Infrared
2 marks · EasyTwo identical beakers of water are placed at the same distance from an infrared lamp. Beaker 1 is covered with shiny foil, and Beaker 2 is covered with matte black paper. Both are left under the lamp for 5 minutes. Predict which beaker will be warmer at the end and explain why.
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Beaker 2 will be warmer because matte black surfaces absorb more infrared radiation than shiny surfaces.
Also accept: The black paper beaker will be warmer as dark, matte surfaces absorb infrared better than shiny ones.
Common mistakes: Beaker 1 will be warmer because shiny surfaces are better absorbers.; There is no difference.
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Marking points
B1 · 1 mark · Identifies that Beaker 2 (matte black) will be warmer.
B2 · 1 mark · Explains that matte black absorbs more infrared radiation.
Worked solution
Beaker 2 will be warmer because matte black surfaces absorb more infrared radiation, while shiny surfaces reflect it.