Question

Calculate the focal length and the power of a lens if the radii of curvature of its two surfaces are +20cm and –25cm (μ = 1.5).

Answer 1

Dear Student,

◆ Answer -

P = 4.5 D

f = 22.22 cm

● Explanation -

# Given -

R1 = +20 cm = 0.2 m

R2 = -25 cm = 0.25 m

# Solution -

Power of lens is calculated by formula -

P = (μ-1) (1/R1 - 1/R2)

P = (1.5-1) (1/0.2 - 1/-0.25)

P = 0.5 × (5 + 4)

P = 0.5 × 9

P = 4.5 D

Focal length of lens will be -

f = 1/P

f = 1/4.5

f = 0.2222 m

f = 22.22 cm

Therefore, focal length of lens will be 22.22 cm and power will be 4.5 D.

Thanks dear...