Question

A person cannot see distinctly any object placed beyond 40cm from his eyes. Calculate the
power of the lens which will help him to see distant objects clearly.
a. -2.5 Dioptre
b.-1.5 Dioptre c. +2 Dioptre
d. +1 Dioptre​

Answer 1

Answer:

a)-2.5 dioptre

Explanation:

Answer 2

Answer:

-2.5 dioptre

Explanation:

A lens which can bring an object at infinity to 40 cm is required here.

Here, u = -∞ and v = -40 cm

 

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

We get, 1/f = (1/-40) - (1/-∞) = - 1/40

or, f = -40 cm

 

Power = 100 /  f in cm = 100/(-40) = -2.5 dioptre