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Explain what happens when a convex lens ...

Explain what happens when a convex lens of refractive index `1.2` is immersed in a liquid of refractive index `1.3`.

Text Solution

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If `f` is focal length of the lens of
`mu = 1.2`, then from `(1)/(f) = (mu -1)((1)/(R_(1)) - (1)/(R_(2)))`
`= (1.2 -1)((1)/(R_(1)) - (1)/(R_(2)))`
`:. (1)/(R_(1)) - (1)/(R_(2)) = (1)/((0.2)f)` …(i)
Let `f'` be focal length of this lens, when immersed in a liquid of refractive index `mu' = 1.3`.
`:. (1)/(f') = ((mu)/(mu') - 1)((1)/(R_(1)) - (1)/(R_(2)))`
`(1)/(f') = ((1.2)/(1.3) -1) xx (1)/((0.2)f) = -(1)/(13 xx 0.2 f)`
`f' = -2.6 f`
The lens will behave as concave lens and its focal length will be `2.6` times the initial focal length.
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