Heating And Cooling Lesson 5

Thermal radiationThermal radiation

Target

To know how radiation of heat takes place

Monday 10 April 2023

What is this?What is this?

Shower – red where water is

hottest

What is this?What is this?

Pylons – red where they are

hottest

What is this?What is this?

Car – red where wheels are hottest

due to braking

What is this?What is this?Car park – white where there are warm objects – people and cars

What is this?What is this?

What is this?What is this?

What is this?What is this?

What is this?What is this?

What is this?What is this?

Thinking taskThinking task

• Look at the picture of a man running away from an exploding volcano.

• Why is he dressed in the white suit?

What is radiation of heat?What is radiation of heat?

• Heat is radiated by any hot object as INFRA RED waves – they pass through air or a vacuum – they cannot be seen

Good radiators of heatGood radiators of heat

• Black (or dark) coloured objects radiate heat best.

• A motorcycle with the black engine cools faster than one with a silver engine!

Good absorbers of radiation heatGood absorbers of radiation heat

• Black (or dark) colours also absorb radiation heat best.

• So dark surfaced objects quickly become warmer.

QuestionsQuestions 1. What do light rays and infra red rays have in common?

2. Why is this boy feeling so hot?

3. Why is the man wearing a white suit for the space walk?

Light rays and infra red rays travel at the speed of light.

Wearing black clothes make a person feel hot because black absorbs infra red waves very well.

White suits reflect heat so they reflect sunlight during a walk in space.

More questionsMore questions4. What colour should the inside of a

cooler box be made? Explain your answer.

5. Why does the tar melt on the road on a summers day?

6. Why do people living in hot countries often paint their houses white?

7 Solar panels are usually black in colour – what is the reason for this?

Cooler boxes should be white or silver to stop heat being absorbed.

Tar on the road melt on a hot summer because black absorbs heat very well.

Houses in hot countries are painted white to reflect light and heat waves and keep the house cool.

Solar panels are painted black to absorb light and heat wave so they warm the water in the pipes.