Question

1. what is the focal length of concave lens whose refractive index = 1.5 , R1 = 30 cm , R2 = 30 cm ?

Answer 1

1/F=( n-1)×(1/R1-1/R2), here n=1.5 , R1= -30cm for concave lense and R2= +30 cm for concave lens , 1/F=( 1.5-1)× [-1/30-(1/30)] , 1/F = 0.5×(-1/30-1/30),. 1/F= 0.5×(-2/30),. 1/F= 1/2×(-1/30) , 1/F= -1/60, F= -60cm answer