Final answer:
The capacitance of the cylindrical capacitor is 25 pF. To find the ratio of their radii, additional information or a more detailed examination of the problem context would be required, as the ratio depends on the specific dimensions and constants of the cylindrical capacitor.
Step-by-step explanation:
When solving for the capacitance of a cylindrical capacitor, we can use the formula C = Q/V, where C is the capacitance, Q is the charge, and V is the potential difference. Given the charge of 0.500 nC (nanoCoulombs) and a potential difference of 20.0 V (Volts), the capacitance is calculated as follows:
C = Q/V = 0.500×10-9 C / 20.0 V = 25×10-12 F
The capacitance of the system is 25 pF (picoFarads).
To find the ratio of the radii of the cylinders, since the length l is given as 1.0 m and other constants are known, we would typically apply the formula for the capacitance of a cylindrical capacitor involving the radii and the length, but since those specific values are not provided here, the formula cannot be applied directly without additional information.