Transformers — A/L Physics

What must I remember about Transformers?

• Transformer Principle: Static electrical device transferring AC electrical energy between two isolated circuits via mutual electromagnetic induction at constant frequency.
• Turns and Voltage Ratio (Ideal Transformer): Secondary induced voltage to primary applied voltage ratio equals turns ratio: Vs / Vp = Ns / Np = a; Step-Up (Ns > Np, Vs > Vp); Step-Down (Ns < Np, Vs < Vp).
• Current and Power Relations: For ideal transformer (100% efficiency, Pin = Pout): Vp * Ip = Vs * Is => Is / Ip = Vp / Vs = Np / Ns; stepping up voltage steps down current proportionally.
• Efficiency and Energy Losses: Real efficiency η = (Pout / Pin) * 100% = [Vs Is cos φ / (Vp Ip cos φ)] * 100%; Losses: 1) Copper losses (I²R heating in windings); 2) Iron/Core losses: Eddy currents (reduced by laminating silicon steel core) and Hysteresis loss (reduced by using magnetically soft core of high permeability and low retentivity); 3) Flux leakage.

Test yourself (1 minute)

1. High Voltage AC Power Transmission

   Grid power transmitted at ultra-high voltages (e.g., 132 kV - 400 kV) because high V drastically minimizes transmission current I (I = P/V); Joulean heat dissipation in transmission cables (P_loss = I² R_line = P² R_line / V²) decreases inversely with square of transmission voltage (1/V²).

2. DC Incompatibility

   Transformers operate strictly on alternating current (AC) with time-varying magnetic flux; connecting a DC voltage source produces constant flux (dΦ/dt = 0), inducing ZERO secondary voltage, and burning primary coil due to low DC resistance.

3. Impedance Matching

   A transformer of turns ratio Np/Ns matches load resistance RL to primary source with equivalent input resistance R_in = (Np / Ns)² * RL.

Practise Transformers questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 8: AC & Electromagnetism

What should I study first?

What comes next?

Next in the syllabus

Where does Transformers fit in the syllabus?

Unit 8.6 · Year 2 · Term 1