Question

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

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Solution

Step 1: Given dataThe power of the corrective lens prescribed to the patient by the doctor is $P=+1.5D$.Step 2: Formula used$f=\frac{1}{P}\left[wheref=focallength,P=power\right]$Step 3: Calculating the focal lengthSubstituting the value of P in the formula$f=\frac{1}{P}\phantom{\rule{0ex}{0ex}}f=\frac{1}{+1.5}\phantom{\rule{0ex}{0ex}}f=0.67m$The focal length of the lens is 0.67m.The focal length of the corrective lens is positive. The focal length of the converging lens is positive. So The prescribed corrective lens by the doctor is a converging lens.Hence, the focal length of the corrective lens prescribed by the doctor to the patient is $+0.67m$ . The prescribed corrective lens by the doctor is a converging lens.

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