Question

A transformer with efficiency 80% works at $4\, kW$ and $100\, V$. If the secondary voltage is $200\,V$, then the primary and secondary currents are respectively

• A. 40 A and 16 A
• B. 16 A and 40 A
• C. 20 A and 40 A
• D. 40 A and 20 A

Answer 1

Answer: (A)

40 A and 16 A

Answer 2

Here, $\eta$ = 80 % $P_{i}$ = 4 kW = 4000 W $V_{p}$ = 100 V, Vs = 200 V $I_{p}=\frac{p_{i}}{V_{p}}=\frac{4000}{100}=40\,A$ $\eta=\frac{V_{s}\,I_{s}}{V_{p}\,I_{p}};\, \frac{80}{100}=\frac{200I_{s}}{4000}=\frac{I_{s}}{20}$ or $I_{s}=\frac{20\times80}{100}=16\,A$