if a glass lens is immersed in oil what is the effect on focal length of lens
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Given: A glass lens immersed in oil.
To find: Effect on focal length of lens
Explanation: Let the refractive index of lens be ug and refractive index of oil be uo.
The formula for focal length of lens is:
where r1 and r2 is the radius of the two surfaces of the lens.
Now, when glass lens is kept in air the term ug/uo becomes smaller as compared to 1. Therefore, the term becomes negative. So, the lens starts showing opposite properties. The convex lens which has a positive focal length becomes negative(diverging) and concave lens which has negative focal length becomes positive(converging) .
Therefore, the properties of glass lens change from diverging to converging and vice versa when it is immersed in oil.