Question

Two plane mirrors P and Q are aligned parallel to each other, as shown in the figure. A light ray is incident at an angle of θ at a point just inside one end of A. The plane of incidence coincides with the plane of the figure. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is

• A. $\frac { l } { d \tan \theta }$
• B. $\frac { d } { l \tan \theta }$
• C.
• D. None of these

Answer 1

Answer: (A)

$\frac { l } { d \tan \theta }$

Answer 2

Suppose n = Total number of reflection light ray undergoes before exist out.

x = Horizontal distance travelled by light ray in one reflection.

So nx = l also $\tan \theta = \frac { x } { d }$

$\Rightarrow \quad n = \frac { l } { d \tan \theta }$