Question

A man after using a spectacles can read a book kept at a distance of 25 cm. The power of lens, used, is -2.0 D.
Without spectacles upto what distance a person can read the book?​

Answer 1

Answer:

1) It is a defect of eye it is myopia

2) myopia means a they cannot see near objects he can see for object

3) They can see up to certain point that called for point behind the for point they can see the book

Answer 2

The person can read the book up to  50 cm without spectacles.

Explanation:

The power of the lens, P = -2 D.

The focal length,

  $f=\frac{1}{P} =\frac{1}{-2D}$

$f=-0.5m$

Given image distance, v = -25 cm =- 0.25 m

Use lens formula,

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

substitute the value, we get

$\frac{1}{-0.5m} =\frac{1}{-0.25m} -\frac{1}{u}$

$\frac{1}{0.5m} -\frac{1}{0.25m}=\frac{1}{u}$

$\frac{1}{u}=2m-4m$

u = -0.50 m = -50 cm

Thus, the person can read the book up to  50 cm without spectacles.

#Learn More: lens formula

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