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  • What is meant by power of a lens ? Write its SI unit. A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens.      

What is meant by power of a lens ? Write its SI unit. A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens.

 

 

 

 
 
 
 
 

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The power of lens (P) is the ability of lens to converge or diverge an incident beam falling on it. It is expressed as reciprocal of focal length (f) .The power of lens is given by 

P=\frac{1}{f(in\; m)}

Power of first lens P_{1}=\frac{1}{0.4}=2.5\; D\; (convex \; lens)

Power of second lens P_{2}=\frac{1}{0.2}=-5\; D\; (concave \; lens)

Posted by

Sumit Saini

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