A thin double convex lens of radii of curvature R_1=20 ~cm and...

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1. AThe focal length of the lens is $f=30 \mathrm{~cm}$ when in air.
2. BThe lens behaves as a concave mirror of focal length $f_M=10 \mathrm{~cm}$ when silvered on the surface of radius $\mathrm{R}_2=60 \mathrm{~cm}$
3. CThe lens behave as a concave lens (diverging lens) if the image space beyond $\mathrm{R}_2=60 \mathrm{~cm}$ radius surface is filled with a transparent liquid of refractive index $\mu=\frac{5}{3}$. The object space prior to the surface of radius $R_1=20 \mathrm{~cm}$ is air.
4. DA beam of rays incident parallel to principal axis focuses at 48 cm behind the lens if water $\left(\mu=\frac{4}{3}\right)$ fills the entire space behind the surface of radius $R_2=60 \mathrm{~cm}$. The object space prior to the surface of radius $R_1=20 \mathrm{~cm}$ is air.