Question

1. A concave lens produces an image 20cm from the lens of an object

placed 30cm from the lens. Calculate the power of the lens.
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Answer 1

Answer:From the mirror equation,

1/f=1/u+1/v

1/f=1/20+1/30

1/f=1/10(1/2+1/3)

1/f=1/10(5/6)

1/f=1/12

f=12cm

Now power=100/12

P=8.3D

But it is concave,

So, p=-8.3D

Explanation: