Question

A person wears eyeglasses of focal length 80cm .Where is the far point of the person

Answer 1

Answer:

80 cm from the eye

Explanation:

According to lens formula...

1/v - 1/u = 1/f

Here, the person is myopic and hence, a concave lens is used for correction

Thus, f = -80cm and

u = infinity (for calculation of far point)

So, 1/v - 0 = -1/80

Therefore, v = -80

Hope this answer is helpful....

Answer 2

Answer:

The far point of the person is 80cm from the eye.

Explanation:

Given that the focal length of the eyeglasses $f=-80cm$

⇒  The eyeglasses of the person made of concave lens and the person has myopia.

Consider that u = -∞  ⇒ 1/u = 1/-∞ =0

From the mirror formula:    $\frac{1}{f} =\frac{1}{v} +\frac{1}{u}$

                     $\frac{1}{-80}=\frac{1}{v}}$

   ∴               $v=-80cm$

Therefore the person has far point at distance 80cm from his eye.