Question

Two convex lenses of equal focal lengths are kept in contact with each other. If the power of their combination is 20D, find the focal length of each convex lens.​

Answer 1

Hope this will help you...

Answer 2

The focal length of each convex lens is 0.1 m or 10 cm.

Given:

Power of the combined lens = 20 D

To find:

Focal length of each convex lens = ?

Formula to be used:

• $\frac{1}{f}=\frac{1}{f_1} +\frac{1}{f_2}$
• $P = \frac{1}{f}$

Calculation:

$\frac{1}{f}=\frac{1}{f_1} +\frac{1}{f_2}$

$\frac{1}{f}=\frac{1}{f_1} +\frac{1}{f_1}$

$\frac{1}{f}=\frac{2}{f_1}$  .......... (1)

As $P = \frac{1}{f}$, substituting it in the (1), it gives

P = $\frac{2}{f_1}$

20 = $\frac{2}{f_1}$

$\frac{20}{2} =f_1$

10 = $f_1$

Conclusion:

From the above calculation, it is inferred that the focal length of convex lens is calculated as 10 cm.

Learn more about such concept

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