A metallic sphere of radius $R_1$ and charge $+Q$ is nested inside a metallic spherical shell that has radius $R_2$ and charge $–Q$.
Which of the following changes will increase the capacitance of the system?
I: Increase the magnitude of the charge, $Q$.
II: Increase $R_2$ while leaving $R_1$ fixed.
III: Increase $R_1$ while leaving $R_2$ fixed.
IV: Increase both $R_1$ and $R_2$ while leaving the difference in radii, $R_2-R_1$, fixed.