First slide

Ray optics

Question

Two plane mirrors are inclined at same angle $θ$ as shown in figure. A ray of light parallel to $M_{2}$ is incident on $M_{1} .$ After two successive reflections at the mirrors, the emergent ray becomes parallel to the mirror $M_{1} .$ Then the total angle of deviation of the ray is

Moderate

A

$172^{0}$
B

$240^{0}$
C

$270^{0}$
D

$150^{0}$

Solution

(2)
$\begin{array}{l} I n Δ O A B, 3 θ = 180^{0} \Rightarrow θ = 60^{0} \\ A t A, δ_{1} = 180^{0} - 60^{0} = 120^{0} (c l o c k w i s e) \\ A t B, δ_{2} = 180^{0} - 60^{0} = 120^{0} (c l o c k w i s e) \\ ∴ δ = δ_{1} + δ_{2} = 240^{0} (c l o c k w i s e) . \end{array}$

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