1. P1 board notes

2. Stuff you know: What is the unit of temperature? What is the unit of heat energy? Which way does heat flow? Degrees Celsius (centigrade) The Joule From hot to cold

3. Stuff you know (2): What happens to hot things? What happens to cold things? Why? They cool down They heat up Heat flows into the surroundings or out of the surroundings So objects end up at room temperature.

4. Stuff you know (3): Does everything need the same energy to heat it up? What makes a difference? Why? No How big it is The bigger it is (more mass), the more energy it takes and different materials need different amounts of energy. What it’s made of

5. A Thermogram Eating an ice lolly The colours are added by computer The coldest areas are colour- coded in blue, the hottest in white.

6. Thermograms - uses A breast with cancer The warm one has the cancer A power switch overheating because of a poor connection Normal

7. This room has cold areas round the top of the window A heavy security fire door losing heat

8. Can-do: 39 – I can use a thermogram 9 – I can measure temp. in C 14 – I can calculate Sun exposure from SPF and health recommendations

9. Heating things up When you try to heat-up different materials, the amount of energy needed is different for every material. Metals need small amounts of heat energy, water needs a lot.

10. Heating a metal - 1 Collect an aluminium block, a timer, a thermometer, a power pack, 5 wires and a heater. Connect the heater to the power pack with an ammeter and voltmeter as shown Then put the heater in the block

11. Heating a metal - 2 Put the thermometer in the block Reset the timer. Take the starting temperature Turn on the power pack and start the timer. Heat for 5 minutes. Record the new temperature, you may need to wait a bit for it to settle.

12. Heating a metal - 3 Calculate the rise in temperature Calculate the electrical energy as: (volts x amps x time in seconds) This is the electrical energy in Joules Calculate how much heat energy it took per degree for the 1kg block (joules  temperature change in degrees) This is how much heat energy was needed per degree per kilogram.

13. Definition: The name for this value is specific heat capacity defined as: The amount of heat energy needed to raise the temperature of 1kg of a substance by 1°C Write-up the experiment.

14. Practice There is an equation for specific heat capacity: Energy =Mass xSpecific heat capacity x Change in temperature

15. Latent heat This is the energy change involved when 1 kg of a substance changes state – Melting / freezing Boiling / condensing Melting and boiling need heat energy, freezing and condensing release heat energy The energy change depends on which you are doing.

16. Can-do P2c - the energy transferred in a circuit

17. Insulation Heat can move by: Conduction (touching) Convection (warm gases / liquids moving) Radiation (heat “shining”)

18. Insulation has air- gaps in it Gases are poor conductors The insulation material stops air from moving around

19. The effect of insulation Take two metal beakers, one with insulation and one plain Put the same amount of hot water in each Take both temperatures every minute for 10 minutes Draw a graph of both temperatures

20. So how does heat travel? 3 key words: Conduction Convection Radiation

21. Conduction The particles in a hot material are vibrating and the vibration spreads to a colder material if they can touch. Gases and liquids are poor conductors because their particles are not strongly connected together.

22. Convection Heating-up part of a liquid or gas makes it expand, but it isn’t any heavier, so it rises above the cooler parts So hot air rises And so do all hot gases and liquids They will circulate if they have a chance.

23. How early coal mines were ventilated

24. Convection currents (Use overlay mode to draw currents)

25. Radiation “Heat travelling like light” “Infra-red” light rays Straight lines mean you can get heat shadows like light shadows Reflected like light, especially from light- coloured materials Absorbed best by dark/black materials “Shines-out” best from black materials

26. Says it all, really....

27. More infra-red Some other uses of infra-red radiation: Toaster (see it glow red) Iron (see it doesn’t glow red) Grill pan (heat energy absorbed by food) Remote controls for TVs etc.

28. The whole spectrum The spectrum we can see: is only a small part of the whole spectrum of electromagnetic waves:

29. Microwaves Microwaves are another form of radiation energy, like visible light and infra-red. They vibrate water molecules in the outer 20mm of food Vibration = heat The heat has to conduct to the rest of the food, so you usually stir it or rotate it. They do not really “cook from the inside”!

30. Or, used for mobile phones, Hazards: All forms of radiation are bad for you Microwaves have been connected to cell damage causing cancer

31. How different ovens cook (because it’s given people big problems!) Conventional Microwave Hot air circulates by convection Touches food, heat conducts into food outer surface Heat spreads through food by conduction and (sometimes) convection Microwaves vibrate water molecules This means they are hotter This heats the outer 1½ cm of food Heat spreads through food by conduction and (sometimes) convection

32. Ultraviolet and Sunburn Sunburn is caused by ultra-violet rays in sunlight U.V. damages living cells This is good for sterilising medical instruments or bacterial cultures It’s bad when it’s your skin Too much skin damage triggers skin cancer.

33. Sunscreen creams You need a physical barrier to stop the U.V. from reaching your skin Clothes, hats, sunscreen Sun protection factor, “how many times longer” you can stay in the Sun E.g. if you would normally burn after an hour, factor 10 cream will make that 10 hours You get different amounts and intensities of sunlight in different parts of the World.

34. Try these: If you would normally burn after ½ an hour in the sun, how long can you stay out when wearing: Factor 10 Factor 20 Factor 60 for sensitive skin Does everybody’s skin burn after the same time?

35. Beware! The numbers on the suncream bottle assume you have laid it on thickly Most people don’t.

36. The greenhouse effect The Sun sends out short-wave infra-red rays (high energy from a hot object) These come into the greenhouse through the glass Long wave infra-red (from cooler objects) is reflected back into the greenhouse by the glass and can’t get out So the greenhouse stays hotter than it should do

39. Global Warming Water vapour and carbon dioxide in the atmosphere have the same effect as the glass So the atmosphere traps heat and keeps us all warmer This is good unless… We have been making extra carbon dioxide from burning fossil fuels for the past 200 years, mostly in the last 40 years.

40. Probable Effects More extreme weather : Hot, wet countries get hotter and wetter (e.g. India – more floods, more dangerous) Hot dry countries get hotter and dryer (e.g. Australia – drought) England just gets warmer rain. (Crops rot in wet fields, cars rust faster) (and the lawn is too long and wet to cut with a mower.)

41. Efficiency Mostly of power stations, heaters, motors, hair dryers etc. Defined as useful energy obtained (x 100) total energy supplied (The x 100 is for a percentage, which is optional but makes some people more comfortable)