Introduction:
When light passes through a lens, it refracts or bends. The amount of bending depends on the shape of the lens and the angle at which the light hits it. The degree of bending depends on the curvature of the lens surfaces and the refractive index of the lens material.

Explanation:
The degree of convergence of refracted light depends on the focal length of the lens. The shorter the focal length of the lens, the greater the degree of convergence. Therefore, in this case, the lens with a focal length of 10 cm would provide greater convergence of refracted light as compared to the lens with a focal length of 20 cm.

Explanation with Formula:
The formula for calculating the degree of convergence of refracted light is given as:
1/f = 1/u + 1/v
where f is the focal length of the lens, u is the distance of the object from the lens, and v is the distance of the image from the lens.

For a lens with a shorter focal length, the value of 1/f would be greater than that of a lens with a longer focal length. This implies that the degree of convergence of refracted light would be greater for a lens with a shorter focal length as compared to a lens with a longer focal length.

Conclusion:
Therefore, to obtain greater convergence of refracted light, it is recommended to use a lens with a shorter focal length. In this case, the lens with a focal length of 10 cm would provide greater convergence of refracted light as compared to the lens with a focal length of 20 cm.

I would suggest to use the lens with focal length of 10 cm to obtain greater convergence because the power of convergence or divergence of a lens(D) is inversely equal to the focal length of the lens.