Question

6.<br />A convex lens has a focal length of 0.5 m. It has to be combined with a second lens, so that the combination<br />has a power of 1.5 dioptre. Which of the following could be the second lens?​

Answer 1

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Explanation:

12th

Physics

Ray Optics and Optical Instruments

Combination of Lenses

A convex lens has a focal l...

PHYSICS

A convex lens has a focal length of 0.5m. It has to be combined with a second lens, so that the combination has a power of 1.5 dioptre. Which of the following could be the second lens?

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ANSWER

Power of combination P=1.5 dioptre

Power of convex lens having focal length of 0.5m, P

1

=

0.5

1

dioptre

Using P=P

1

+P

2

∴ 1.5=

0.5

1

+P

2

We get P

2

=−0.5 dioptre

Thus focal length of second lens f

2

=

P

2

1

⟹ f

2

=−

0.5

1

=−2m (negative sign implies the lens must be a concave lens)

Thus second lens could be concave lens of focal length 2m.