Q. A small coil is introduced between the poles of an electromagnet so that its axis coincides with the magnetic field direction. The number of turns is $n$ and the cross sectional area of the coil is $A$. When the coil turns through $180{^\circ}$ about its diameter, the charge flowing through the coil is $Q$. The total resistance of the circuit is $R$. What is the magnitude of the magnetic induction
A) $\frac{QR}{nA}$
B) $\frac{2QR}{nA}$
C) $\frac{Qn}{2RA}$
D) $\frac{QR}{2nA}$
Explanation
(d) Induced change $Q = - \frac{nBA}{R}\left( \cos\theta_{2} - \cos\theta_{1} \right) = - \frac{nBA}{R}\left( \cos{180{^\circ}} - \cos{0{^\circ}} \right) \Rightarrow B = \frac{OR}{2nA}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.