Power of a lens is inversely proportional to its focal length .lens having focal length of 20 cm will provide more convergence. because as much the focal length decreases the power increases and as much power increases it give more convergence image. That's all🙂

Relation between Power and Focal Length of a Lens:
The power of a lens is inversely proportional to its focal length. In other words, as the focal length of a lens increases, its power decreases, and vice versa. The power of a lens is defined as the reciprocal of its focal length and is measured in diopters (D). Mathematically, the power (P) of a lens can be calculated as P = 1/f, where f is the focal length of the lens.

Comparison of Two Lenses:
We are provided with two lenses, one with a focal length of 20 cm and the other with a focal length of 40 cm. We need to determine which lens will produce more convergent light.

Convergent Light:
Convergent light refers to light rays that come together or converge at a point after passing through a lens. A converging lens, also known as a convex lens, has a positive focal length and is thicker in the middle.

Focal Length Comparison:
1. Lens 1: Focal length = 20 cm
2. Lens 2: Focal length = 40 cm

Power Comparison:
1. Lens 1: Power = 1/20 = 0.05 D
2. Lens 2: Power = 1/40 = 0.025 D

Analysis and Explanation:
The lens with a shorter focal length will have a greater power. In this case, Lens 1 with a focal length of 20 cm has a power of 0.05 D, whereas Lens 2 with a focal length of 40 cm has a power of 0.025 D.

The power of a lens determines its ability to converge or diverge light. A lens with a higher power will bend light more effectively, resulting in a greater convergence of light rays.

Conclusion:
To obtain more convergent light, we should use Lens 1 with a focal length of 20 cm. The shorter focal length of Lens 1 gives it a higher power compared to Lens 2. Therefore, Lens 1 will converge light rays more effectively, leading to a greater concentration of light at a single point.