Question

Lens of focal length 40 cm and another of –20 cm. Write the nature and

power of each lens.​

Answer 1

Explanation:

Power of 1st lens=100/40=+2.5D Convex

Power of 2nd lens=100/-20=-5D Concave

Therefore,

Net power=2.5-5= -2.5D Concave

Answer 2

Answer:

Positive the focal length positive the power

The lens used is convex lens

Power=1/focal length(in metres)

Power=1/0.4=2.5Dioptres

Negative the focal lenth negative the power

Lens used is concave lens

Power=1/f

Power= -1/0.2= - 5Dioptres

Hope this helps you

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