Question

two lenses having focal length 40cm and 50cm are join together to form a combined lens find its power​

Answer 1

Explanation:

12th

Physics

Ray Optics and Optical Instruments

Combination of Mirror and Lenses

Two lenses of focal lengths...

PHYSICS

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Asked on December 26, 2019 by

Shubhanjali Thukaram

Two lenses of focal lengths 20 cm and -40 cm are held in contact. The image of an object at infinity will be formed by the combination at

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ANSWER

Equivalent focal length is given by,

f

1

=

f

1

1

+

f

2

1

Here, f

1

=20cm and f

2

=−40cm

∴

f

1

=

20

1

−

40

1

=

40

2−1

⇒f=40cm

∵

ν

1

−

u

1

=

ν

1

−

∞

1

⇒v=f=40cm

∵[u=∞]