Advertisements
Advertisements
Question
What happens to a ferromagnetic material when its temperature increases above curie temperature?
Solution
A ferromagnetic material is made up of small regions known as domains. The atomic magnetic moments of nearest-neighbour atoms interact strongly within each domain via exchange interaction, a quantum mechanical phenomenon, and align parallel to each other even in the absence of an external magnetic field. As a result, a domain is spontaneously magnetised to saturation.
Only up to a specific temperature does the material keep its domain structure. When heated, the increased thermal agitation opposes spontaneous domain magnetization. Finally, at a critical temperature known as the Curie point or Curie temperature, thermal agitation overcomes the exchange forces and maintains the atomic magnetic moments randomly oriented. As a result, the material becomes paramagnetic above the Curie point. The ferromagnetic to paramagnetic transition is a transition from order to disorder. The material becomes ferromagnetic again when cooled below the Curie point.
RELATED QUESTIONS
Give any ‘two’ points of differences between diamagnetic and ferromagnetic substances.
An iron rod of the area of cross-section 0.1m2 is subjected to a magnetizing field of 1000 A/m. Calculate the magnetic permeability of the iron rod. [Magnetic susceptibility of iron = 59.9, magnetic permeability of vacuum = 4π x 10-7 S. I. unit]
The susceptibility of magnesium at 200 K is 1.8 x 10-5. At what temperature will the susceptibility decrease by 6 x 10-6?
Show diagrammatically the behaviour of magnetic field lines in the presence of (i) paramagnetic and (ii) diamagnetic substances. How does one explain this distinguishing feature?
A meter gauge train is heading north with speed 54 km/hr in earth's magnetic field 3 x 10-4T. The e.m.f. induced across the axle joining the wheels is ..........
(a) 0.45 mV
(b) 4.5 mV
(c) 45 mV
(d) 450 m V
Which of the following substances are para-magnetic?
Bi, Al, Cu, Ca, Pb, Ni
The susceptibility of a magnetic material is − 2.6 × 10−5. Identify the type of magnetic material and state its two properties.
The magnetic susceptibility of platinum is 0.0001. It's relative permeability is:
Which of the following statements is correct for diamagnetic materials?
Choose the correct option:
A rectangular magnet suspended freely has a period of oscillation equal to T. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely. Its period of oscillation is T′, the ratio of T′/T is ______.
Choose the correct option:
A magnetising field of 360 Am−1 produces a magnetic flux density (B) = 0.6T in a ferromagnetic material. What is its permeability in Tm A−1?
A rod of magnetic material of cross-section 0.25 cm2 is placed in a magnetizing field of intensity 4000 A/m-1. The magnetic flux passing through the rod is 25 × 10-6 Wb. Find out
(a) relative permeability
(b) magnetic susceptibility and
(c) magnetisation of the rod.
For a paramagnetic substance, the magnetic susceptibility is ______.
Magnetization of the sample is ______.
If a magnetic field is applied to a liquid in one arm of a narrow U-tube, the liquid level in that arm is lowered. The liquid in U-tube arm is ______.
Relative permittivity and permeability of a material are `epsilon_"r"` and `µ_"r"` respectively. Which of the following values of these quantities are allowed for a diamagnetic material?
The materials having negative magnetic susceptibility are ____________.
The product of magnetic susceptibility (`chi`) and absolute temperature (T) is constant for a ____________.
Above the curie temperature the susceptibility of ferromagnetic substance varies ____________.
A sphere of gold when brought towards a powerful magnet experiences ____________.
Which graph shows the variation of magnetic susceptibility (`chi`) with magnetizing field (H) for a paramagnetic substance?
Why is diamagnetism, in contrast, almost independent of temperature?
Is the permeability of a ferromagnetic material independent of the magnetic field? If not, is it more for lower or higher fields?
Would the maximum possible magnetisation of a paramagnetic sample be of the same order of magnitude as the magnetisation of a ferromagnet?
What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player, or for building ‘memory stores’ in a modern computer?
A certain region of space is to be shielded from magnetic fields. Suggest a method.
A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field B in the core for a magnetising current of 1.2 A?
The given figure represents a material which is ______.
Assertion: The ferromagnetic substance do not obey Curie’s law.
Reason: At Curie point a ferromagnetic substance start behaving as a paramagnetic substance.
The coercivity of a small magnet where the ferromagnet gets demagnetized is 3 × 103 Am–1. The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetized when inside the solenoid, is ______.
Assertion: A paramagnetic sample display greater magnetisation (for the same magnetic field) when cooled.
Reason: The magnetisation does not depend on temperature.
Metals getting magnetised by orientation of atomic magnetic moments in external magnetic field are called ______.
Two identical bar magnets are fixed with their centres at a distance d apart. A stationary charge Q is placed at P in between the gap of the two magnets at a distance D from the centre O as shown in the figure. The force on the charge Q is ______.
For a diamagnetic material
If a charged particle at rest experience no electromagnetic force
According to the Atomic theory, on heating a magnet, the thermal energy of the elementary magnet ______
A long solenoid has 1000 turns per metre and carries a current of 1 A. It has a soft iron core of µr = 1000. The core is heated beyond the Curie temperature, Tc.
- The H field in the solenoid is (nearly) unchanged but the B field decreases drastically.
- The H and B fields in the solenoid are nearly unchanged.
- The magnetisation in the core reverses direction.
- The magnetisation in the core diminishes by a factor of about 108.
From molecular view point, discuss the temperature dependence of susceptibility for diamagnetism, paramagnetism and ferromagnetism.
A uniform magnetic field gets modified as shown in figure when two specimens A and B are placed in it.
 |
 |
| (a) | (b) |
- Identify the specimen A and B.
- How is the magnetic susceptibility of specimen A different from that of specimen B?
An ammeter of resistance R gives a full-scale deflection when a current of 2 A passes through it. If it is measured with a maximum current of 10 A, the required shunt is ______.
- Assertion (A): Diamagnetic substances exhibit magnetism.
- Reason (R): Diamagnetic materials do not have a permanent magnetic dipole moment.
What is magnetic hysterisis?
Explain the Domain theory in brief.
Magnetic susceptibility of a diamagnetic substance ______.
