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प्रश्न
An eye specialist prescribes a number +4.5 D to a person for his glasses. What is the nature of the lens? What is the focal length of the lens?
संख्यात्मक
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उत्तर
(i) As the power is +4.5 D, therefore the lens is convex.
(ii) \[ \text{Applying, } \mathrm{P} = \frac{100}{f \text{(in cm)}} \]
\[\Rightarrow \ 4.5 = \frac{100}{f \text{(in cm)}}\]
\[f \text{(in cm)} = \frac{100}{4.5} \ \text{cm}\]
\[\therefore f \text{(in cm)} = + \ 22.22 \ \text{cm} \]
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