HSC Physics — Module 6
Transformers — Flashcards & Quiz
Transformers convert AC voltages by electromagnetic induction and are central to HSC Physics Module 6: Electromagnetism. You need to apply the turns ratio Vp/Vs = Np/Ns, explain why transformers only work with AC, and account for the main sources of real-world energy loss — resistive heating, eddy currents, hysteresis and flux leakage. Power transmission questions usually link transformers to the I²R loss argument: stepping voltage up reduces current, which reduces resistive loss in transmission lines.
Key Points
- Transformers use electromagnetic induction to step AC voltage up or down. Only AC works — DC produces no changing flux.
- Turns ratio: V_s/V_p = N_s/N_p. Step-up transformer: N_s > N_p; step-down: N_s < N_p.
- Ideal transformer: input power = output power, so V_p × I_p = V_s × I_s. Higher voltage → lower current on the secondary.
- Real losses: resistive heating in coils (I²R), eddy currents (reduced by laminated cores), hysteresis (energy lost re-magnetising), flux leakage.
- Power transmission: grid uses step-up transformers to minimise I²R losses in transmission lines, then step-down transformers near consumers.
- HSC exam skill: derive the turns ratio from Faraday's law assuming 100% flux linkage; then apply energy conservation for the current ratio.
Common Mistakes to Avoid
- Claiming transformers work with DC — they don't. DC gives constant flux and no induced EMF.
- Forgetting the voltage-current inverse relationship — higher V means lower I (power conservation in ideal transformer).
- Confusing step-up (more secondary turns) with step-down (fewer secondary turns).
- Ignoring real-world losses (resistance, eddy currents, hysteresis, flux leakage) when asked about efficiency.
- Applying the ideal transformer equation V_s/V_p = N_s/N_p in reverse without justification.
Exam Strategy
HSC Module 6 transformer questions usually give turn ratios or voltage/current values and ask you to calculate the unknown. Always write the ideal transformer equations first: V_s/V_p = N_s/N_p and V_p × I_p = V_s × I_s. For power transmission questions, link to I²R losses: stepping up voltage reduces current, which reduces heat loss in transmission lines.
Sample Flashcards
Q1: How does a transformer work and what is the transformer equation?
A transformer transfers electrical energy between circuits using electromagnetic induction. AC in the primary coil creates a changing magnetic flux in an iron core, which induces an EMF in the secondary coil. Transformer equation: V_p/V_s = N_p/N_s = I_s/I_p. Step-up: N_s > N_p. Step-down: N_s < N_p.
Q2: Why do transformers only work with AC and not DC?
Transformers require a CHANGING magnetic flux to induce an EMF in the secondary coil (Faraday's law). AC continuously changes direction, creating a continuously changing flux. DC produces a constant flux — no change means no induced EMF (except briefly when DC is first switched on or off).
Sample Quiz Questions
Q1: A transformer can work with both AC and DC input.
Answer: FALSE
Transformers require changing flux (Faraday's law). AC provides continuously changing current/flux. DC produces constant flux — no change means no induced EMF in the secondary. Transformers only work with AC.
Q2: A step-up transformer increases voltage and decreases current.
Answer: TRUE
V_s/V_p = N_s/N_p. A step-up has more secondary turns, so V_s > V_p. By conservation of energy (P = VI): if V increases, I must decrease proportionally. V_pI_p = V_sI_s.
Q3: An ideal transformer has 100% efficiency with no energy losses.
Answer: TRUE
An ideal transformer transfers all energy from primary to secondary: P_p = P_s, so V_pI_p = V_sI_s. Real transformers have losses from resistance, eddy currents, hysteresis, and flux leakage, achieving about 95-99% efficiency.
Revision Tip
Transformer calculations are procedural — drill a Revizi flashcard deck of voltage/current/turn problems for both step-up and step-down configurations.
Related Concepts
Last updated: March 2026 · 2 flashcards · 3 quiz questions