Types of Energy

1. Types of Energy Heat Chemical Light Gravitational Sound Elastic/strain Kinetic Nuclear Electric Stored/potential

2. The Law of Conservation of Energy Energy can be changed (transformed) from one type to another, but it can never be made or destroyed.

3. This means that the total amount of energy in the Universe stays the same!

4. Energy Flow diagrams We can write energy flow diagrams to show the energy changes that occur in a given situation. For example, when a car brakes, its kinetic energy is transformed into heat energy in the brakes. Kinetic heat sound

5. Other examples When a rocket launches. Chemical kinetic gravitational heat heat sound

6. Energy degradation! In any processthat involves energytransformations, the energythat is transferred to the surroundings (thermalenergy) is no longer available to perform usefulwork.

7. Energy transfer (change) A lamp turns electrical energy into heat and light energy

8. Sankey Diagram A Sankey diagram helps to show how much light and heat energy is produced

9. Sankey Diagram The thickness of each arrow is drawn to scale to show the amount of energy

10. Sankey Diagram Notice that the total amount of energy before is equal to the total amount of energy after (conservation of energy)

11. Efficiency Although the total energy out is the same, not all of it is useful.

12. Efficiency Efficiency is defined as Efficiency = useful energy output total energy input

13. Example Efficiency = 75 = 0.15 500

14. Energy efficient light bulb Efficiency = 75 = 0.75 100 That’s much better!

15. Energy Density • The energy that can be obtained from a unit mass of the fuel • J.kg-1 • If the fuel is burnt the energy density is simply the heat of combustion

16. Energy density • Coal - 30 MJ.kg-1 • Wood - 16 MJ.kg-1 • Gasoline – 47 MJ.kg-1 • Uranium – 7 x 104 GJ.kg-1 (70000000 MJ.kg-1)

17. Hydroelectric energy density? • Imagine 1 kg falling 100m. • Energy loss = mgh = 1x10x100 = 103 J • If all of this is turned into electrical energy it gives an “energy density” of the “fuel” of 103 J.kg-1

18. Electromagnetic induction If a magnet is moved inside a coil an electric current is induced (produced)

19. Electromagnetic induction A electric current is induced because the magnetic field around the coil is changing.

20. Generator/dynamo A generator works in this way by rotating a coil in a magnetic field (or rotating a magnet in a coil)

21. Non-renewable • Finite (being depleted – will run out) • In general from a form of potential energy released by human action

22. Fossil fuels – Coal, oil, gas

23. Nuclear fuels

24. Renewable • Mostly directly or indirectly linked with the sun • The exception is tidal energy

25. Photovoltaic cells (photoelectric effect)

26. Active solar devices

27. Wind

28. Wave

29. Tidal

30. Biomass

31. World energy production

32. Electricity production Generally (except for solar cells) a turbine is turned, which turns a generator, which makes electricity.

33. Fossil fuels In electricity production they are burned, the heat is used to heat water to make steam, the moving steam turns a turbine etc.

34. Fossil fuels - Advantages • Relatively cheap • High energy density • Variety of engines and devices use them directly and easily • Extensive distribution network in place • Gas power stations are about 50% efficient

35. Fossil fuels - Disadvantages • Will run out (finite) • Burning coal can cause acid rain • Oil spillages etc. • Contribute to the greenhouse effect by releasing carbon dioxide

36. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • Calculate the rate at which thermal energy is provided by the coal Efficiency = useful power output/power input Power input = output/efficiency Power input = 400/0.35 = 1.1 x 103 MW

37. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • Calculate the rate at which coal is burned (Coal energy density = 30 MJ.kg-1) 1 kg of coal burned per second would produce 30 MJ. The power station needs 1.1 x 103 MJ per second. So Mass burned per second = 1.1 x 103/30 = 37 kg.s-1 Mass per year = 37x60x60x24x365 = 1.2 x 109 kg.yr-1

38. A coal powered power plant has a power output of 400 MW and operates with an overall efficiency of 35% • The thermal energy produced by the power plant is removed by water. The temperature of the water must not increase by moe than 5 °C. Calculate the rate of flow of water. Rate of heat loss = 1.1 x 103 – 0.400 x 103 = 740 MW In one second, Q = mcΔT 740 x 106 = m x 4200 x 5 m = 35 x 103 kg So flow needs to be 35 x 103 kg.s-1

39. Nuclear Fission

40. Uranium Uranium 235 has a large unstable nucleus.

41. Capture A lone neutron hitting the nucleus can be captured by the nucleus, forming Uranium 236.

42. Capture A lone neutron hitting the nucleus can be captured by the nucleus, forming Uranium 236.

43. Fission The Uranium 236 is very unstable and splits into two smaller nuclei (this is called nuclear fission)

44. Free neutrons As well as the two smaller nuclei (called daughternuclei), two neutrons are released (with lots of kinetic energy)

45. Fission These free neutrons can strike more uranium nuclei, causing them to split.

46. Chain Reaction If there is enough uranium (critical mass) a chain reaction occurs. Huge amounts of energy are released very quickly.

47. Bang! This can result in a nuclear explosion!YouTube - nuclear bomb 4

48. Controlled fission The chain reaction can be controlled using control rods and a moderator. The energy can then be used (normally to generate electricity).

49. Fuel rods • In a Uranium reactor these contain Enriched Uranium (the percentage of U-235 has been increased – usually by centrifuging)

50. Moderator This slows the free neutrons down, making them easier to absorb by the uranium 235 nuclei. Graphite or water is normally used. 1 eV neutrons are ideal)