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CBSE Class 10 Science Question 17 of 31

Light - Reflection and Refraction — Question 17

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Question 17

A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Answer

Given,

P = +1.5 D

f = ?

We know,

Power of lens (P) = 1focal length\dfrac{1}{\text{focal length}}

As the given power is positive hence, we can say that the lens used is convex (converging) in nature.

Substituting the value of power in formula we get,

+1.5 = 1f\dfrac{1}{\text{f}}

f = 11.5\dfrac{1}{\text{1.5}}

f = 0.67 m

Therefore, focal length is 0.66 m and it is a converging lens.