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How are power and focal length of a lens related? You are provided with two lenses of focal length 20 cm and 40 cm respectively. Which lens will you use to obtain more convergent light?

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Answer:

Power of a lens is reciprocal to its focal length. So, smaller focal length means more power. Out of the given lenses, the lens with 20 cm as focal length has more power than the lens with 40 cm as focal length. The lens with higher power should be used to obtain more convergent light.

The lens of focal length 20 cm or power 5.0 D will be used to have more convergent light. This is because lens of small focal length or large power strongly converges the parallel beam of light.

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