A thin double convex lens of radii of curvature R₁=20 ~cm and R₂=60 ~cm is made-up of a transparent material of refractive index =1.5 . Choose the correct option(s)

Options

1. AThe focal length of the lens is f=30 ~cm when in air.
2. BThe lens behaves as a concave mirror of focal length f_M=10 ~cm when silvered on the surface of radius R ₂=60
3. CThe lens behave as a concave lens (diverging lens) if the image space beyond R ₂=60 ~cm radius surface is fill
4. DA beam of rays incident parallel to principal axis focuses at 48 cm behind the lens if water ( = 4 3 ) fills t