Paper 2 Transformers Drills

Q1 Ideal Transformer Ratios

An ideal transformer has $N_p=400$ and $N_s=2400$. The primary rms voltage is $12.0\mathrm{V}$ and the secondary supplies $0.30\mathrm{A}$.

1. Calculate secondary rms voltage. [2]
2. Calculate primary rms current. [2]
3. State whether this is a step-up or step-down transformer. [1]

Q2 Transformer Operation

1. Explain why the primary and secondary coils need not be electrically connected. [2]
2. Explain why an alternating supply is needed. [2]
3. State the role of the iron core. [1]

Q3 Efficiency

A real transformer supplies a resistive load. The primary voltage and current are in phase and have rms values $230\mathrm{V}$ and $0.80\mathrm{A}$; the secondary rms values are $12.0\mathrm{V}$ and $13.5\mathrm{A}$.

1. Calculate input power. [1]
2. Calculate output power. [1]
3. Calculate efficiency. [2]