Three plane mirrors are placed as shown in the figure- A light ray striking the first mirror at an angle of incidence 60- after reflections at all the three mirrors- becomes opposite to the initial direction- Find the value of -Take angle of incidence to be equal at all the mirrors-

From geometry, 90^∘ i+θ +90^∘ r=180^∘ ⇒θ=i+r ⇒θ=2i=120^∘ [∵ i=r] ...

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Standard XII

Physics

Absorption of Light

Three plane m...

Question

Three plane mirrors are placed as shown in the figure. A light ray striking the first mirror at an angle of incidence $60^{\circ}$ , after reflections at all the three mirrors, becomes opposite to the initial direction. Find the value of $θ$ .

Take angle of incidence to be equal at all the mirrors.

60^{\circ}

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150^{\circ}

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120^{\circ}

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45^{\circ}

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Solution

The correct option is C $120^{\circ}$

From geometry,

$90^{\circ} - i + θ + 90^{\circ} - r = 180^{\circ}$

$\Rightarrow θ = i + r$

$\Rightarrow θ = 2 i = 120^{\circ} [∵ i = r]$

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Three plane mirrors are placed as shown in the figure. A light ray striking the first mirror at an angle of incidence 60∘, after reflections at all the three mirrors, becomes opposite to the initial direction. Find the value of θ. Take angle of incidence to be equal at all the mirrors.

The correct option is C 120∘ From geometry, 90∘−i+θ+90∘−r=180∘ ⇒θ=i+r ⇒θ=2i=120∘ [∵i=r]

The correct option is C $120^{\circ}$

From geometry,

$90^{\circ} - i + θ + 90^{\circ} - r = 180^{\circ}$

$\Rightarrow θ = i + r$

$\Rightarrow θ = 2 i = 120^{\circ} [∵ i = r]$