An ideal transformer has

Analyze the question: The question asks which property describes an ideal transformer. An ideal transformer is a theoretical model with no losses at all, so the right answer is the one that describes a loss-free feature.

Concept: An ideal transformer has these characteristics:

• 100% efficiency (power in = power out)
• Zero resistance in the primary and secondary windings (so no copper losses)
• No flux leakage, meaning all the magnetic flux produced by the primary passes through the secondary
• No hysteresis loss (the core material has no energy loss from repeated magnetisation)
• No eddy current loss

Solution, option by option:

• A. Maximum primary resistance: Wrong. An ideal transformer has zero winding resistance, not maximum. High resistance would cause heat loss (I²R, or copper loss).
• B. No flux leakage: Correct. In an ideal transformer, all the flux links both coils perfectly. This is why the voltage ratio equals the turns ratio: Vs/Vp = Ns/Np.
• C. Hysteresis: Wrong. Hysteresis is an energy loss in the core as it is repeatedly magnetised and demagnetised. An ideal transformer has none.
• D. Eddy current: Wrong. Eddy currents are circulating currents induced in the core that waste energy as heat. An ideal transformer has none. (Real transformers reduce them by using laminated cores.)

Exam tip: In "ideal transformer" questions, pick the option that describes the absence of a loss. Remember the real-transformer losses as C-H-E-F: Copper loss, Hysteresis, Eddy current, Flux leakage. An ideal transformer has none of them. Here, "no flux leakage" is the only option stating a loss-free property.