Q. 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) $1600\ A$
B) $20\ A$
C) $4\ A$
D) $1.5\ A$
Explanation
(c) $\frac{N_{s}}{N_{p}} = \frac{V_{s}}{V_{p}} \Rightarrow \frac{1}{20} = \frac{V}{2400} \Rightarrow V_{s} = 120\ V$
For 100% efficiency $V_{s}i_{s} = V_{p}i_{p}$
$\Rightarrow 120 \times 80 = 2400\ i_{p} \Rightarrow i_{p} = 4\ A$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.