Question

how are power and focal length of a lens related,? you are provided with two lenses of focal length 20cm and 40cm . which lens will you use to obtain convergent light.
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Answer 1

Explanation:

power is inversely proportional to focal length

p= 1/f

for 20 cm

p= 1/20 = 0.05

for 40 cm

p= 1/40

= 0.025

so we use lens of focal length 20 cm because it have high converging light

Answer 2

Answer:

P= f/1 ,P∝ f/1

Power of a lens is inversely proportional to its focal length therefore lens having focal length of 20 cm will provide more convergence.