Question

A transformer having efficiency of $90$% is working on $200V$ and $3kW$ power supply. If the current in the secondary coil is $6A$, the voltage across the secondary coil and the current in the primary coil respectively are

• A. $300V,15A$
• B. $450V,15A$
• C. $450V,13.5A$
• D. $600V,15A$

Answer 1

The correct option is B $450V,15A$

Given that,

Efficiency of the transformer

$n=90\%$

Input Power, $P_{in}=3kw=3000w$

voltage across the primary coil,

$v_P=200v$.

Current in the secondary coil, $1s=6A$

As $P_{in}=I_P{V}_P$

$\therefore$ Current in the primary coil,

$I_P=\frac{P_{in}}{V_P}=\frac{3000w}{200v}=15A$

Efficiency of the transformer,

$n=\frac{P_{out}}{P_{in}}=\frac{V_s{I}_s}{V_P{I}_p}$

$\therefore \frac{90}{100}=\frac{6v_S}{3000}$ or $v_s$

$=\frac{90\times 3000}{100\times 6}=450v$

$\therefore [450v,15A]$