Question

The power of lens is +2.5D, what kind of lens it is? what is its focal length?
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Answer 1

power = 1/f

2.5=1/f

f=1/2.5

f=10/25=2/5=0.4m

lens is convex

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Answer 2

Solution:-

we know that power P=2.5D

$p = \frac{1}{f} \\ f = \frac{1}{2.5} = 0.4cm \: = 40cm$

Since the focal length of lens is positive so it is a convex lens. It is a converging lens.