Convergence is inversely proportional to focal length. If the focal length will be more then the degree of convergence will be less and light ray will converge at less.

Introduction:

When it comes to choosing a lens that converges light, we need to consider the focal length of the lens. The focal length determines the degree to which light rays converge or diverge after passing through the lens. In this scenario, we are provided with two lenses with focal lengths of 20 cm and 40 cm respectively. Let's analyze which lens will be more convergent.

Determining the Converging Power:

To determine the converging power of a lens, we look at its focal length. The converging power is inversely proportional to the focal length, meaning a lens with a smaller focal length will have a greater converging power.

Comparing the Lenses:

1. Lens with a focal length of 20 cm:
- This lens has a shorter focal length compared to the other lens, indicating a stronger converging power.
- Light rays passing through this lens will converge at a shorter distance from the lens.
- The shorter focal length allows for a more pronounced bending of light, resulting in a greater convergence.

2. Lens with a focal length of 40 cm:
- This lens has a longer focal length compared to the first lens, indicating a weaker converging power.
- Light rays passing through this lens will converge at a greater distance from the lens.
- The longer focal length causes a less significant bending of light, resulting in a lesser convergence.

Conclusion:

Based on the analysis, the lens with a focal length of 20 cm will have a greater converging power compared to the lens with a focal length of 40 cm. Light passing through the lens with a shorter focal length will converge at a closer distance, indicating stronger convergence. Therefore, if the goal is to converge light more effectively, the lens with a focal length of 20 cm should be used.