Question

A transformer changes 220 V to 22 V. If the currents in the primary and secondary coils are 10 A and 70 A respectively then its efficiency will be:

• A. 100%
• B. 90%
• C. 70%
• D. 80%

Answer 1

Answer: (C)

70%

Efficiency $=\frac{{Power}_{output}}{{Power}_{input}}\ast 100$
$=\frac{V_2\ast I_2}{V_1\ast I_1}\ast 100$
$=\frac{22\ast 70}{220\ast 10}\ast 100$
$=\frac{7}{10}\ast 100=70$