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Q. A light ray is incident on a plane mirror, which after getting reflected strikes another plane mirror, as shown in figure. The angle between the two mirrors is 60°. Find the angle 'θ' shown in figure.
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Asked by akku725005 | 12 Jul, 2019, 21:34: PM
answered-by-expert Expert Answer
Figure shows two plane mirrors kept at angle 60°.  A light ray incidents at A making an angle of incidence α,
reflected and again incidents at B making an angle β and getting reflected .
Reflected ray from B makes angle θ with the initial incident ray.
 
At reflection point A, as shown in figure, we have α+x = 90° ..............(1)
At reflection point B, as shown in figure, we have β+y = 90° ..............(2)
 
By adding (1) and (2), after substituting x+y = 120°, we get,  α+β = 60° ...............(3)
 
From ΔABC, we have,  2α + 2β + θ = 180° ...................(4)
 
Hence By using eqn.(3), we get , θ = 180 - 120 = 60°
Answered by Thiyagarajan K | 12 Jul, 2019, 22:42: PM

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