Question

What is the focal length of double concave lens kept in air with two spherical
surfaces of radii R1 = 30cm and R2=60cm. Take refractive index of lens as n = 1.5.

Answer 1

Answer:

f=-40cm

pls mark me as BRAINLIEST

Answer 2

Answer:

answer will be 40 or -40

Explanation:

1) answer

according to sign convention

R1=30

R2= -60

n=1.5

f=?

from lens makers formulae

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

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

1/f=0.5 (1/30+1/60)

1/f=1/2 (60+30/1800)

1/f=1/2 (90/1800)

1/f=1/2 (1/20)

1/f=1/40

f=40cm

2)answer

R1= -30

R2= 60

n=1.5

f=?

from lens makers formulae

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

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

1/f=0.5 (-1/30-1/60)

1/f=0.5 (-60-30/1800)

1/f=0.5 (-90/1800)

1/f=0.5 (-1/20)

1/f=1/2 (-1/20)

1/f=1/-40

f= -40cm