Students should be able to describe the effects of reflection,…

The idea

These questions give you a context and ask what the wave does at the interface and what follows from it. Work through the three outcomes in order. Reflection sends part of the wave back, giving an echo for sound or an image for light. Transmission lets part of it through into the second material, often with a change of speed and direction. Absorption transfers energy from the wave to the internal energy store of the material, warming it. Ozone high in the atmosphere is a good example: it absorbs all the UVC and nearly all the UVB, but none of the UVA, so the most strongly ionising ultraviolet never reaches the ground and the risk of skin damage is cut. A curtain absorbs and scatters light so a room darkens; foam lining a studio absorbs sound so echoes are reduced.

What earns the marks

• Saying that the ozone layer absorbs all of the UVC and nearly all of the UVB.
• Linking greater ionising power to greater risk of harm.
• Stating that UVA is not absorbed by ozone, so the ozone layer does not reduce the risk from UVA.
• Naming a consequence for people, such as damage to skin cells, sunburn or skin cancer.

Common mistakes and how to put them right

• Saying the ozone layer blocks all ultraviolet, when UVA passes straight through.

• Describing what the wave does but never naming the consequence the question asked for.

• Using reflected for light scattered from a matt surface without saying the surface is rough.

• Claiming absorbed waves are destroyed, rather than their energy being transferred to the absorber.

Exam tips

• These are often levels-marked questions, so write linked sentences that move from what the wave does to what a person notices.
• Quote figures from the graph or table you are given, such as 95% of UVB, to lift a level 1 answer to level 2.
• Use all three words, reflected, transmitted and absorbed, only when all three apply to the context given.