1.

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

Answer»

become zero
remain UNCHANGED
become INFINITE
none of these

Solution :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


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