One end of a cylindrical glass rod shown in figure ends in a hemispherical surface of radius R = 20 mm. Let the same rod be immersed in water of index 1.33, the other quantities having the same values as before. Find the image distance.
A
120 mm
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B
-120 mm
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C
180 mm
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D
-180 mm
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Solution
The correct option is D -180 mm
1.5v−1.33−80=1.5−1.3320,v=−180mm. The fact that v is negative means that the rays, after reflection by the surface are not converging but appear to diverge from a point 180 mm to the left of the vertex. In this illustration, then the surface forms a virtual image 180 mm to the left of the vertex.