A capacitor of capacitance 2 × 10⁻⁶ F has a potential difference of 200 V. How much charge is stored?

Correct answer: b 4 × 10⁻⁴ C

From V = Q/C, Q = CV = 2 × 10⁻⁶ × 200 = 4 × 10⁻⁴ C.

Why the other options are wrong

• a 1 × 10⁻⁴ C: 1 × 10⁻⁴ C does not come out. Q = CV = 2 × 10⁻⁶ × 200 = 4 × 10⁻⁴ C.
• c 4 × 10⁻³ C: The power of ten is one step too high: 2 × 10⁻⁶ × 200 = 4 × 10⁻⁴, not 4 × 10⁻³.
• d 1 × 10⁻² C: This is far too large: a 2 × 10⁻⁶ F capacitor at 200 V holds 4 × 10⁻⁴ C.