Question

A dpuble convex lens has two surface of equal raddii R and refractive index 1.5 then focal length is

Answer 1

Answer: 1/f=(n-1)(1/R1+1/R2)

n=1.5

R1=R2=R

1/f=(1.5-1)(1/R+1/R)

1/f=(0.5)(1+1/R)

1/f=1/2(2/R)

1/f=1/R

f=R