An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is 25 D. Focal length of each of the convex lens is

Question

An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is 25 D. Focal length of each of the convex lens is [2024]

Smart Achievers · Accepted Answer

(1)

We know that $P_{e q} = Σ P_{i}$

As given all lenses are identical, 5P = 25 D

$∴ P = 5 D$

$\Rightarrow \frac{1}{f} = 5 \Rightarrow f = \frac{1}{5} m = 20 c m$

Solution

Q.
An effective power of a combination of 5 identical convex lenses which are kept in contact along the principal axis is 25 D. Focal length of each of the convex lens is [2024]

1 20 cm

2 50 cm

3 25 cm

4 500 cm

Ans.
(1)

We know that $P_{e q} = Σ P_{i}$

As given all lenses are identical, 5P = 25 D

$∴ P = 5 D$

$\Rightarrow \frac{1}{f} = 5 \Rightarrow f = \frac{1}{5} m = 20 c m$

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