1. Year 10 Science
Heat and energy

2. Evaporation and radiation

3. Evaporation

4. Evaporation
Evaporation occurs when faster moving particles break free of the surface of a liquid and become gas particles.
The liquid left behind has less energy and becomes cooler.

5. Evaporation and boiling
Evaporation can occur at any temperature, but only at the surface of a liquid.
Boiling occurs at a single temperature, but can occur anywhere in a liquid.

6. Water cycle
The Sun’s radiation causes evaporation of water from land, rivers and the sea.
This evaporation drives the water cycle.

7. Radiated heat
The heat is carried away from the hot object by an electromagnetic wave called infra red.
Infra red radiation lies just outside the red end of the visible light that we can see.
It is identical to light except it has a slightly longer wavelength.
Infra red radiation can travel through a vacuum.

8. Solar Radiation: Sun to Earth
Speed of light = 300,000 km/s.
(186,000 miles/sec)
Distance to Earth: 150 million km (93 million miles).
Radiation reaches us from the Sun in about 8.3 minutes.
Only radiation can travel through the vacuum of space.

9. Sun’s electromagnetic spectrum -

10. Infra red
Ultra violet

11. All objects emit radiation.
Radiation Laws
All objects emit radiation.
more radiation
less radiation
Hot objects emit more radiation (per unit area) than cold objects.

12. How much do you radiate ? 500 W 50W 5 W .5 W
Incredible! – That’s a fridge and computer!
That’s why a space blanket works so well!

13. Emitting Radiated Heat
More heat is emitted from hot objects.
Dark colours are good emitters of heat.
Dull colours are good emitters of heat.
Bright colours are bad emitters.
Shiny colours are bad emitters.

14. Investigating radiation
Aim:
To investigate if the colour of a can will affect the rate at which it cools.
Apparatus:
Three cans of identical size and mass, thermometers, a kettle, a timer and a stand to hold the thermometers.

15. Method Arrange your cans and thermometers next to one another.
Boil some water in the kettle.
Pour the same amount of water into the cans, being careful not to spill any water onto the outside of the cans.
Record the temperature of the cans every 30 seconds for 10 minutes.
Draw a graph of your results when you have finished.

16. Table of results Time (mins) Temp. of water in shiny can (C)
Temp of water in white can (C)
Temp. of water in dull black can (C)
100 1 2 3
etc 10

17. Emitting radiation Fridge heat exchangers are painted matt black,
Tea urns are polished aluminium,
Fire backs are matt black,
Electric fires often have polished reflectors.
Car radiators are painted black.

18. Good Reflectors
Buildings in the Mediterranean are often painted white. This is because white surfaces are good reflectors of the heat radiation. This means that during the day it helps to keep the insides of buildings as cool as possible by reflecting heat radiation away from the building.

19. Good Reflectors
Teapots are often shiny. This is because shiny surfaces are good reflectors of heat radiation. The shiny surface of the teapot will therefore reflect any heat radiation trying to escape from the teapot back in. This means any tea poured into the teapot will stay warmer for longer.

20. Radiation: Light carries energy!

21. This is a “Thermos” or Vacuum flask.
Hot tea
Outer
Case
Stopper
Vacuum
Air space
It has a double lining inside the case, that contains a vacuum.
How does a Vacuum flask manage to keep hot things hot for longer than a regular bottle?

22. The stopper prevents heat escaping by convection.
The vacuum prevents heat escaping by conduction.
The inner flask is reflective inside, so it reduces heat lost by radiation.
The outer case protects the inner flask, and adds another layer of insulation.

23. Radiation summary
_________ is the only method of heat transfer that can travel through a _______.
Radiation
vacuum
Heat radiation is emitted by any body with a ___________ above absolute zero.
temperature
Heat radiation is a type of ______________ radiation. Like all electromagnetic radiation it travels in _______ lines and at the speed of _____.
electromagnetic
straight
light
Bodies that give out heat radiation are known as emitters. Dull, ______ surfaces are the best surfaces for emitting radiation.
black
Bodies that take in heat radiation are known as absorbers. Dull, black surfaces are the best surfaces for absorbing radiation.
Shiny, _____ surfaces are very good at _________ heat radiation.
white
reflecting

24. The big picture Works in Solids Fluid (Liquid, Gas) Vacuum Conduction
Convection
Radiation

25. Solids Works in Solids Fluid (Liquid, Gas) Vacuum Conduction YES
Convection NO
Radiation
YES (?)

26. Liquids Works in Solids Fluid (Liquid, Gas) Vacuum Conduction YES
Convection NO
Radiation
NO/Yes

27. Gases Works in Solids Fluid (Liquid, Gas) Vacuum Conduction YES NO
Convection
Radiation
NO/Yes