Question

Two thin convex lenses of 4d and 6d are placed co-axially at a distance of 20cm apart find the focal length and power of the combination of lenses

Answer 1

puneetbeastAmbitious

Answer 2

Hey dear,

● Answer -
P = 5.2 D
f = 19.23 cm

● Explaination -
# Given-
P1 = 4 D
P2 = 6 D
d = 20 cm = 0.2 m

# Solution -
Equivalent power of combination of lenses is calculated by-
P = P1 + P2 - d.P1P2
P = 4 + 6 - 0.2×4×6
P = 10 - 4.8
P = 5.2 D

Focal length of the combination is -
f = 1 / P
f = 1 / 5.2
f = 0.1923 m
f = 19.23 cm

Therefore, power and focal length of lens combination is 5.2 D and 19.23 cm respectively.

Hope this helps you...