Question

When the convex lens placed in water its focal length will ______(increase/decrease)?

Answer 1

 
   When a lens is placed in water,.. which has higher refractive index(1.33) then, air (1.003),.

=>focal length is the half of length of radius of the given curvature,.($f= \frac{R}{2}$)

=> Hence,the shape of the lens won't change when keeping that in water,.


          => ∴  There is no change in focal length of the lens,.