Question

What change in the deflection of the compass needle placed at a point near current carrying straight conductor shall be observed if the
(a) Current through the conductor is increased?
(b) Direction of current in the conductor reversed?
(c) Compass is moved away from the conductor?

Answer 1

By reading the question we can see that the question is related to magnetic field and its applications, thus to solve we will at first understand the role of changing of current through the current carrying wire and the role of relation between magnetic flux density and current.

Complete answer:
Let us understand why the compass gets deflected due to current, when there is a current carrying conductor placed in close contact to the compass (which is made up of magnetized iron), the magnetic field formed due to the conductor disturbs the weak field between the earth’s magnet and the compass. The field formed due to the current carrying wire is in concentric circles and causes based on the orientation of the magnet, one end will attract and another will repel.

(a) Now the deflection is increased as the current is increased as electric field is directly proportional to magnetic field. Thus, taking into account our observations, we can say that the deflection will increase when the current in the conductor is increased.

(b) Now as the current carrying conductor forms a magnetic field, it has its own poles and as the direction of current is reversed in the conductor, the direction of deflection will be reversed when current direction is reversed.

(c) Now as the compass is moved away from the wire, the influence of the wire’s magnetic field on the compass gets decreased and thus the deflection of the compass gets decreased.

Note: Remember the fact that electric field is produced due to stationary charges and that magnetic field is produced by moving or dynamic charges. Also remember that a compass is made up of magnetized iron and it always points towards the earth’s pole.