WASSCE Physics · Paper 1 style

Capacitors

One sample question with the full working. 2 more in the app, with instant feedback and repair sessions for the traps below.

A 2 μF capacitor is charged to 10 V. The charge stored is

A5 μC
B0.2 μC
C20 μC
D12 μC

Show the answer and working

Answer: C

20 μC.

Trap A Capacitor misconceptions: Q = CV; energy = ½CV². Parallel: C = C₁ + C₂. Series: 1/C = 1/C₁ + 1/C₂ (opposite of resistors).

Trap B Inverts a formula: Write the defining equation in words first (density = mass per unit volume), then rearrange algebraically. Check units: kg/m³.

Trap D Adds quantities with different units: Only quantities with the same unit can be added. If the units differ, the formula multiplies or divides them.

Traps in Capacitors

Capacitor misconceptions
Q = CV; energy = ½CV². Parallel: C = C₁ + C₂. Series: 1/C = 1/C₁ + 1/C₂ (opposite of resistors).
Inverts a formula
Write the defining equation in words first (density = mass per unit volume), then rearrange algebraically. Check units: kg/m³.
Adds quantities with different units
Only quantities with the same unit can be added. If the units differ, the formula multiplies or divides them.
Takes part of the condition as the whole answer
Check whether the option is enough on its own. Equilibrium needs zero resultant force AND zero total moment; a complete explanation names every factor in the stem.
Uses the wrong arithmetic operation
Write the formula symbolically and substitute only at the end. Check units: if the units of your answer are wrong, so is the operation.

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