1. P1 Revision

2. Structure of P1 P1 is split into 5 different topics: 1.The transfer of energy by heating processes and the factors that affect the rate the energy is transferred 2.Energy and Efficiency 3.The usefulness of Electrical Appliances 4.Methods used to generate electricity 5.The use of waves for communication and to provide evidence that the universe is expanding.

3. Structure of P1 The P1 exam will test 3 different skills: 1.Recall – about 50% of the exam – use this PowerPoint and your revision guide to help, get others to test you 2.Application - 30% - go through past exam papers carefully 3.Analysis and Evaluation - 20% - go through past exam papers carefully

4. The Transfer of Energy by Heating Processes and the Factors that affect the rate of energy transfer

5. Infrared Radiation All objects Emit and absorb infrared radiation

6. Infrared Radiation Objects emit or absorb infrared radiation quickly if They have a big temperature difference with their surroundings They are Matt Black They have a big surface area

7. Infrared Radiation Objects emit or absorb infrared radiation slowly if They have a small temperature difference with their surroundings They are Silver or White They have a small surface area

8. Infrared Radiation Applications – cooling fins Matt black and large surface area means that it gets rid of heat quickly ( used to cool computer chips)

9. Kinetic Theory Solids are like ? : Ordered Rigid Structure ( Lattice) Vibrating atoms Strong bonds between them

10. Kinetic Theory Liquids are like ? : Swapping places Weaker bonds between atoms than solids Can’t compress but do flow

11. Kinetic Theory Gases are like ? : Random fast movement No bonds between them Can compress ( lots of spaces)

12. Energy Transfer by Heating Describe Conduction Metals are good conductors because they contain free electrons which carry Kinetic energy In all materials atoms also bump into each other when they vibrate more and so transfer Kinetic energy ( this is the only way that heat travels in an insulator)

13. Energy Transfer by Heating Describe Convection In convection the fluid is heated the particles move faster and further apart. The fluid is less dense and so rises.

14. Energy Transfer by Heating Describe Evaporation In evaporation the high energy molecules escape from the surface of the liquid and take energy away so the mean energy of the molecules is less so the liquid cools.

15. Energy Transfer by Heating Describe Condensation In condensation the molecules lose energy and the gas turns back into a liquid.

16. Energy Transfer by Heating How can we make something evaporate quickly ? Increase the surface area ( more particles exposed) Move air across the surface Make sure the air is dry

17. Energy Transfer by Heating Applications- vacuum flask

18. Energy Transfer by Heating Applications- House Insulation TRAPPED AIR STOPS CONVECTION

19. Pay Back time What is the pay back time ? The time it takes for the savings made to pay for the cost of the insulation.

20. Heating and Insulating Buildings What’s a U value ? The lower the U value the better the material is as an insulator.

21. Heating and Insulating Buildings What is Specific Heat Capacity? Is the amount of energy required to change the temperature of 1kg of a substance by one degree Celsius. 1°C rise

22. 1) A kettle contains 1.5kg of water at a temperature of 18ºC. How much energy is needed to bring the water to the boil? specific heat capacity of water is 4200J/kgºC E = m x c x θ = 1.5 x 4200 x 18 = 6000 J

23. 2) 50kJ of energy was transferred to a material with a mass of 5kg. The temperature increased from 20ºC to 60ºC. What is the specific heat capacity of the material? E = m x c x θ c = E / (m x θ) c = 50,000/ (5 x 40) = 250 J/kg/ o C

24. Energy & Efficiency

25. Energy and Efficiency What is special about energy? ENERGY CANNOT BE CREATED OR DESTROYED BUT IT CAN BE CHANGED FROM ONE FORM TO ANOTHER.

26. Energy & Efficiency What happens when energy is transferred ? When energy is transferred only part of it is transferred usefully, some of it is wasted.

27. Energy & Efficiency What happens to the wasted energy ? When energy is transferred to the surroundings they become warmer. The energy becomes more spread out and so less useful.

28. Efficiency A device isdescribed asefficientwhen a smallproportionof its energyis wasted What does it mean when a device is efficient ?

29. Calculating Efficiency Efficiency = Useful Energy Out x 100 Total energy in Total energy in x Efficiency = Useful Energy Out 100 Total energy in = Useful Energy Out x 100 Efficiency

30. Calculating Efficiency For every 70J of light energy that hits a solar cell 10.5J are converted to electricity. What is its efficiency ? Efficiency = Useful Energy Out x 100 Total energy in Efficiency = 10.5 x 100 = 15% 70

31. Calculating Efficiency 1)How efficient is a kettle when 150J of electrical energy supplied to it is converted to 100 J of heat energy in the water? Efficiency = Useful Energy Out x 100 Total energy in Efficiency = 100 x 100 = 67% 150

32. Calculating Efficiency 2) What total energy must have been supplied to a 60% efficient electric motor if it produces 150J of kinetic energy? Total energy in = Useful Energy Out x 100 Efficiency Total energy in = 150 x 100 = 250 J 60

33. Calculating Efficiency 3) What useful light energy will be obtained when 60J of electrical energy is supplied to a 25% efficient light bulb? Total energy in x Efficiency = Useful Energy Out 100 60 x 25 = 15 J 100

34. Sankey Diagrams Total Energy Input Useful Energy Wasted Energy Scale diagrams of energy transfers

35. Turning Text into Graphics 1)In an electric kettle for every 100J of electrical energy put in 80J heats the water and 20J is wasted and heats the surroundings. 10 Squares = 100J

36. Turning Text into Graphics 2) In a washing machine for every 160 J of electrical energy put in 50J is converted to Kinetic Energy and 100J is wasted.

37. Turning Text into Graphics 3) A team of scientists test a brand new hybrid car. It is 40 % efficient.

38. Efficiency

39. For every 100J of chemical energy in the petrol tank of a car 25 J of kinetic energy is produced

40. The usefulness of Electrical Appliances

41. Many household objects are designed to transfer energy from one form into another useful form. The Usefulness of Electrical Appliances electrical energy kinetic energy What energy transfer is an electric fan designed to carry out?

42. electrical energy sound energy What energy transfer are these speakers designed to carry out? The Usefulness of Electrical Appliances

43. Power is measured in kilowatts (kW) and the time is measured in hours (h), so what are the units of electricity measured in? 1 unit of electricity = 1 unit of electrical energy Example: How many units of electricity is 17.6 kWh? 17.6 units The amount of electrical energy (i.e. the amount of electricity) used by an appliance depends on its power and how long the electricity is used for. electrical energy = power x time = 1 kilowatt hour (kWh) The Usefulness of Electrical Appliances

44. Electricity costs money, which is why every home has an electricity meter. The units of electrical energy are called kilowatt hours (kWh). The cost of an electricity bill is calculated from the number of units used. The meter records how much electricity is used in a house in units of electrical energy. The Usefulness of Electrical Appliances

45. The cost of electricity is the number of units of electrical energy multiplied by the cost per unit. Example: How much would 10 units of electricity cost at a price of 9p per unit? cost = 10 units x 9 p/unit cost = number of units x cost per unit = 90 p The Usefulness of Electrical Appliances

46. A kettle uses 45.2 kWh of energy. If electricity costs 10 p per unit, how much does it cost to use the kettle? Number of units: Cost of electricity: = 45.2 units number of units of electricity = number of kilowatt hours = 452 p or £4.52 = 45.2 units x 10 p / unit cost = number of units x cost per unit The Usefulness of Electrical Appliances

47. An iron that operates at a power of 3 kW for 4 hours uses electricity that costs 8p per unit. How much does it cost for the electricity used by the iron in that time? Number of kWhrs: Cost of electricity : = 12 kWh = 3 kW x 4 h number of units of electricity = number of kilowatt hours = 96p = 12 kWhrs x 8 p cost = number of kWhrs x cost per unit The Usefulness of Electrical Appliances