Question

Two thin lenses of power +5D and -2D are placed in contact with each other. What is the focal length of the combination

Answer 1

Answer:

The focal lenght of the mirror is 0.33 m

Explanation:

First we find the combination power of both the lenses

power of combination= P1 + P2

                                    = 5 - 2

                                    = 3D

now, focal lenght = 1/P

                             = 1/3

                             = 0.33 m

Answer 2

The focal length of the combination is 33.33 cm.

Explanation:

Given that,

Power of one lens = +5D

Power of other lens = -2D

We need to calculate the power of combination

Using formula combination

$P=P_{1}+P_{2}$

Put the value into the formula

$P=5-2=3\ D$

We need to calculate the focal length of the combination

Using formula of focal length

$f=\dfrac{1}{P}$

Put the value into the formula

$f=\dfrac{100}{3}$

$f=33.33\ cm$

Hence, The focal length of the combination is 33.33 cm.

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Topic : Power

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