A ray parallel to principal axis is incident at 30∘ from normal on concave mirror having radius of curvature R. The point on principal axis where rays are focussed is Q such that PQ is
A
R2
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B
R√3
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C
2√R−R√2
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D
R(1−1√3)
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Solution
The correct option is DR(1−1√3) From similar triangles, QCsin30∘=Rsin120∘ or QC=R×sin30∘sin120∘=R√3 Thus PQ=PC−QC=R−R√3=R(1−1√3).