Magnetic Properties of Matter Physics - Magnetic Properties of Matter

Electromagnets are made of soft iron because soft iron has:

1. High retentivity and high coercive force.
2. High retentivity and low coercive force.
3. Low retentivity and high coercive force.
4. Low retentivity and low coercive force.

The permanent magnetic moment of the atoms of a material is not zero. The material:

1. Must be paramagnetic.
2. Must be diamagnetic.
3. Must be ferromagnetic.
4. May be paramagnetic.

The permanent magnetic moment of the atoms of a material is zero. The material:

1. Must be paramagnetic.
2. Must be diamagnetic.
3. Must be ferromagnetic.
4. May be paramagnetic.

When a ferromagnetic material goes through a hysteresis loop, the magnetic susceptibility:

1. Has a fixed value.
2. May be zero.
3. May be infinity.
4. May be negative.

The desirable properties for making permanent magnets are:

1. High retentivity and high coercive force.
2. High retentivity and low coercive force.
3. Low retentivity and high coercive force.
4. Low retentivity and low coercive force.

The coercive force for a certain permanent magnet is 4.0 × 10⁴A/m. Thia magnet is placed inside a long solenoid of 40 turns/cm and a current is passed in the solenoid to demagnetise it completely. Find the current.

The susceptibility of magnesium at 300K is 1.2 × 10^-5. At what temperature will the susceptibility increase to 1.8 × 10^-5?

The susceptibility of annealed iron at saturation is 5500. Find the permeability of annealed iron at saturation.

Assume that each iron atom has a permanent magnetic moment equal to 2 Bohr magnetons (1 bohr magneton equals 9.27 × 10^-24A-m²). The density of atoms in iron is 8.52 × 10²⁸ atoms/m³.

1. Find the maximum magnetization I in a long cylinder of iron.
2. Find the maximum magnetic field B on the axis inside the cylinder.

Can we have magnetic hysteresis in paramagnetic or diamagnetic substances?

What are the advantages of using soft iron as a core, instead of steel, in the coils of galvanometers?

The magnetic intensity Hat the centre of a long solenoid carrying a current of 2.0A, is found to be 1500A/m. Find the number of turns per centimetre of the solenoid.

Why is it not possible to make permanent magnets from paramagnetic materials?

A rod is inserted as the core in the current-carrying solenoid of the previous problem.

1. What is the magnetic intensity H at the centre?
2. If the magnetization I of the core is found to be 0.12Nm, find the susceptibility of the material of the rod.
3. Is the material paramagnetic, diamagnetic or ferromagnetic?

When a ferromagnetic material goes through a hysteresis loop, its thermal energy is increased. Where does this energy come from?

To keep valuable instruments away from the earth's magnetic field, they are enclosed in iron boxes. Explain.

When a dielectric is placed in an electric field, it gets polarized. The electric field in a polarized material is less than the applied field. When a paramagnetic substance is kept in a magnetic field, the field in the substance is more than the applied field. Explain the reason of this opposite behaviour.

A rod, when suspended in a magnetic field, stays in the east-west direction. Can we be sure that the field is in the east-west direction? Can it be in the north-south direction?

Do permeability and relative permeability have the same dimensions?

The property of diamagnetism is said to be present in all materials. Then, why are some materials paramagnetic or ferromagnetic?