Question

A step down transformer is used to reduce the main supply of $220\text{V}$ to $10\text{V}$. If the primary draws $5\text{A}$ and secondary draws $88\text{A}$ current, calculate the efficiency of the transformer.

• A. $60$%
• B. $70$%
• C. $80$%
• D. $90$%

Answer 1

The correct option is C $80$%

$e_p=220\text{V},e_s=10\text{V},I_p=5\text{A}$ and $I_s=88\text{A}$
Input power $\left(P_i\right)=e_p\times I_p=220\times 5=1100\text{W}$
Output power $\left(P_o\right)=e_s\times I_s=10\times 88=880\text{W}$
Efficiency $\eta =\frac{P_o}{P_i}=\frac{880}{1100}=0.8$ or $80\%$