Question

How does the power of a lens change if its focal length decreases to half? What is the unit of power of lens?

2 points


How does the power of a lens change if its focal length decreases to half? What is the unit of power of lens?


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Answer 1

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How does the power of a lens change if its focal length decreases to half? What is the unit of power of lens?

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How does the power of a lens change if its focal length decreases to half?

• ❭ P= f/1
• ❭ Thus, when f becomes 2f, P'=1/2f =P/2
• ❭ i.e. power is halved.

What is the unit of power of lens?

• ❭ Dioptre is the unit of power of lens.

Answer 2

Answer:

Question

How does the power of a lens change if its focal length decreases to half? What is the unit of power of lens?

Solution

The degree of convergence and divergence of light rays achieved by a lens is expressed in terms of power.

$\boxed{p = \frac{1}{f} }$

where

p= power of lens

f= focal lenght

▪️Power of lens is inversely proportional to Focal length.

・if Focal length is decreased to half the power will get doubled

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$\bold{・S.I \: unit \: of \: Power \: of \: lens \: is \: \green {dioptre }\: denoted \: by \: \red{ "D".}}$

✿ 1 dioptre is the power of lens whose focal length is 1 metre

• power of convex lens is +ve
• power of concave lens - ve

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