Q. A cell is connected between the points $A\ \ and\ C$ of a circular conductor $ABCD$ with $O$ as centre and angle $AOC = 60{^\circ}.$ If $B_{1}\ and\ B_{2}$ are the magnitudes of the magnetic fields at $O$ due to the currents in $ABC\ and\ \ ADC$ respectively, then ratio $\frac{B_{1}}{B_{2}}$ is

A) 1
B) 2
C) 5
D) 6
Explanation

(c) From Biot-Savart law the magnetic field at the centre is directly proportional to the length of current carrying segment.
$\therefore\frac{B_{1}}{B_{2}} = \frac{length\ of\ ABC}{length\ of\ ADC}$
$\ \ \ \ \ \ \ \ \ \ = \frac{angle\ subtended\ by\ ABC}{angle\ subtended\ by\ ADC}$
$\ \ \ \ \ \ \ \ \ \ = \frac{(360{^\circ} - 60{^\circ})}{60{^\circ}} = \frac{300}{60} = \frac{5}{1}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.