1.

A light ray is incident on a horizontal plane mirror at an angle of 45^(@). At what angle should a second plane mirror be placed in order that the refelcted ray finally be reflected horizontally form the second mirror, as shown in figure

Answer»

`theta=30^(@)`
`theta=24^(@)`
`theta=22.5^(@)`
`theta=67.5^(@)`

Solution :(c) From figure `CD=` emergent ray and `CD` is parallel to `PQ` and `BC` is a line intersecting these parallel lines,
So, `/_DCB/_CBQ=180^(@)`
`/_DCN+/_NCB+/_CBQ=180^(@)`
`alpha+alpha+45^(@)=180^(@)`
`alpha=67.5^(@)`
But `/_NCS=90^(@)`
So, SECOND mirror is at an ANGLE of `22.5^(@)` with horizontal .


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