A small hole P is made in a piece of cardboard. The hole is illuminated by a torch as shown in Fig. The pencil of light coming out of the hole falls on a mirror. At which point should the eye be placed so that the hole can be seen?

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Solution

Law of reflection
According to the law of reflection, we know that in a plane reflecting surface, the angle of reflection and the angle of incident is equal.
So, $A n g l e o f i n c i d e n t (i) = A n g l e o f r e f l e c t i o n (r)$
Angle of the incident is the angle between the surface normal and incident light. It is the same as the reflection angle.
So, after reflection from the mirror the light rays will reach at point A.
Diagram
Therefore, from point A the hole can be seen.

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