Q. A step-down transformer is connected to main supply $200V$ to operate a $67V,\ 30W$ bulb. The current in primary is
A) $3\ A$
B) $1.5\ A$
C) $0.3\ A$
D) $0.15\ A$
Explanation
(d) $V_{p} = 200\ V,\ V_{s} = 6V$
$P_{out} = V_{s}i_{s} \Rightarrow 30 = 6 \times i_{s} \Rightarrow i_{s} = 5\ A$
From $\frac{V_{s}}{V_{p}} = \frac{i_{p}}{i_{s}} \Rightarrow \frac{6}{200} = \frac{i_{p}}{5} \Rightarrow i_{p} = 0.15\ A$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.