Question

Which of the following processes will not produce new magnetic poles?
A) Cutting a magnet bar in half
B) Turning on current in a solenoid
C) Running a current through a straight wire
D) Placing an iron rod in contact with a magnet

Answer 1

Hint: There are two poles of a magnet. They interact with each other by virtue of magnetic fields. However only the presence of magnetic fields does not ensure the presence of magnetic poles. Magnetic fields sometimes can exist without magnetic poles.

Complete step by step answer:
When we hold a simple magnet, let’s say, a bar magnet and dip it inside a heap of iron filings, we will see that iron filings stick to the magnet at two points near the ends.
The point region where the attracting power of a magnet is maximum is considered as the pole of a magnet and the region where there is no force is called the neutral region of the magnet.
Every magnet has two poles of equal strength but opposite nature and poles cannot exist iso lately that is poles always occur in pairs. Whenever we break a magnet into a number of pieces, each piece acts as an individual magnet consisting of two poles. This justifies our option A, cutting a magnet bar in half will result in magnets with both the poles.
A solenoid is a spring shaped conducting instrument with two faces. When current is passed through a solenoid, it acts like a magnet with one face acting as south-pole and the other acting as north-pole. Thus when a solenoid carries current, it behaves like a magnet having two poles. This justifies option B.
Magnetisation is a phenomenon by virtue of which magnetic objects such as rods of iron can be turned into temporary magnets. The process of magnetisation involves rubbing an iron rod with a strong magnet or placing in close contact with it. This induces pole formation temporarily inside the iron rod, making one pole act as north-pole and the other pole acting as south-pole. This justifies our option D.
However, when we look at a straight conductor carrying current, it only produces a magnetic field. If it is carrying current upwards, an anticlockwise magnetic field is produced and when the current is being carried downwards, a clockwise magnetic field is produced as per Maxwell’s cork-screw rule.

Thus the correct answer is C, a current carrying conductor does not produce magnetic poles, rather it only generates a magnetic field.

Note: A solenoid produces two poles when current is passed through it. But how do we know which face acts as south-pole and which pole acts as north-pole. The trick is the face of the coil through which flow of current seems anticlockwise becomes the north-pole and the face through which current flow seems clockwise becomes south-poles of the magnetic dipole.