Reflection of waves (physics only) — AQA GCSE Physics
Test yourself on Reflection of waves (physics only) with AQA GCSE practice questions.
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Reflection of waves (physics only) explained
A boundary is any place where the material a wave is travelling through changes: air to glass, air to a brick wall, water to the wall of a tank.
Read the full explanation
At every such boundary some of the wave bounces back into the first material, and that is reflection. The rule is the law of reflection: the angle of incidence equals the angle of reflection, both measured from the normal, the construction line drawn at 90° to the surface at the point where the ray strikes. A smooth surface such as a plane mirror sends a parallel beam back as a parallel beam, called specular reflection, so a clear image is seen. A rough surface scatters the rays in all directions because the normal points a different way at each point; this is diffuse reflection and no image forms, although the law still holds at every individual point. Sound reflects at boundaries too, which is why an echo returns from a wall.
Your focus
- State the law of reflection and identify the normal, the angle of incidence and the angle of reflection on a diagram of a plane mirror.
- Predict the direction of a reflected ray when an incident ray strikes a mirror at a given angle, measuring from the normal.
- Compare the beam reflected from a polished metal sheet with the beam reflected from a sheet of paper, using the direction of the normals.
Reflection of waves (physics only) exam tips
Marking Points
- one mark for stating that the angle of incidence is equal to the angle of reflection
- one mark for measuring both angles from the normal rather than from the surface of the mirror
- one mark for identifying the boundary as the place where the wave meets a second material
- one mark for distinguishing specular reflection from a smooth surface from diffuse reflection from a rough surface
Examiner Tips
- 💡Draw the normal first, as a dashed line at 90° to the surface; every angle in the answer is measured from it.
- 💡If a question says different materials, name both, for example air and glass, rather than writing at the surface.
- 💡Use the words specular and diffuse when the question shows a shiny and a matt surface side by side.
Common Mistakes
- measuring the angle between the ray and the mirror surface, so quoting 60° when the angle from the normal is 30°
- saying a rough surface does not obey the law of reflection, when it obeys it at every point but the normals point different ways
- assuming the whole wave is reflected, when some is usually transmitted or absorbed at the same boundary
- calling diffuse reflection refraction because the light appears to spread out