Question

A transformer has turns ratio, $\frac{N_s}{N_p}=4$. If a $200\text{V}AC$ voltage is applied across its primary coil, and it carries $1\text{A}$ current, find current in the circuit connected to the secondary coil if the transformer is $80\%$ efficient.

• A. $0.2\text{A}$
• B. $0.4\text{A}$
• C. $0.8\text{A}$
• D. $2\text{A}$

Answer 1

The correct option is A $0.2\text{A}$

Given that the primary current $I_p=1\text{A}$ and

The voltage in primary coil, $E_p=200\text{V}$

By the transformer equation,

$\frac{E_p}{E_s}=\frac{N_p}{N_s}$

$\Rightarrow E_s=\frac{N_s}{N_p}\times E_p=4\times 200=800\text{V}$

The efficiency of a transformer is given by,

$\eta =\frac{P_s}{P_p}=\frac{E_s{I}_s}{E_p{I}_p}$

$\Rightarrow \frac{80}{100}=\frac{800\times I_s}{200\times 1}$

$\Rightarrow I_s=\frac{1}{5}=0.2\text{A}$

Hence, option $\left(A\right)$ is correct.