Energy Transfers
3 marks · NormalOn a clear night, the temperature inside houses often drops even when windows and doors are closed and no air escapes.
Explain, using ideas of energy transfers, why the inside of the house cools down during a clear night.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
The inside of the house loses thermal energy to the outside by radiation. Warm surfaces inside the house emit infrared radiation, which passes through the windows to the cold night sky. As energy leaves the house by radiation, the temperature inside falls, even though no air escapes.
Must show: infrared radiation, energy leaves without air flow, temperature drop explained
Common mistakes: Saying conduction or convection from inside to outside only; Ignoring the effect of clear sky
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States thermal energy lost as infrared radiation.
B1 · 1 mark · Explains radiation can pass through windows to outside.
B1 · 1 mark · Temperature falls as energy leaves by radiation even though no draughts.
Worked solution
At night, surfaces inside the house release energy as infrared radiation. This radiation can travel through glass or escape through poorly insulated walls and roofs into the cold night sky. As the house emits more energy than it receives, the temperature inside drops.