A capacitor with capacitance C = 0.5 μF is charged to voltage V = 6 V. What is the energy stored in the capacitor?

A capacitor with capacitance C = 0.5 μF is charged to voltage V = 6 V. What is the energy stored in the capacitor?

• A. 4.5 μJ
• B. 27 μJ
• C. 18 μJ
• D. 9 μJ

Answer: (D)

The energy stored in a charged capacitor is found from U = (1/2) C V^2. Here C = 0.5 μF, which is 0.5 × 10^-6 F = 5 × 10^-7 F, and V = 6 V, so V^2 = 36. Plugging in: U = (1/2) × (5 × 10^-7) × 36 = (1/2) × 1.8 × 10^-5 = 9 × 10^-6 J, which is 9 μJ. So the capacitor stores 9 microjoules.

The energy stored in a charged capacitor is found from U = (1/2) C V^2. Here C = 0.5 μF, which is 0.5 × 10^-6 F = 5 × 10^-7 F, and V = 6 V, so V^2 = 36. Plugging in: U = (1/2) × (5 × 10^-7) × 36 = (1/2) × 1.8 × 10^-5 = 9 × 10^-6 J, which is 9 μJ. So the capacitor stores 9 microjoules.