Question

A transformer is used to light $100W-110V$ lamp from $220V$ mains. If the main current is $0.5A$, the efficiency of the transformer is

• A. $90$%
• B. $95$%
• C. $96$%
• D. $99$%

Answer 1

The correct option is A $90$%

Voltage in primary coil $V_p=220$ V

Current in primary coil $I_p=0.5$ A

Thus input power $P_{in}=V_p{I}_p$

Output power (in secondary coil ) $P_{out}=100$ W

$\therefore$ Efficiency of transformer $\eta =\frac{P_{out}}{P_{in}}\times 100$

$⟹$ $\eta =\frac{100}{\left(220\right)\left(0.5\right)}\times 100=90$ %.