Question

Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it. Describe some salient features of magnetic lines of force concept.

Answer 1

Hint: A conductor behaves like a magnet when placed in an external magnetic field. Current carrying loops behave like bar magnets in the case. The external magnetic field, and the compass needle; both have their associated lines of field, called magnetic field lines. This modifies the already existing effect of earth’s magnetic field on the needle, and a deflection results in the compass needle.

Complete step by step answer:
When an electric current passes through a conductor, it behaves like a bar magnet and an induced EMF is created, which then generates magnetic lines of force around it. Thus, when a magnetic compass needle that is pointing in the north-south direction according to the earth's magnetic field, starts showing deflection with respect to the strength of the magnetic field that is a superposition of magnetic field created by the current carrying conductor and of earth.

Features of magnetic lines of force:
The magnetic field at any given point is specified by both a direction and a magnitude.
Magnetic lines of force start from the North Pole and end at the South Pole.
Two magnetic field lines never intersect each other, and they are continuous along the axis of the electromagnetic conductor.
The magnetic field lines are uniform and strong at the center or inside of the conductor. The lines diverge as they move away from the conductor and as the distance increases. Eventually, the strength of the magnetic field is strong inside the magnet and they weaken as the closeness decreases.


Note:
When a magnetic compass needle points the direction North and South in the absence of a nearby magnet or a current carrying loop, it is under the effect of the Earth's magnetic field only. But in the presence of a magnet or a current loop, which also has a magnetic field associated with it, the Earth's magnetic field near the compass is modified and the needle is deflected from North-South direction.