A 100 μF capacitor is charged to 9 V. What is the energy stored?

A 100 μF capacitor is charged to 9 V. What is the energy stored?

• A. 0.81 mJ
• B. 4.05 mJ
• C. 0.405 J
• D. 0.0405 J

Answer: (B)

Energy stored in a charged capacitor is given by E = 1/2 C V^2. Convert 100 μF to farads: 100 μF = 100 × 10^-6 F = 1.0 × 10^-4 F. With V = 9 V, E = 0.5 × (1.0 × 10^-4 F) × (9^2) = 0.5 × 1.0 × 10^-4 × 81 = 4.05 × 10^-3 J, which is 0.00405 J or 4.05 mJ. So the energy stored is 4.05 millijoules. This matches the given value because all steps follow the standard capacitor energy formula and proper unit conversion.

Energy stored in a charged capacitor is given by E = 1/2 C V^2. Convert 100 μF to farads: 100 μF = 100 × 10^-6 F = 1.0 × 10^-4 F. With V = 9 V, E = 0.5 × (1.0 × 10^-4 F) × (9^2) = 0.5 × 1.0 × 10^-4 × 81 = 4.05 × 10^-3 J, which is 0.00405 J or 4.05 mJ. So the energy stored is 4.05 millijoules. This matches the given value because all steps follow the standard capacitor energy formula and proper unit conversion.