Question

The magnetic length of a bar magnet is 10 cm then its geometric length is:
A. 10 cm
B. 12 cm
C. 5 cm
D. 6 cm

Answer 1

Hint: Magnetic field is the space around the magnet where the effect of magnet can be felt by another magnet or iron piece. Magnetic fields can also be produced by a moving charge whose intensity can be determined by the velocity and magnitude of charge or using a magnet having definite pole strength. The S.I unit of magnetic field is Tesla (T) whereas the C.G.S unit is Gauss (G).

Complete answer:
Inside the earth, we can find several natural occurring materials which produce the magnetic field around them naturally. The reason for this is the arrangement of domain inside the magnet. Such a material is called a natural magnet and bar magnet is an example of this. Every material of magnet has a defined magnetic field associated with it. This can be measured by its pole strength. Hence the amount of magnetic field a magnet will produce is directly associated with its pole strength.

Geometric length: It may be defined as the length which appears to us or the actual length of magnet.

Magnetic length: It may be defined as the distance between two poles of the magnet and poles could actually be defined as the point inside the magnetic material from where maximum magnetic lines are getting originated.

This can be located by drawing tangents at the magnetic lines of the field where they cut the surface of the magnet, as shown in figure.

Thus, we can see that magnetic length is 2M which is surely less than 2L.
Hence, geometric length is always greater than magnetic length.

So, the correct answer is “Option B”.

Note:
Always remember that the geometric length of a magnet is always little greater than the magnetic length because it’s always assumed that the poles of the magnet lie little bit inside the material. But practically this distance is very less and one can neglect while doing calculations.