Properties of electromagnetic waves 1 — AQA GCSE Physics
Test yourself on Properties of electromagnetic waves 1 with AQA GCSE practice questions.
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Properties of electromagnetic waves 1 explained
This is Higher tier. Refraction is a change of direction caused by a change of speed.
Read the full explanation
An electromagnetic wave travels fastest in a vacuum and slows down in a material, and the more optically dense the material the slower it goes, so light travels more slowly in glass than in air. When a ray meets a boundary at an angle, one side of the wave enters the new material and slows before the other side does, so the whole wave swings round. Going from air into glass the wave slows and bends towards the normal; going from glass into air it speeds up and bends away from the normal. A ray arriving along the normal, at an angle of incidence of 0°, still changes speed but does not change direction, because both sides slow together.
Your focus
- Explain refraction at an air to glass boundary in terms of a change of wave speed.
- Predict whether a ray bends towards or away from the normal for a given pair of media.
- State which wave quantities stay the same and which change when a wave is refracted.
Properties of electromagnetic waves 1 exam tips
Marking Points
- one mark for stating that the wave changes speed when it enters a different substance
- one mark for saying it bends towards the normal when it slows down and away from the normal when it speeds up
- one mark for explaining that the change of direction is caused by the change of speed, not by the boundary itself
- one mark for saying that a ray travelling along the normal changes speed but not direction
Examiner Tips
- 💡Always name the direction relative to the normal: towards it or away from it.
- 💡Say which medium is the faster and which the slower before you state which way the ray bends.
- 💡Remember the frequency is set by the source and does not change at the boundary.
Common Mistakes
- saying light bends because the glass pushes it, with no mention of a change of speed
- claiming light speeds up in glass because glass is transparent
- bending the ray the wrong way as it enters a denser medium
- saying the frequency changes on refraction, when it is the speed and the wavelength that change