Question

The focal length of an equiconvex lens is 1.00m when it is placed under water . calculate the focal length of the same lens in air.Take the refractive indices if water and glass as4/3 and3/2 respectively.​

Answer 1

Answer:

if water and glass.respectively

Answer 2

The focal length of equiconvex lens is 20 cm

1/f=(μ−1)( 1/R1 - 1/R2 )

for equiconvex lens R1=−R2=R

thus,

1/20=(μ−1)( 1/R+1/R)

⇒R=40(μ−1)

when lens is cut into two equal parts perpendicular to optical axis

then,

R1=∞,R2=R

thus

1/f'=(μ−1)( 1/R1 - 1/R2)

1/f'=(μ−1)( 1/R )

by putting value of R we get,

1/f'=(μ−1)( 1/40(μ−1)

1/f'=40cm