VCE Physics — Unit 3 AOS 2
Transformers — Flashcards & Quiz
Transformers use electromagnetic induction to change AC voltages up or down, and VCE Physics Unit 3 AOS 2 expects you to apply the ideal turns ratio, explain why transformers only work with AC, and justify why long-distance power transmission uses high voltages and low currents.
Key Points
- Turns ratio: V_s/V_p = N_s/N_p. Step-up has N_s > N_p; step-down has N_s < N_p.
- Ideal transformer: input power equals output power, so V_p I_p = V_s I_s. Stepping voltage up requires stepping current down.
- Only AC works — DC produces constant flux (dΦ/dt = 0) and therefore no induced EMF in the secondary.
- Real losses: resistance in the coils (I²R heating), eddy currents (reduced by lamination), hysteresis, and flux leakage.
- Power transmission uses step-up at the source and step-down near consumers. Lower I for the same P reduces I²R losses in the transmission lines.
- Efficiency η = P_out/P_in is typically >95% for modern transformers operating near rated load.
Common Mistakes to Avoid
- Claiming transformers work on DC — they need changing flux.
- Forgetting the inverse current-voltage relationship when power is conserved.
- Mixing up step-up (more secondary turns) and step-down (fewer secondary turns).
- Ignoring real losses in efficiency calculations.
- Applying the ideal transformer equation V_s/V_p = N_s/N_p in reverse without justification.
Exam Strategy
VCAA Unit 3 AOS 2 transformer questions give turns ratios or voltage/current values and ask you to calculate the unknown. Method: (1) write the turns ratio and power-conservation equations, (2) substitute known values, (3) for power transmission questions, link to I²R losses and explain the high-voltage choice, (4) account for real losses if efficiency is given.
Revision Tip
Transformer calculations are procedural — drill a Revizi deck with step-up and step-down scenarios covering both directions of the calculation.
Related Concepts
Last updated: March 2026