Question

10. Which of the following is a true statement?
O 1. The power of a lens is always positive.
O 2. The power of a lens is always negative.
O 3. The power of a convex lens is positive.
04. The power of a concave lens is positive.​

Answer 1

4) The power of a concave lens is positive.

Answer 2

To find:

Which of the following is a true statement?

• The power of a lens is always positive.
• The power of a lens is always negative.
• The power of a convex lens is positive.
• The power of a concave lens is positive.

Solution:

• Power of any lens represents its capability to converge or diverge the incident electromagnetic rays (e.g. light rays).

• So, higher the power , higher will be the converging/diverging capability.

• Mathematically , power can be calculated as the reciprocal of the the focal length of the lens.

For a convex lens , focal length is positive.

$\rm{ \therefore \: power = \dfrac{1}{focal \: length} }$

$\rm{ = > \: power = \dfrac{1}{ + f} }$

$\rm{ = > \: power = + ve}$

So, power of convex lens is positive.

Other options are eliminated because:

• Power of lens can be both positive and negative.

• Power of a concave lens is always negative.

Hope It Helps.