Question

Which of the following is a source of magnetic field?
A) Isolated magnetic pole
B) Static electric charge
C) Current loop
D) Moving light source

Answer 1

Hint: A magnetic field is a region around a magnetic material or moving electric charge that consists of a north and a south pole where its magnetic force is felt. From the above options, only a current-carrying coil satisfies the two conditions of a magnetic field.

Complete step by step solution:
Let us go through all the given options one after the other. An isolated magnetic pole can never exist, north and south poles of a magnet can never be isolated. A static electric charge does not have a moving current; it is just an accumulation of cations or anions, this does not cause a magnetic field. A moving light source does not carry any sort of charge or magnetic force or any sort of force hence it cannot be a source of the magnetic field.

A current-carrying loop has a charge moving through it and where there is the current flowing there is a magnetic field. The magnetic field again has both north and south poles. A current loop satisfies both the conditions of a magnetic field definition.

Hence option (C), current loop is the correct option.

Additional information: Motors are the most common application of magnetic force on current-carrying wires. Motors contain loops of wire in a magnetic field. When current is passed through the loops, the magnetic field exerts a torque on the loops, which rotates a shaft. Electrical energy is converted into mechanical work in the process.

Note: A magnetic pole can never be isolated, it is only a hypothetical situation. Earth on its own has a magnetic field of itself with two magnetic poles. These magnetic poles or magnetic fields of the earth are what makes a compass work to give us directions.