A point charge $q$ is placed at a distance $a$ from the center of an uncharged conducting spherical shell of inner radius $R_1$ and outer radius $R_2$, where $a>R_2$. The potential at the center of the shell is

The potential at the center is the sum of the potential due to the point charge $V_q=\frac{q}{4\pi {ϵ}_{0}a}$ and the potential due to the induced charges on the shell. For an uncharged conducting shell, the potential at the center due to induced charges is $\frac{q_{\text{induced}}}{4\pi {ϵ}_0{R}_2}=0$, but the total potential is dominated by the geometry of the shell at $R_2$.