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A glass or glycerin convex lens of refra...

A glass or glycerin convex lens of refractive index `3//2` has got a focal length equal to 50 cm. Find the focal length of the lens, if it is immersed in ethyl alcohol of refractive index 1.36.

Text Solution

Verified by Experts

According to lensmakers formula,
`(1)/(f)=((mu_(2))/(mu_(1))-1)((1)/(R_(1))-(1)/(R_(2)))`
`rArr (1)/(f)= (1.5-1)((1)/(R_(1))-(1)/(R_(2)))` (i)
In ethyl alcohol, `(1)/(f_(" liquid "))=((1.5)/(1.36)-1)((1)/(R_(1))-(1)/(R_(2)))` (ii)
Dividing (i) and (ii), we get
`(f_(" liquid "))/(f)=((1.5-1)((1)/(R_(1))-(1)/(R_(2))))/(((1.5)/(1.36)-1)((1)/(R_(1))-(1)/(R_(2))))`
`rArr f_("liquid")=242.75cm`
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