetic energy • Energy in an object's kinetic store is defined as: • The amount of energy an object has as a result of its mass and speed • This means that any object in motion has energy in its kinetic energy store • If an object speeds up, energy is transferred to its kinetic store • If an object slows down, energy is transferred away from its kinetic store BLESSING NDAZIE 35 ENERGY, WORK & POWER
- 36. Kinetic energy equation • The amount of energy in an object's kinetic store can be calculated using the equation: BLESSING NDAZIE 36 •Where: • = kinetic energy, measured in joules (J) • = mass of the object, measured in kilograms (kg) • = speed of the object, measured in metres per second (m/s) ENERGY, WORK & POWER
- 37. Kinetic energy equation BLESSING NDAZIE 37 •The kinetic energy equation demonstrates that if the mass of an object is doubled for a given speed, then its kinetic energy will double •This is because kinetic energy is directly proportional to mas • •If the speed of the object is doubled for a given mass, it will have four times the kinetic energy •This is because kinetic energy is directly proportional to velocity squared • ENERGY, WORK & POWER
- 38. Worked Example • Calculate the kinetic energy stored in a vehicle of mass 1200 kg moving at a speed of 27 m/s. BLESSING NDAZIE 38 ENERGY, WORK & POWER
- 39. Worked Example BLESSING NDAZIE 39 ENERGY, WORK & POWER
- 40. Examiner Tips and Tricks • When performing calculations using the kinetic energy equation, always double-check that you have squared the speed. Forgetting to do this is the most common mistake that students make. • You will most likely need to rearrange the kinetic energy equation in your IGCSE exam. The kinetic energy equation is one of the more difficult rearrangements at IGCSE, so make sure you are comfortable doing it before your exam! BLESSING NDAZIE 40 ENERGY, WORK & POWER
- 41. Gravitational potential energy • Energy in an object's gravitational potential energy store is defined as: • The energy an object has due to its height in a gravitational field • Work is done against the weight force exerted on the object; therefore, energy is transferred • This means that: • if an object is lifted up, energy will be transferred to its gravitational potential store • if an object is lowered, energy will be transferred away from its gravitational potential store BLESSING NDAZIE 41 Energy is transferred to the mass's gravitational store as it is lifted through the gravitational field ENERGY, WORK & POWER
- 42. • The change in energy in an object's gravitational potential energy store can be calculated using the equation: Gravitational potential energy equation BLESSING NDAZIE 42 ENERGY, WORK & POWER
- 43. Worked Example • A man climbs a flight of stairs that is, in total, 3.0 m higher than the floor. The man has a mass of 72 kg, and the gravitational field strength on Earth is approximately 9.8 N/kg. • Calculate the energy transferred to the man's gravitational potential energy store. BLESSING NDAZIE 43 ENERGY, WORK & POWER
- 44. Worked Example BLESSING NDAZIE 44 ENERGY, WORK & POWER
- 45. Conservation of energy • The principle of conservation of energy states that: • Energy cannot be created or destroyed, it can only be transferred from one store to another • The principle of conservation of energy means that for a closed system, the total amount of energy is constant • The total amount of energy transferred into the system must be equal to the total amount of energy transferred away from the system • Therefore, energy cannot be ‘lost’, but it can be transferred to the surroundings • Energy can be dissipated (spread out) to the surroundings by heating and radiation • Dissipated energy transfers are often not useful, in which case they can be described as wasted energy BLESSING NDAZIE 45 ENERGY, WORK & POWER
- 46. Examples of the principle of conservation of energy • Example 1: a bat hitting a ball • The moving bat has energy in its kinetic store • Some of that energy is transferred usefully to the kinetic store of the ball • Some of that energy is transferred from the kinetic store of the bat to the thermal store of the ball mechanically due to the impact of the bat on the ball • This energy transfer is not useful; the energy is wasted • Some of that energy is dissipated by heating to the thermal store of the bat, the ball, and the surroundings • This energy transfer is not useful; the energy is wasted • The total amount of energy transferred into the system is equal to the total amount of energy transferred away from the system BLESSING NDAZIE 46 ENERGY, WORK & POWER
- 47. BLESSING NDAZIE 47 Conservation of energy: a bat hitting a ball ENERGY, WORK & POWER
- 48. Conservation of energy: a bat hitting a ball BLESSING NDAZIE 48 The principle of conservation of energy applied to a bat hitting a ball ENERGY, WORK & POWER
- 49. Example 2: Boiling Water in a Kettle • When an electric kettle boils water, energy is transferred electrically from the mains supply to the thermal store of the heating element inside the kettle • As the heating element gets hotter, energy is transferred by heating to the thermal store of the water • Some of the energy is transferred to the thermal store of the plastic kettle • This energy transfer is not useful; the energy is wasted • And some energy is dissipated to the thermal store of the surroundings due to the air around the kettle being heated • This energy transfer is not useful; the energy is wasted • The total amount of energy transferred into the system is equal to the total amount of energy transferred away from the system BLESSING NDAZIE 49 ENERGY, WORK & POWER
- 50. Conservation of energy: a kettle boiling water BLESSING NDAZIE 50 ENERGY, WORK & POWER
- 51. Energy flow diagrams • Energy stores and transfers can be represented using a flow diagram • This shows both the stores and the transfers taking place within a system BLESSING NDAZIE 51 ENERGY, WORK & POWER
- 52. BLESSING NDAZIE 52 ENERGY, WORK & POWER
- 53. Worked Example BLESSING NDAZIE 53 ENERGY, WORK & POWER
- 54. • At point A: • The rollercoaster is raised above the ground, therefore it has energy in its gravitational potential store • As it travels down the track, energy is transferred mechanically to its kinetic store • At point B: • Energy is transferred mechanically from the kinetic store to the gravitational potential store • As the kinetic energy store empties, the gravitational potential energy store fills • At point C: • Energy is transferred mechanically from the gravitational potential store to the kinetic store • At point D: • The flat terrain means there is no change in the amount of energy in its gravitational potential store, the rollercoaster only has energy in its kinetic store • The kinetic energy store is full • In reality, some energy will also be transferred to the thermal energy store of the tracks due to friction, and to the thermal energy store of the surroundings due to sound • We say this energy is dissipated to the surroundings • The total amount of energy in the system will be constant • Total energy in = total energy out BLESSING NDAZIE 54 ENERGY, WORK & POWER
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- 56. Sankey diagrams • Sankey diagrams can be used to represent energy transfers • Sankey diagrams are characterised by arrows that split to show the proportions of the energy transfers taking place • The different parts of the arrow in a Sankey diagram represent the different energy transfers: • The left-hand side of the arrow (the flat end) represents the energy transferred into the system • The straight arrow pointing to the right represents the energy that ends up in the desired store; this is the useful energy output • The arrows that bend away represent the wasted energy BLESSING NDAZIE 56 ENERGY, WORK & POWER
- 57. Features of a Sankey diagram BLESSING NDAZIE 57 ENERGY, WORK & POWER
- 58. Features of a Sankey diagram • The width of each arrow is proportional to the amount of energy being transferred • As a result of the conversation of energy: • total energy in = total energy out • total energy in = useful energy out + wasted energy • A Sankey diagram for a modern efficient light bulb will look very different from that for an old filament light bulb • A more efficient light bulb has less wasted energy • This is shown by the smaller arrow downwards representing the heat energy BLESSING NDAZIE 58 ENERGY, WORK & POWER
- 59. Sankey diagrams for an energy efficient bulb and a filament bulb BLESSING NDAZIE 59 ENERGY, WORK & POWER
- 60. An electric motor is used to lift a weight. The diagram represents the energy transfers in the system. Calculate the amount of wasted energy. Worked Example BLESSING NDAZIE 60 ENERGY, WORK & POWER
- 61. Answer: BLESSING NDAZIE 61 ENERGY, WORK & POWER
- 62. Work Done BLESSING NDAZIE 62 ENERGY, WORK & POWER
- 63. Work done & energy transfers • Mechanical work is done when an object is moved over a distance by a force applied in the direction of its displacement • It is said that the force does work on the object • If a force is applied to an object but doesn’t result in any movement, no work is done • When work is done, energy is transferred • Work done and energy transferred are equivalent quantities BLESSING NDAZIE 63 ENERGY, WORK & POWER
- 64. Work done pushing a box Work is done when a force is used to move an object over a distance, and energy is transferred from the person to the box BLESSING NDAZIE 64 ENERGY, WORK & POWER
- 65. Work done equation BLESSING NDAZIE 65 ENERGY, WORK & POWER
- 66. Formula triangle for work done, force and distance • Mechanical work done and electrical work done are equivalent to energy transferred • work space done space equals space energy space transferred • Therefore: • 1 space straight N space straight m space equals space 1 space straight J BLESSING NDAZIE 66 ENERGY, WORK & POWER
- 67. Examples of work done • Work is done on a ball when it is lifted to a height: • A force is required to lift the ball • Work is done against the weight force to lift the ball through the gravitational field • Energy is transferred as work in done BLESSING NDAZIE 67 ENERGY, WORK & POWER
- 68. Work done by a bird • Work is done when a bird flies through the air • A force is required to overcome the drag force • Work is done against the drag force as the bird flies over a distance • Energy is transferred as work is done BLESSING NDAZIE 68 ENERGY, WORK & POWER
- 69. Worked Example A car moving at speed begins to apply the brakes. The brakes of the car apply a force of 500 N, which brings it to a stop after 23 m. Calculate the work done by the brakes in stopping the car. BLESSING NDAZIE 69 ENERGY, WORK & POWER
- 70. Answer: BLESSING NDAZIE 70 ENERGY, WORK & POWER
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- 72. Examiner Tips and Tricks • Remember to always convert the distance into metres and force into newtons so that the work done is in joules or newton-metres BLESSING NDAZIE 72 ENERGY, WORK & POWER
- 73. Power BLESSING NDAZIE 73 ENERGY, WORK & POWER
- 74. Power • Power is: • Work done per unit time • Since work done is equal to energy transferred, power is also: • Energy transferred per unit time • Machines, such as car engines, transfer energy from one energy store to another constantly over a period of time • The rate of this energy transfer, or the rate of work done, is power • Time is an important consideration when it comes to power • Two cars transfer the same amount of energy, or do the same amount of work to accelerate over a distance • If one car has more power, it will transfer that energy, or do that work, in a shorter amount of time BLESSING NDAZIE 74 ENERGY, WORK & POWER
- 75. Two cars with different power ratings doing the same amount of work Two cars accelerate to the same final speed, but the one with the most power will reach that speed sooner. BLESSING NDAZIE 75 ENERGY, WORK & POWER
- 76. Two motors with different powers •Two electric motors: • lift the same weight • by the same height • but one motor lifts it faster than the other • The motor that lifts the weight faster has more power BLESSING NDAZIE 76 ENERGY, WORK & POWER
- 77. Power ratings • Power ratings are given to appliances to show the amount of energy transferred per unit time • Common power ratings are shown in the table below: Appliance Power rating A torch 1 W An electric light bulb 100 W An electric oven 10 000 W = 10 kW A train 1 000 000 W = 1 MW Saturn V space rocket 100 MW Large power station 10 000 MW Global power demand 100 000 000 MW A star like the Sun 100 000 000 000 000 000 000 MW BLESSING NDAZIE 77 ENERGY, WORK & POWER
- 78. Calculating Power • The power equations • There are two equivalent forms of the power equation • Power can be expressed in terms of work done • Or power can be expressed in terms of energy transferred BLESSING NDAZIE 78 ENERGY, WORK & POWER
- 79. Worked Example Calculate the energy transferred when an iron with a power rating of 2000 W is used for 5 minutes. BLESSING NDAZIE 79 ENERGY, WORK & POWER
- 80. Answer: BLESSING NDAZIE 80 ENERGY, WORK & POWER
- 81. BLESSING NDAZIE 81 ENERGY, WORK & POWER
- 82. BLESSING NDAZIE 82 ENERGY, WORK & POWER
- 83. Examiner Tips and Tricks • Think of power as “energy per second”. Thinking of it this way will help you to remember the relationship between power and energy. • In your IGCSE exam, you will be expected to use both equations and to be able to rearrange them. You may be required to calculate the energy transferred in a previous question part, so always check back through the question if you seem to be missing a value! BLESSING NDAZIE 83 ENERGY, WORK & POWER
- 84. Efficiency BLESSING NDAZIE 84 ENERGY, WORK & POWER
- 85. Efficiency of energy transfer • The efficiency of a system is a measure of the amount of useful and wasted energy in an energy transfer • Efficiency is defined as: • The ratio of the useful power or energy output from a system to its total power or energy input • If a system has high efficiency, this means most of the energy transferred is useful • If a system has low efficiency, this means most of the energy transferred is wasted BLESSING NDAZIE 85 ENERGY, WORK & POWER
- 86. Efficiency of energy transfer • The overall efficiency of a typical thermal power station is approximately 30% • This means that 70% of the energy transferred from the power station to the National Grid is wasted energy • • In the production of electricity: • Energy is used to heat water to produce steam • The steam turns a turbine • The turbine turns a generator • The generator produces electricity • At each stage of this process, energy is dissipated to the surroundings BLESSING NDAZIE 86 ENERGY, WORK & POWER
- 87. Sankey diagram of electricity production Sankey diagram showing the energy transfers involved in generating electricity in a gas-fired power station BLESSING NDAZIE 87 ENERGY, WORK & POWER
- 88. Calculating efficiency • Efficiency is represented as a percentage, and can be calculated using two equations • Efficiency in terms of energy: BLESSING NDAZIE 88 ENERGY, WORK & POWER
- 89. Worked Example An electric motor has an efficiency of 35%. It lifts a 7.2 kg load through a height of 5 m in 3 s. Calculate the power of the motor. BLESSING NDAZIE 89 ENERGY, WORK & POWER
- 90. Answer: BLESSING NDAZIE 90 ENERGY, WORK & POWER
- 91. Answer: BLESSING NDAZIE 91 ENERGY, WORK & POWER
- 92. Worked Example 2 BLESSING NDAZIE 92 ENERGY, WORK & POWER
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- 96. Examiner Tips and Tricks • Efficiency can be given in a ratio (between 0 and 1) or percentage format (between 0 and 100 %) • If the question asks for efficiency as a ratio, give your answer as a fraction or decimal. • If the answer is required as a percentage, remember to multiply the ratio by 100 to convert it: • if the ratio = 0.25, percentage = 0.25 × 100 = 25 % • Remember that efficiency has no units BLESSING NDAZIE 96 ENERGY, WORK & POWER
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