JEE Main · 2022 · 26 Jun 2022 · Shift 1 · Geometrical Optics

A light ray is incident, at an incident angle

θ_{1}

, on the system of two plane mirrors

M_{1}

and

M_{2}

having an inclination angle

7 5^{\circ}

between them (as shown in figure). After reflecting from mirror

M_{1}

it gets reflected back by the mirror

M_{2}

with an angle of reflection

3 0^{\circ}

. The total deviation of the ray will be ____ degree.

Answer: 210

Solution

For two plane mirrors inclined at angle

θ

, the total deviation after two reflections is given by

δ_{total} = 36 0^{\circ} - 2 θ

.

Given

θ = 7 5^{\circ}

δ_{total} = 36 0^{\circ} - 2 \times 7 5^{\circ} = 36 0^{\circ} - 15 0^{\circ} = 21 0^{\circ}

Alternatively, by tracing the ray path and summing individual deviations at each reflection, the total deviation is 210°.

JEE Main · 2022 · 26 Jun 2022 · Shift 1 · Integer answer

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