Question

A doctor prescribed corrective lens of power +1.5 D. What is its focal length? *

(a)66cm

(b)6.6cm

(c)660cm

(d)6cm

(c)​

Answer 1

The lens considered in the question is converging lens which is the convex lens. As the distances given in the question are large, so we choose a new scale where, 1 cm represents 5 cm. Focal length, f = 2 cm.

Answer 2

✿ AnSwer :

• Focal length is + 0.67 cm

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✒ GiVen :

• Power of lens (P) = +1.5 D.

✒ To Find :

• Focal length of the lens = ?

✒ SoluTion :

By using the formula,

$\implies$ f = 1/P

$\implies$ f = 1/1.5

$\implies$ f = 10/15

$\implies$ f = + 0.67 cm

Therefore, focal length of the lens is + 0.67cm.

As 0.67 is not included in any option their may be mistake in the options!!

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