Question

Define Power of lens
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Answer 1

Answer:

Question:

Define Power of lens

Answer:

Power of lens is known as the inverse of the focal length of the lens measured in meter(m).

S.I unit of power = Dioptre (D)

Power of lense = 1/ focal length in meter.

The focal length of 1st lense f1 = 40 cm = 0.4 m

The lense used is a convex lens because the focal length is a positive value.

Power of lense = 1/ focal length

P1 = 1/f1

P1 = 1/0.4

P1 = 2.5 D

The focal length of 2nd lense f2 = -20 cm = – 0.2 m

The lense used is a concave lens because the focal length is a negative value.

P2 = 1/f2

P2 = 1/(-0.2)

P2 = -5 D

Explanation:

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Answer 2

◐ The power of a lens is specified as $\bf{P\:=\:\dfrac{1}{f}}$, where f is the focal length.

◐ The S.I. unit of power of a lens is $\bf{m^{-1}}$.

◐ This is also known as diopter.

◐ The focal length (f) of a converging lens is considered positive and that of a diverging lens is considered negative. Thus, the power of a converging lens is positive and that of the diverging lens is negative.