Question

A transformer has an efficiency of 80%. It is connected to a power input of $5 \,kW$ at $200\, V$ . If the secondary voltage is $250\, V$ , the primary and secondary currents are respectively

• A. 25 A, 20 A
• B. 20 A, 16 A
• C. 25 A, 16 A
• D. 40 A, 25 A

Answer 1

Answer: (C)

25 A, 16 A

Answer 2

$Efficiency=\frac{output\text{ }power}{input\text{ }power}$
Input power $=5000\text{ }$ W,
Input voltage $=200\text{ }V$
$\therefore$ Primary current, ${{I}_{p}}=\frac{5000}{200}=25\,A$
Output power $=5000\times \frac{80}{100}=4000W$
Output voltage $=250\text{ }V$
Secondary current, ${{I}_{s}}=\frac{4000}{250}=16\,A$