Question

find the power of concave lens of focal length 2 cm.

Answer 1

The power of the concave lens of focal length 2 cm is 1/2.

Power of concave lens:  

A lens with an inwards curving surface is said to be concave. It has a thicker center and a thinner edge. All of the light rays that have been reflected back through a concave lens are always dispersed. So a diverging lens is another name for a concave lens.

The inverse of the lens's focal length is referred to as the lens' power. It has a length in meters. Dioptres are the S.I. unit of power of the lens. It is denoted by the letter "D".

=> P = 1/f    

Where P is the power of the lens and f is the focal length of the lens.  

Calculations:

Given the focal length of the concave lens = 2 cm  

Power of the lens, P = 1/f = 1/2

Therefore,

The power of the concave lens of focal length 2 cm is 1/2.

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Answer 2

The power of a concave lens of focal length 2 cm is 0.5 dioptre

GIVEN:- focal length 2 cm.

TO FIND:- the power of the concave lens

SOLUTION:-

• The power of a lens is interpreted as the ability or the capacity of a lens either to converge or to diverge away from a beam or an incident ray of light towards or away from a point.
• The unit of Power of a concave lens is dioptre and its formula is D = 1/f

According to the question,

For a lens whose focal length is 2 m, the power of that lens will be:

D = 1/f

D = 1/2

D = 0.5

Hence, the power of a concave lens of focal length 2 cm is 0.5 dioptre

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