First slide

Ray optics

Question

If a person can sees clearly at a distance of 100 cm, then find the power of lens used to see object at 40 cm,

Easy

A

1.0 D
B

2.0 D
C

1.5 D
D

2.5 D

Solution

Here u = 40, v = -100
$\frac{1}{40} - \frac{1}{100} = \frac{1}{f}$
$\frac{5 - 2}{100} = \frac{1}{f}$
$f = \frac{200}{3} cm$
P $= \frac{3}{200} \times 100 = \frac{3}{2} = 1.5 D$

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