Which one of the following spherical lenses do not exhibit dispersion?
1) Convex lens with radius of curvature 10 cm and 20 cm
2) Concave lens with radius of curvature 10 cm and 20 cm
3) Convex lens with radius of curvature 10 cm and 10 cm
4) Concave lens with radius of curvature 20 cm and 20 cm