The correct relation between the focal length of a lens and its power is:

Correct option is A

The correct answer is:(A) P = 1/f

The power of a lens (P) is related to the focal length (f) by the formula:$$P = \frac{1}{f}$$​​

Where:

• P is the power of the lens in diopters (D),
• f is the focal length of the lens in meters (m).

This formula is correct and applies universally to both convex (converging) and concave (diverging) lenses.

The power of a lens is the inverse of its focal length. The sign of the power will depend on whether the lens is converging or diverging:

• For convex lenses, the focal length is positive, and the power is positive.
• For concave lenses, the focal length is negative, and the power is negative.

Information booster:

 P = −1/f: This formula is not universally correct. The formula for the power of a lens is P=1/f P=1fP = \frac{1}{f}
​, and the negative sign applies only to concave (diverging) lenses, not as a general rule.

P ∝ f: This is incorrect. The power is inversely proportional to the focal length, not directly proportional. As the focal length increases, the power decreases.

 P = f: This is incorrect because it does not represent the correct relationship between power and focal length.

Key Points:

• ​$$P = \frac{1}{f}$$​The power of a lens is given by
• The sign of the power depends on the type of lens: positive for converging lenses and negative for diverging lenses.