Physics
Two mirrors are placed at right angles to each other as shown in the figure given below. A ray of light PQ strikes mirror OM at an angle of incidence 30°. What would be its angle of reflection from mirror ON ?
- 30°
- 60°
- 45°
- 90°
Reflection of Light
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Answer
60°
Reason — From below figure,
Reflection from mirror OM :
Angle of incidence = 30°,
So by law of reflection,
Angle of incidence = Angle of reflection = 30°
This means the reflected ray QR (say) makes an angle of 30° with the normal to OM, i.e., 60° with mirror OM. Now ray QR moves toward mirror ON, since OM and ON are at 90° and QR makes 60° with OM then it must make 90° - 60° = 30° with mirror ON.
So, angle between incident ray and normal to ON = 60°
⇒ Angle of incidence at ON = 60° = Angle of reflection
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