Capacitance of an isolated conducting sphere of radius \( R_1 \) becomes \( n \) times when it is enclosed by a concentric conducting sphere of radius \( R_2 \) connected to earth. The ratio of their radii \( \left( \dfrac{R_2}{R_1} \right) \) is:
\( \dfrac{n}{n-1} \)
\( \dfrac{2n}{2n+1} \)
\( \dfrac{n+1}{n} \)
\( \dfrac{2n+1}{n} \)
