WASSCE Physics · Paper 1 style

Electricity

One sample question with the full working. 9 more in the app, with instant feedback and repair sessions for the traps below.

Two capacitors of 2 μF and 3 μF are connected in parallel. The effective capacitance is

A5 μF
B0.83 μF
C6 μF
D1.2 μF

Show the answer and working

Answer: A

In parallel, C = C₁ + C₂.

Trap B Forgets to invert the reciprocal at the end: With 1/R = 1/R₁ + 1/R₂ (or 1/v), the sum gives 1/R. Finish with R = 1 ÷ (sum). Check: parallel R must be smaller than the smallest resistor.

Trap C 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.

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

Traps in Electricity

Forgets to invert the reciprocal at the end
With 1/R = 1/R₁ + 1/R₂ (or 1/v), the sum gives 1/R. Finish with R = 1 ÷ (sum). Check: parallel R must be smaller than the smallest resistor.
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.
Capacitor misconceptions
Q = CV; energy = ½CV². Parallel: C = C₁ + C₂. Series: 1/C = 1/C₁ + 1/C₂ (opposite of resistors).
Rearranges a formula wrongly
Use the triangle or do the algebra: from V = IR, divide both sides by R → I = V/R. Check with units (V/Ω = A).
Converts only one unit of a compound unit
Convert each unit separately: km → m (× 1000) and h → s (÷ 3600). Together: km h⁻¹ ÷ 3.6 = m s⁻¹.
Leaves a quantity out of the formula
Write the full formula and tick off each symbol as you substitute. Every symbol needs a value.
Reverses a relationship or direction
Write the relationship with an arrow or proportionality sign first (E ∝ f; R ∝ L; cooling a metal → R falls). Then check the option follows the same direction.
Picks a related law, device or effect with a different job
Learn laws and devices as 'name → what it tells you' cards. Contrast neighbours: left-hand rule = motor force, right-hand rule = dynamo current, grip rule = field around a wire.
Mixes up a pair of similar physics terms
Make a two-column table for each pair with one defining feature and an example. Underline the defining word in the stem before you look at the options.
Uses everyday intuition instead of physics
Name the law that applies (Newton's first law, Archimedes' principle, kinetic theory) and reason from it. If the option only 'feels' right, test it against the law.
Over-generalises a rule
Every rule has conditions. Before choosing, ask which waves, which media, which angles or which components the rule really applies to.
Confuses series and parallel combinations
Series: R = R₁ + R₂ (total is larger). Parallel: 1/R = 1/R₁ + 1/R₂ (total is SMALLER than the smallest). Use this to sanity-check.
Writes a quantity in the wrong unit
Carry units through every line. A percentage is a ratio × 100; joules and newtons cannot become % without dividing by a quantity of the same kind.

Practise Electricity (9 questions)Send to your class on WhatsApp