Question

Two lenses of focalength 25cm and -10cm( convex and concave) respectively are placed in contact find the power of the combination

Answer 1

total focal length=25+(-10)=15cm

power=100/f=100/15=20/3

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Answer 2

hey mates your answer is here

Hey dear,

◆ Answer-

f = +25 cm

◆ Explaination-

# Given-

P1 = + 6 D

P2 = - 2 D

P = ?

f = ?

# Solution-

Let f1, f2 & f be focal length of 1st lens, 2nd lens and combination, and P1, P2 & P be their respective powers.

Power of combination of lenses is calculated by-

P = P1 + P2

P = 6 - 2

P = + 4 D

Focal length of combination is reciprocal of power,

f = 1/P

f = 1/4

f = 0.25 m

f = + 25 cm

Therefore, focal length of the lens combination is +25 cm and it will act as convex lens.

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