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Infrared radiation and surfaces. Here are three different coloured mugs of the same size. If we fill all three mugs with the same amount of water and leave them in the sun, which one will heat up quickest? .
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If we fill all three mugs with the same amount of water and leave them in the sun, which one will heat up quickest?
The black mug would heat up quickest because black is good at absorbing infrared radiation.
A dark surface is also a good emitter of radiation. A light shiny surface is a poor emitter of radiation.
The inside of a vacuum flask is silver to reduce infrared radiation and stop your drink heating up or cooling down too quickly.
This is a thermogram of a building. Why do you think the windows are red?
The three states of matter are solid, liquid and gas. Solids, liquids and gases are all made up of tiny particles.
• Fill in the table with a tick or a cross in every box. • Click to reveal the answers.
Expansion and contraction • Can you explain why the liquid in a thermometer expands when it gets hot and contracts when its cools down again?
Expansion joints • Large structures such as bridges have expansion joints. This allows them to expand and contract as the air temperature changes. What do you think would happen if they didn’t have them?
When you heat one end of an object, the particles start vibrating more. These particles collide with their neighbouring particles.
Heat energy is transferred through the solid by these collisions between the particles. This is called conduction.
Metals contain free electrons. These move through the metal and transfer the heat more quickly. Can you explain how the energy is transferred?
When gases transfer heat this is called convection. A radiator uses convection to heat a room.
The air nearest the radiator is heated, causing it to expand, become less dense, and rise. This is replaced by the cooler denser air. This movement is called a convection current.
Look at these two saucepans. How will evaporation affect how quickly the contents of the saucepans will heat up?
The particles with the most thermal energy will evaporate from the saucepan without a lid.
The saucepan with the lid stops these particles escaping and so its contents will heat up quickest.
This is why takeaway cups have lids. They are also made of a material which is a good thermal insulator. Both these things help to keep your drink warm and stop your hand burning when you hold it!
Look at the window behind this cooker. Can you explain why the glass is covered with condensation?
The gas which has evaporated from the saucepan, without the lid, touches the cool surface of the glass. The gas particles lose thermal energy and condense to form a liquid.
These two objects have the same volume but different surface areas. Which one will cool down more quickly and why?
The object with the larger surface area will cool down more quickly. The larger surface area allows more heat energy to be transferred to its surroundings.
These two objects are in different surroundings. Which one will cool down more quickly and why?
The object on the left will cool down more quickly because the temperature difference between it and its surrounding is greatest.
The spade on the left is made from plastic, whilst the spade on the right is made from metal. Which one will cool down more quickly and why?
The metal spade will cool down more quickly because it is a good thermal conductor. It can therefore also emit thermal energy more quickly to its surroundings.
Look at this radiator. Can you think of two elements in its design that help it transfer thermal energy?
Can you think of a way the transfer of thermal energy could be increased still further? Think about the colour of the radiator.
What method does this heat sink use to maximise thermal energy transfer?
It uses metal, which is a good thermal conductor and has a large surface area. Both these things help to transfer the energy away from the video card.
Look at this heat sink. How is thermal energy transfer being maximised even further?
