Question

what is the focal length of double cancave lens kept in air with two sphercial surfaces of radii r1=30 and r2=60 cm take refractive index of lens n=15​

Answer 1

Answer:

R1=-30,R2=60,and also given lens is

in air so n=1.5

using 1/f=(1/R1-1/R2)

1/f=(1.5-1)[1/(-30)-1/60]

After solving

F=-40

Explanation:

Answer 2

Answer:

Using lens makers formula.

1/f =(μ−1)[1/R1-1/R2]

1/f=(1.5-1) [(1/-30) -1/60]

1/f=0.5×3/60

1/f=-0.5×1/20

f=-40