Question

A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact each other. What is the power and focal length of this combination of lenses. ​

Answer 1

Explanation:

total power= P1+P2

5D+ 7.5D= 12.5D

1/total focal length= 1/F1+1/F2

however,

1/F = P

Therefore

1/total focal length= 5+7.5= 12.5

total focal length= 1/12.5 m

0.08m

8cm

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