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Reflection of Light (Cambridge O Level Physics)
Revision Note
Ray Diagrams
- Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary
- The angle of the wave approaching the boundary is called the angle of incidence (i)
- The angle of the wave leaving the boundary is called the angle of reflection (r)
- The line at right angles (90°) to the boundary is known as the normal
- When drawing a ray diagram an arrow is used to show the direction the wave is travelling
- An incident ray has an arrow pointing towards the boundary
- A reflected ray has an arrow pointing away from the boundary
- The angles of incidence and reflection are usually labelled i and r respectively
Reflection
A ray diagram for light reflecting at a boundary, showing the normal, angle of incidence and angle of reflection
The Law of Reflection
- The law of reflection states that these angles are the same:
Angle of incidence (i) = Angle of reflection (r)
Law of Reflection
Reflection of a wave at a boundary, i = r
Examiner Tip
When drawing light waves being reflected take care to get the angles equal.
If they are slightly out it won’t be a problem, but if there is an obvious difference between the angle of incidence and the angle of reflection then you will lose a mark. Use a protractor to be sure of the angles.
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