Question

A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be :

• A. $8A$
• B. $4A$
• C. $5A$
• D. $9A$

Answer 1

The correct option is B $4A$

We know that$\frac{N_s}{N_p}=\frac{V_s}{V_p}\Rightarrow \frac{1}{20}=\frac{V_s}{2400}\Rightarrow V_s=120V$

Now, for $100\%$ efficiency

$V_{sis}=V_{pip}\Rightarrow 120\times 80=2400\left(ip\right)\therefore ip=\frac{120\times 80A}{2400}ip=4A$