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Question

An eye specialist prescribes spectacles having a combination of a convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this lens combination in Dioptre is:


A
1.5
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B
+1.5
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C
+6.67
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D
6.67
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Solution

The correct option is A 1.5
Focal length of convex mirror, f1=+40 cm
Focal length of concave mirror, f2=25 cm

So, power of combination of lens,

P=P1+P2=1f1+1f2

P=140125=25401000

P=151000

power of combination will be

P=151000×100 m1=1.5 D

Hence, option (a) is correct.

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