Question

If D is the distance of far point for myopic eye than what is the focal length of concave lens required to rectify the defect

Answer 1

It has given that, D is the distance of far point for myopic eye.

We have to find the focal length of concave lens required to rectify the defect.

Solution : first understand what is myopia ?

Myopia is an eye disorder in which you can see clearly objects near to you but object located farther way looks blurry. It is also known as short sightedness or Near sightedness. It can be rectify using concave lens of appropriate focus.

The person suffering of myopia should use concave lens in such a way that image of object placed at infinity is located at distance D.

so, u = ∞ , v = -D

Now, 1/v - 1/u = 1/f

⇒1/-D - 1/∞ = 1/f

⇒f = -D

Therefore focal length of concave lens is -D

Answer 2

GivEn :-

• 'D' is the distance of far point fir myopic eye

To FinD :-

• The focal length of concave lens to rectify the defect of the Vision .

SoluTioN :-

Let us understand the Basic understanding of Myopic Vision .

→ Mypia is an eye disorder in which a person can see the nearly objects and feels difficulty in seeing far way objects . This disorder is also known as shortsightedness or Near sightedness

→ This can be corrected by the use of concave lens in a particular way that the image of object placed at ∞ is located at a distance D

• u = ∞ and v = D

• 1/u - 1/v = 1/f

• 1/∞ - 1/ D = 1/f

• f = - D

$\boxed{ \bf{ \red{★Hence \: focal- length = - D}{} }{} }{}$