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.