When `n_1 lt n_2`, light goes from rarer to denser medium. Therefore, on passing through a convex lens, it converges,
(ii) When `n_1=n_2`, there is no change in medium.Therefore, no bending or refraction occurs as shown in figure.
(iii) When `n_1 gt n_2`, light goes from denser to rarer medium. Therefore, no passing through a convex lens, it diverges as shown in figure.