Question

83)the convex lens is placed in water. the focal length will _______

Answer 1

for convex lens ,
1/f = ( u -1) { 1/R1 - R2}

{ 1/R1 - 1/R2} is constant before and after
change ( u -1) part of this ,
becoz refractive index of medium change.


after sunmerged in water refractive index of lens wrt medium then, RF = u' < u


and focal length negative , becoz u'< 1
hence , answer is focal length will be negative It will be increases becoz ( u'-1) decreases , so, 1/f decreases so, f increases

Answer 2

Answer:

When a lens is placed in water,.. which has higher refractive index(1.33) then, air (1.003),. => Hence,the shape of the lens won't change when keeping that in water,. => ∴ There is no change in focal length of the lens,.

Explanation:

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