Q31Written answer
A doctor has prescribed a corrective lens of power \[+\mathbf{1}.\mathbf{5}\text{ }\mathbf{D}\]. Find the focal length of the lens. Is the prescribed lens diverging or converging?
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Worked solution
Ans: It is given that,
Power of a lens,$P=+1.5D$
Focal length of a lens, $f=?$
Power of a lens,$P=\frac{1}{f(metres)}$
$\Rightarrow 1.5=\frac{1}{f}$
$\Rightarrow f=\frac{1}{1.5}=0.66m$
Positive $f$ indicates a convex lens.
Therefore, the focal length of lens is $f=0.66m$ and the lens prescribed is a diverging lens.