A copper conductor is 50 m long with a cross-sectional area of 2.5 mm². Using ρ = 1.72 × 10⁻⁸ Ωm, what is its resistance?

R = ρL/A = (1.72e-8 × 50) / (2.5e-6) = 8.6e-7 / 2.5e-6 = 0.344 Ω. Watch the unit conversion: 2.5 mm² = 2.5 × 10⁻⁶ m².

Aluminium has a resistivity of 2.83 × 10⁻⁸ Ωm. A 100 m length with 16 mm² CSA has what resistance?

R = ρL/A = (2.83e-8 × 100) / (16e-6) = 2.83e-6 / 16e-6 = 0.177 Ω. Aluminium has roughly 1.6× the resistivity of copper, which is why aluminium conductors need a larger CSA for the same current rating.

What current flows through a 100 m, 1.5 mm² copper conductor (ρ = 1.72 × 10⁻⁸ Ωm) when 12 V is applied across its ends?

R = (1.72e-8 × 100) / (1.5e-6) = 1.147 Ω. I = V/R = 12 / 1.147 = 10.46 A. Note this calculation ignores temperature rise.

Free mock exam

Resistivity & Circuit Calculations — Level 3 Electrical Science Practice

Free topic-focused mock exam: 30 random questions from a pool of 50 on Resistivity & Circuit Calculations, drawn from the wider Level 3 Electrical Science bank. 35-minute timer, 70% to pass, worked explanation on every question. Use this when you've taken the full mock once and want to drill the topics you got wrong.

Questions: 30
Time limit: 35 min
Pass mark: 70% · 21/30
Question bank: 50

Free, no sign-up. Retake as many times as you like — different questions each time.

Sample questions

01A copper conductor is 50 m long with a cross-sectional area of 2.5 mm². Using ρ = 1.72 × 10⁻⁸ Ωm, what is its resistance?
- A0.86 Ω
- B0.172 Ω
- C8.6 Ω
- D0.344 Ω
Why: R = ρL/A = (1.72e-8 × 50) / (2.5e-6) = 8.6e-7 / 2.5e-6 = 0.344 Ω. Watch the unit conversion: 2.5 mm² = 2.5 × 10⁻⁶ m².
02Aluminium has a resistivity of 2.83 × 10⁻⁸ Ωm. A 100 m length with 16 mm² CSA has what resistance?
- A17.7 Ω
- B0.0177 Ω
- C0.177 Ω
- D1.77 Ω
Why: R = ρL/A = (2.83e-8 × 100) / (16e-6) = 2.83e-6 / 16e-6 = 0.177 Ω. Aluminium has roughly 1.6× the resistivity of copper, which is why aluminium conductors need a larger CSA for the same current rating.
03What current flows through a 100 m, 1.5 mm² copper conductor (ρ = 1.72 × 10⁻⁸ Ωm) when 12 V is applied across its ends?
- A52 A
- B5.2 A
- C105 A
- D10.5 A
Why: R = (1.72e-8 × 100) / (1.5e-6) = 1.147 Ω. I = V/R = 12 / 1.147 = 10.46 A. Note this calculation ignores temperature rise.

Common questions

Is the Resistivity & Circuit Calculations mock exam free?

Yes — 100% free, no sign-up needed. Questions are pulled at random from a substantial bank, with a worked explanation on every question after you submit.

Can I retake the mock exam?

Yes. Every attempt picks a different random selection and reshuffles the options, so each retake gives you genuinely new questions. No limit on retakes.

Does this count towards the real qualification?

No — this is independent practice material. To gain the actual qualification you need to sit the official assessment through an approved provider.