Question

Magnetic moment for a solenoid and a bar magnet is
(A). Equal for both.
(B). More for solenoid.
(C). More for bar magnet.
(D). None of these.

Answer 1

Hint: Magnetic moment is the magnetic strength and the orientation produced by a magnetic material. Both bar magnet and solenoid are showing great resemblance in the magnetic properties. However, the bar magnet is a permanent magnetic material while the solenoid is an electromagnetic material.

Complete step by step answer:

Solenoids are considered as one of the most commonly used electromagnets. It consists of tightly wrapped coils of wire. If the numbers of the loops are increasing, it will increase the magnetic field inside. The solenoid will behave like a bar magnet only when the current is flowing through it. The current is also made an impact on the strength of the magnetic field. An ideal solenoid has zero magnetic fields outside and uniform magnetic fields inside.
Magnetic moment can be written as,
\[\mu =m\times 2l\], where m is the pole strength and 2l is the distance between the two poles.
Magnetic moment due to current carrying solenoid can be written as,
\[\mu =I\times A\], where I is the current through the solenoid and A is the area of cross-section.
The solenoid consists of several current loops. So it shows great resemblance with the magnetic field of a bar magnet. Therefore the magnetic moment of the bar magnet is equal to the magnetic moment of the solenoid. So the correct option is A.

Additional information:
Bar magnet and solenoid possess continuous magnetic field lines. If we cut the bar magnet into two pieces, then each of the pieces will behave like small magnets since monopoles are not possible. If we cut the solenoid into two pieces, then each piece will behave like a small solenoid with a weak magnetic field. At the axial points, the magnetic field will be the same for both solenoid and bar magnet. The solenoid is an electromagnet and it will show magnetic properties only when the electric current is passed through it. It is considered that the poles of the solenoid can vary.

Note: In science experiments may be, you have seen that a battery is moving through the long solenoid coil. In this experiment, the battery may be attached to the small magnets. Since the solenoid behaves like a north and south pole, the battery will run through the solenoid continuously. The solenoid will provide a magnetic field only if the current is passing through it.