[" If planc surface of a plano convex lens is silvered,then "],[" it will behave as a "]

The plane surface of a plano-convex lens of focal length f is silvered. It will behave as

The plane surface of a plano-convex lens of focal length f is silvered. It will behave as

What is Plano-convex lens ?

When the plane surface of a plano-convex lens of refractive index 1.5 is silvered, it behaves like a concave mirror with.f = 30 cm. When its convex surface is silvered, it will behave like a concave mirror of focal length