Question

The far point of a person is 3 m from the eye. Name the defect of vision he is suffering from. What is the power of the corrective lens?
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Answer 1

Person is suffering from short-sightedness i.e myopia.

Given,

V (far point) = -3m

U = infinite

From lens making formula,

1/f = 1/v -1/u

1/f = 1/-3

f = -3

Now,

Power of lens(concave lens)

P = 1/f

P= 1/-3

P= -0.33D

Answer 2

Concept introduction:

The diopter is a unit of measurement for a lens' refractive power. The reciprocal of a lens' focal length in meters is its power, or $D = 1/f$, where $D$ is the power in diopters and f is the focal length in meters.

Given:

Here it is given that The far point of a person is $3 m$ from the eye.

To find:

We have to find  defect of vision he is suffering from and what is the power of the corrective lens.

Solution:

According to the question,

The defect of vision he is suffering from is called myopia.

$1/f = 1/v -1/u\\= > 1/f = 1/-3\\= > f = -3$

Now, power of lens(concave lens)

$P=1/-3\\= > P=-0.33D$

Final answer:

Hence the final answer of the question is myopia and $-0.33D$.

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