Q1) A short bar magnet placed in a horizontal plane has its alignedalong the mag

Question

Q1) A short bar magnet placed in a horizontal plane has its alignedalong the magnetic south-north direction. Null points are found onthe axis of magnet at 14cm from the center of the magnet. Theearth's magnetic field at the place is 0.36 G and the angle of dipis Zero. What is the total magnetic field on the normal bisector ofthe magnet at the same distance as the null points (i.e., 14 cm)from the center of the magnet? (At null points, field due to amagnet is equal and opposite to the horizontal component of earth'smagnetic field.)

Q2) If the bar magnet in the above problem is turned around by 180degrees, where will the new null points be located?

Explanation / Answer

Null points are found on the axis of magnet at 14cm from thecenter of the magnet. The earth's magnetic field at the place is 0.36 G and theangle of dip is Zero. 1)The magnetic field is given by B = onI Here,B = 0.36 G = 0.36 * 10-4 T,o=4 * 10-7 Tm/A and n = 1. or I = (B/o * n) = (0.36 *10-4/4 * 10-7 * 1) = 28.66 A The period of the motion is equal to the circumference of thecircle divided by the speed of the particle: T = (2m/qB) We know that T = (q/I) or (q/I) = (2m/qB) or B = (2mI/q2) Here,m = 9.1 * 10-31 kg and q = 1.6 *10-19 C or B = (2 * 3.14 * 9.1 * 10-31 * 28.66/(1.6 *10-19)2) or B = 639.8 * 107 T Therefore,the total magnetic field on the normal bisector ofthe magnet at the same distance as the null points from the centerof the magnet is B = 639.8 * 107 T. 2)When the bar magnet in the above problem is turned around by180 degrees,the new null points will be located on thehorizontal axis of the magnet.This is because the direction of themagnetic field B at any location is the direction in which acompass needle points at that location.The magnetic field lines ofa bar magnet can be traced with the aid of a compass.The magneticfield lines outside the magnet point away from the north pole andtoward the south pole.

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