The far point of a myopic person is 150 cm in front of the eye. Calculate the focal length and the power of lens required to enable him to see the distant objects clearly.

Asked by Topperlearning User | 3rd Jun, 2016, 09:53: AM

Expert Answer:

Far point of the myopic person = 150 cm. For him to be able to clearly see very distant objects, the image should be made at 150 cm in front of the eye.

Using lens formula,

begin mathsize 12px style 1 over straight f equals 1 over straight v minus 1 over straight u
1 over straight f equals fraction numerator 1 over denominator negative 150 end fraction minus 1 over infinity
rightwards arrow straight f equals negative 150 space cm space equals space minus space 1.5 space straight m
Power space of space lens equals 1 over straight f equals fraction numerator 1 over denominator negative 1.5 space straight m end fraction equals negative 0.66 space straight D
end style

Therefore, a concave lens of power -0.66 D has to be used.

Answered by  | 3rd Jun, 2016, 11:53: AM