A convex lens is immersed in a liquid, whose refractive index is equal to the refractive index of the material of the lens. Then its focal length will

Options

A. become zero
B. remain unchanged
C. become infinite
D. none of these

Answer

B, C

Explanation

Focal length in liquid,
`(1)/(f_L)=((n_g)/(n_L)-1)((1)/(R_1)-(1)/(R_2))`
`n_g=n_L`
`therefore (1)/(f_L)=(1-1)((1)/(R_1)-(1)/(R_2))`
`therefore (1)/(f_L)=0`
`therefore f_L`=Infinite