Question

# An object starts moving at an angle at with the principal axis as shown in fig in front of a biconvex lens of focal length . If denotes the angle at which image starts to move with principal axis, then:

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D
Hard
Solution
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Correct option is D)

## ; So, from , we get: Magnification: ............ (i) Hence vertical velocity of image is same as that of object but in reverse direction. Let the horizontal velocity be We have: Differentiating w.r.t. time, we get: [using (i)] Hence angle made by velocity vector of image is

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