iGCSE Physics (0625) 4.5.6 The Transformer-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Since the voltage decreases from $240\text{ V}$ to $20\text{ V}$, it is a step-down transformer.
Using the transformer equation: $\frac{V_{p}}{V_{s}} = \frac{N_{p}}{N_{s}}$, where $V_{p} = 240\text{ V}$, $V_{s} = 20\text{ V}$, and $N_{s} = 600$.
Rearranging for the primary turns: $N_{p} = N_{s} \times \left(\frac{V_{p}}{V_{s}}\right) = 600 \times \left(\frac{240}{20}\right)$.
Calculation: $N_{p} = 600 \times 12 = 7200$ turns.
Thus, the transformer is a step-down type with $7200$ turns on the primary coil, matching Option B.
▶️ Answer/Explanation
Detailed solution:
An efficient transformer requires high electrical conductivity in the coils and high magnetic permeability in the core.
Copper is used for the coils because it has very low electrical resistance, minimizing energy loss as heat ($P = I^{2}R$).
The core must be made of a soft magnetic material, such as iron, to easily concentrate and link the magnetic flux between the primary and secondary coils.
Copper is non-magnetic and cannot serve as a transformer core, while iron wires would have too much resistance compared to copper.
Thus, the standard construction uses insulated copper wire coils wound around a soft-iron core.
This ensures maximum efficiency during the voltage transformation process described by $\frac{V_{p}}{V_{s}} = \frac{N_{p}}{N_{s}}$.
Question
The diagram shows a transformer connected to a 240 V a.c. supply.
What is the potential difference across the secondary coil of the transformer?
A 30 V
B 120 V
C 240 V
D 480 V
Answer/Explanation
Ans: B