Two mirrors are inclined at an angle θ as shown in the figure. Light ray is incident parallel to one of the mirrors. Light will start retracing its path after third reflection if : (A) θ = 45° (B) θ = 30° (C) θ = 60° (D) all three
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The answer is 45 deg. (A).
The angle of incidence and reflection from first mirror = 90 - θ.
The angle of incidence on the second mirror = 2θ - 90.
If the ray has to retrace the path, then this angle must be 0. Then the ray will retrace to the point of incidence on the first mirror again and then further.
so θ = 45 deg.
The angle of incidence and reflection from first mirror = 90 - θ.
The angle of incidence on the second mirror = 2θ - 90.
If the ray has to retrace the path, then this angle must be 0. Then the ray will retrace to the point of incidence on the first mirror again and then further.
so θ = 45 deg.
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