An equiconvex lens of glass$\left({\mu }_g=1.5\right)$ of focal length $10cm$ is silvered on one side. It will behave like a

For equiconvex lens of glass with ${\mu }_g=1.5,\left|R_1\right|=\left|R_2\right|=f=10cm.$                  

Power of silvered lens $P=2P_L+P_M$

$-\frac{1}{F}=2\left(\mu -1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)-\frac{2}{R_2}$

       $=2\left(1.5-1\right)\left(\frac{1}{10}-\frac{1}{-10}\right)-\frac{2}{-10}$

       $=\frac{1}{5}+\frac{1}{5}=\frac{2}{5}$

$F=-2.5cm.$

Therefore, equiconvex lens silvered at one face behaves as a concave mirror of focal length 2.5 cm.