Question

find the focal length and nature of lens which should be placed in contact with a lens of focal length 10cm so that the power of the combination becomes 5 diopter (minus 20 cm and concave) give the ans. in image

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Answer 1

Answer:

Explanation:

Power(P2) of lens with 10 cm focal length = 10010=10D

Let Power of the lens is P1

Total power of combination = P1 +P2

​5D=​ P1 + 10D

P1 = -5D

focal length = −15=−0.2m⇒−20 cm

Power of the lens is negative so the given lens is concave lens