1. Radiation and Evaporation
24/11/2018
Radiation and Evaporation
Objective
To describe the processes of heating and cooling by radiation and evaporation.

2. Observing Radiation
Before the lamp is switched on, move your hand around the side of the screen away from the lamp. Are there any differences in how hot the air or screen feels?
Get pupils to make a prediction. When the lamp is switched on, what will be the effect of the screen and the hole?

3. Words – sun, absorbs, nothing, warmer, waves
Radiation
When you wear a black t-shirt on a hot, sunny day you would feel ______ than if you wore white. This is because black ________ infrared radiation (i.e. heat) from the sun better than white does.
I’m cool!
I’m very hot!
Conduction is when heat travels through a solid and convection happens in a liquid or gas, but radiation can happen through absolutely ________ because the heat is moving by ______. This is how heat reaches us from the ____.
Words – sun, absorbs, nothing, warmer, waves

4. Evaporation
Heat can also be lost when a liquid evaporates (this is how we cool off when we sweat):
This water will evaporate because the water molecules have enough energy to “escape” from the rest of the water. When they do they will take heat with them.
Ensure that students understand that evaporation takes place even when a liquid is not boiling.
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5. Investigation Radiation
Use different coloured paper wrapped around 3 beakers to investigate radiation.
Fill each beaker with 75 ml of hot water.
Record the initial Temp.
After 1 min(s), record the temperature of the water in each beaker.
Repeat for 15 mins.
Which colour is the best emitter of heat?
Insert numbers into the blanks to set the number of different colours and the length of experiment. Discuss with the pupils the meaning of an emitter (how well it lets out energy), relating it to absorption of different colours from Slide 3. Extension: Plot the graph of the results individually or as a class.

6. Plenary/Extension
Write two things you have learnt today and one question you still have.