30th April 2015

LO: To understand what affects energy transfer by radiation

Radiation

STARTER:If conduction and convection need particles to transfer heat energy, how does the heat energy from the Sun travel across Space to reach the Earth?

https://www.youtube.com/watch?v=3DUzw6xhmBo

Challenge! Which will cool fastest?

1. Working with the person sitting next to you.2. Take 4 boiling tubes. Fill each with the same

volume of hot water. 3. Wrap one in black paper. One in white

paper. One in silver foil. Leave one with no wrapping.

4. Record their temperatures. 5. Start timer.6. Which do you think will lose the most heat in

10 minutes?7. Write a prediction, explaining why you think

this.8. Record their temperatures after 10 minutes.

9. Was you prediction correct? Why?/Why not?

Class Results

Material Temperature loss after 10 minutes ( ْC)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Av

Black paper

White paper

Foil

No wrapping

Are there any anomalous results?

Can you think of any explanations for any anomalous results?

Can you explain the results using the terms absorber and emitter?

How does this type of imaging work?

Call of Duty

Earth & The Sun• The Earth is warmed by heat energy from the Sun –

how does it get here?!

There are no particles between the Earth and the Sun, so the heat cannot travel by conduction or convection

Instead the heat travels to Earth via infrared waves – similar to light waves (with a longer wavelength), travelling at 300’000kmsec-1 (like any wave they can be reflected and absorbed)

Radiation• In radiation, radiant energy (infra-red) is

emitted by a hot object and absorbed by another cooler object.

• All hot objects radiate heat to the surroundings via infra-red waves – this heat radiation does not need particles, so it means heat can travel through a vacuum.

Radiation

• All objects emit (give out) some thermal radiation

• Some surfaces are better at emitting thermal radiation than others…

Matt black surfaces are the best emitters of radiation

Shiny surfaces are the worst emitters of radiation

What would happen if you were to repeat the experiment with cold

water?

Radiation

• Infrared waves heat objects that absorb (take in) them

• Some surfaces are better at absorbing thermal radiation than others – good emitters are also good absorbers

Matt black surfaces are the best absorbers of radiation

Shiny surfaces are the worst absorbers because they reflect most of the radiation away

Leslie Cube• A Leslie cube is a

device that has sides made from different materials.

• It is filled with hot water and the energy emitted from each side is measured.

• Can you explain which side will record the highest temperature? Use the terms absorber and emitter.

Homework(write this in your

planner)• Due in on Thursday 7th May• Explain the three methods of heat transfer

Quiz