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प्रश्न
A converging lens has a focal length 40 cm. Calculate its power.
संख्यात्मक
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उत्तर
Focal length of the converging lens (f) = +40 cm [f for convex lens is +ive]
\[ \text{Applying, } \mathrm{P} = \frac{100}{f \text{(in cm)}} \]
\[ \Rightarrow \mathrm{P} = \frac{100}{40} \]
\[ \Rightarrow \mathrm{P} = + \ 2.5 \ \text{D} \]
Thus, power is +2.5 D. The positive sign shows that lens is convex.
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