The power of a concave lens of focal length 25" " cm is _________.

Correct option is C

Sol: The correct answer is (c) -4D

Given:

Focal length of the concave lens, $$f$$ = -25 cm(negative because it's a concave lens).

​Formula used:

P = $$\frac{1}{f}$$

Where,

P is the power of the lens in diopters (D),

$$f$$​is the focal length in meters (m).

Solution:

Convert the focal length into meters:

​$$f$$ = -25cm = -0.25m

P = $$\frac{1}{f}$$

P = $$\frac{1}{-0.25}$$

P = -4D