CBSE Class 12-science Answered

The relation between the focal length, f, and radius of curvatures R ₁ and R ₂ is given by the lens makers formula. The lens maker formula for concave lens is,

where µ is the refractive index of the material of the lens.

where R1 and R2 are negative for concave surfaces.

 for diverging lens

1/f= ( ?-1)[-1/R -1/R] Thus, f= -R/[2( ?-1)]
For each plano concave lens:

1/f' = ( ?-1)[-1/R -1/?]

Thus    f'= -R/[( ?-1)].

Hence f' =2 f.

The focal length of each half part will be twice the focal length of diverging lens.