When does a convex lens behave as a concave lens ?

Under what conditions a concave lens can behave as a converging lens?

In what condition a convex lens behave like a concave one? ,

What is the sign of the power of (i) a convex lens (ii) a concave lens ?

If the refractive index of convex lens and surrounding medium be mu_1 and mu_2 respectively then for convex lens to act as concave lens when

Answer the following questions : What is the sign of the power of a convex lens a concave lens ?

State two differences between a convex lens and a concave lens. Give one use of convex lens and one of concave lens.