Question

An electric cable is laid out horizontally and is carrying current from north to south, at the magnetic equator. The position of the null point from the cable is :

• A. Vertically upward
• B. Vertically downward
• C. Eastward
• D. Null point cannot be achieved

Answer 1

The correct option is D Null point cannot be achieved


The magnetic field line around the straight wire is shown above. The direction of magnetic field at a point, will be along the tangent drawn to the field line, at that point.

At the magnetic equator, the earth's magnetic field is directed horizontally, from south to north.

Since, the magnetic field of earth is always perpendicular to the field of the wire, for the given configuration, there is no point where they both can cancel each other. So, the neutral point will not be obtained for any position.

The direction of magnetic field due to the wire is vertical, while due to earth is from south to north.

Hence, option $\left(D\right)$ is the correct answer.