Question

The transformer is used to light $100W–110V$lamps 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

$90\%$

Step 1: Given data

Power $P_0=100W$

Voltage $V_0=110V$

Voltage $V_i=220V$

Current $i=0.5A$

Step 2: To find

The efficiency of the transformer $\eta$=?

Step 3: Calculation

$P_i=V_{i}i$

$P_i=220\times 0.5$

$P_i=110W$

The efficiency of the transformer, $\eta =\frac{P_0}{P_i}x100$

$\eta =\frac{100}{110}x100$

$\eta =90.9\%$

So, the efficiency of the transformer is $90\%$.

Hence, the correct option is A.