# A diverging lens has a focal length of 4 cm. Its power is______.

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A diverging lens has a focal length of 4 cm. Its power is______.
1. +25 D
2. -25D
3. -0.25D
4. +0.25 D

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Correct Answer - Option 2 : -25D

CONCEPT:​

• Power of Lens: The inverse of the focal length is known as the power of the lens.
• It shows the bending strength for the light ray of the lens.

$P = \frac{1}{f}$

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

• The unit of power of a lens is Dioptre when the focal length of the lens is taken in meter (m).
• The focal length of the convex lens (converging) is positive and that of the concave lens (diverging) is negative.

CALCULATION:

Given that lens is diverging. so focal length is negative.

f = -4 cm = -0.04 m

Power of lens $P = \frac{1}{f} =\frac{1}{-0.04} = -25 D$

P = -25 D

So the correct answer is option 2.