If focal length of human eye is 2 cm, then find the focal length of contact lens, such that a combined focus system of focal length 2.5 cm is obtained after using contact lens.

Question

If focal length of human eye is 2 cm, then find the focal length of contact lens, such that a combined focus system of focal length 2.5 cm is obtained after using contact lens. (A) -1 cm (B) -5 cm (C) -10 cm (D) -20 cm

Tardigrade Admin · Accepted Answer

Pnet = Peye + Plens (1/fnet)=(1/feye)+(1/flens) (1/2.5)=(1/2)+(1/flens) or flens=-10 cm

Q. If focal length of human eye is $2 c m$ , then find the focal length of contact lens, such that a combined focus system of focal length $2.5 c m$ is obtained after using contact lens.

-1 cm

-5 cm

-10 cm

-20 cm

P_net = P_eye + P_lens
$\frac{1}{f _{n e t}} = \frac{1}{f _{eye}} + \frac{1}{f _{l e n s}}$
$\frac{1}{2.5} = \frac{1}{2} + \frac{1}{f _{l e n s}}$ or $f_{l e n s} = - 10$ cm

Q. If focal length of human eye is 2cm, then find the focal length of contact lens, such that a combined focus system of focal length 2.5cm is obtained after using contact lens.