Two plane mirrors are kept on a horizontal table making an angle θ with each other as shown schematically in the figure. The angle θ is such that any ray of light reflected after striking both the mirrors return parallel to its incident path. For this to happen, the value of θ should be

Question

Two plane mirrors are kept on a horizontal table making an angle θ with each other as shown schematically in the figure. The angle θ is such that any ray of light reflected after striking both the mirrors return parallel to its incident path. For this to happen, the value of θ should be, 30 °, 45 °, 60 °, 90 °

MARKS App · Accepted Answer

As emergent ray is parallel to incident ray, deviation angle δ is 180 ° But δ = 360 ° - 2 θ where, θ = angle between inclined mirrors. . So, 360 ° - 2 θ = 180 ° or 2 θ = 180 ° ⇒ θ = 90 °

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