Question

The eye of a far sighted person has a near point of 90cm objects nearer than 90cm cannot be seen clearly a converging lens is used to correct the vision of a book placed 25cm find the focal length of the lens

Answer 1

HEYA GM ❤

SEE....THE ATTACHED FILE.....

TQ ❤ ❤

Answer 2

The Focal length of the lens is -34.61cm.

Given:-

Image distance (v) = -90cm

Object distance (u) = -25cm

To Find:-

The Focal length of the lens.

Solution:-

We can easily calculate the Focal length of the lens, simply by using the following procedure.

As

Image distance (v) = -90cm

Object distance (u) = -25cm

Focal length (f) = ?

According to the Lens formula,

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\frac{1}{f} = \frac{u - v}{vu}$

$f = \frac{vu}{u - v}$

$f = \frac{ - 25 \times ( - 90)}{( - 90) - ( - 25)}$

$f = \frac{ 25 \times 90}{ - 90 + 25}$

$f = \frac{2250}{65}$

f = -34.61cm

Hence, The Focal length of the lens is -34.61cm.

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