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Question

A crystal ball is 20 cm in diameter with R. I.=1.5. If a gypsy lady is 1.2 m from the ball, where is the image of the gypsy as seen from the other side?


A
6.9 cm from the crystal ball
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B
7.9 cm from the crystal ball
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C
8.9 cm from the crystal ball
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D
None of these
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Solution

The correct option is A 6.9 cm from the crystal ball
We have for refraction through a curved surface
μ2vμ1u=μ2μ1R


For refraction through surface (1)
1.5v1120=1.51+10(1)
v=36 cm

Image formed by surface (1) acts as a virtual object for surface (2).
Then, distance of virtual object from surface (2) =3620=16 cm

For refraction through surface (2),
1v1.5+16=11.510(2)
v=6.9 cm
Thus, final image is formed 6.9 cm to the right of the crystal ball.

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