Definitions [15]
Define Curie temperature.
The temperature above which a ferromagnetic substance becomes paramagnetic is called curie temperature.
Define magnetization.
The ratio of magnetic moment to the volume of the material is called magnetization.
Define magnetic intensity.
The ratio of the strength of the magnetizing field to the permeability of free space is called magnetic intensity.
The ratio of the magnitude of the total field inside the material to that of the intensity of the magnetising field is called magnetic permeability.
The ratio of magnetic permeability of the material (μ) and magnetic permeability of free space (μ₀) is called relative permeability.
The ratio of the strength of the magnetising field to the permeability of free space is called magnetic intensity.
The ratio of the magnitude of intensity of magnetisation to that of magnetic intensity is called magnetic susceptibility.
The magnetic moment developed per unit volume of a material when placed in a magnetising field is called the 'intensity of magnetisation'.
The ability of a magnetising field to magnetise a material medium is called magnetising field intensity.
The ratio of magnetic moment to the volume of the material is called magnetisation.
The total magnetic field inside a magnetic material, which is the sum of the external magnetising field and the additional magnetic field produced due to magnetisation of the material, is called magnetic induction.
The magnetic field that exists in a vacuum and induces magnetism is called a magnetising field.
Substances which when placed in a magnetising field are strongly magnetised in the direction of the magnetising field are called ferromagnetic substances.
Substances which when placed in a magnetic field are feebly magnetised in a direction opposite to that of the magnetising field are called diamagnetic substances.
Substances which when placed in a magnetic field are feebly magnetised in the direction of the magnetising field are called paramagnetic substances.
Formulae [6]
B = μ0(H + M)
-
SI unit: tesla (T)
M = χH
or
χ = HM
B = μH
-
SI unit: H/m
μr = \[\frac {μ}{μ_0}\]
M = \[\frac {\text {magnetic moment}}{\text {volume}}\]
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SI unit: A/m
H = nI
where n is the number of turns per unit length and I is current.
-
SI unit: A/m
Theorems and Laws [3]
For ferromagnetic substances above the Curie temperature, the magnetic susceptibility is inversely proportional to (T − TC), where TC is the Curie temperature. Mathematically,
On heating beyond the Curie temperature (TC(iron) = 770 °C), ferromagnetic substances get converted into paramagnetic materials.
The magnetic susceptibility of a paramagnetic material varies inversely with its absolute temperature. Mathematically,
On cooling, paramagnetic substances get converted to ferromagnetic materials at the Curie temperature.
Curie's Law describes the relationship between the magnetic susceptibility (χ) of a paramagnetic material and its temperature (T). According to Curie's Law, the magnetic susceptibility is directly proportional to the inverse of the absolute temperature
\[\chi=\frac{C}{T}\]where:
(χ) is the magnetic susceptibility.
C is the Curie constant, which is specific to each material.
T is the absolute temperature in kelvin.
Key Points
- A current-carrying loop behaves like a magnetic dipole (bar magnet)
- Polarity Rule
Anticlockwise current → North pole (upper face)
Clockwise current → South pole (lower face)
- Diamagnetic substances are weakly repelled and have negative susceptibility.
- Paramagnetic substances are weakly attracted and obey Curie law.
- Ferromagnetic substances are strongly attracted and contain domains.
- Ferromagnets become paramagnetic above the Curie temperature.
- The comparison table is the most important revision tool for board preparation.
Important Questions [27]
- Obtain an Expression for the Magnitude of Magnetic Moment of a Revolving Electron
- Calculate the Magnitude of Magnetic Moment Associated with the Coil.
- Show that the orbital magnetic dipole moment of a revolving electron is eVr2
- The Electron in the Hydrogen Atom is Moving with a Speed of 2.3106 M/S in an Orbit of Radius 0.53 å. Calculate the Period of Revolution of the Electron. (π = 3.142)
- Draw the Diagrams Showing the Dipole Moments in Paramagnetic Substance When External Magnetic Field is (A) Absent (B) Strong
- An Electron in an Atom Revolves Around the Nucleus in an Orbit of Radius 0.53 Å. If the Frequency of Revolution of an Electron
- State SI unit of Magnetization.
- Define Magnetization.
- The Magnetic Moment of a Magnet of Dimensions 5 Cm × 2.5 Cm × 1.25 Cm is 3 Am2. Calculate the Intensity of Magnetization.
- State formula and S.I. unit of Magnetization.
- Find the magnetization of a bar magnet of length 10 cm and cross-sectional area 4 cm^2, if the magnetic moment is 2 Am^2.
- Define Magnetic Intensity.
- Define magnetic intensity.
- Define magnetization.
- What is magnetic susceptibility?
- State unit and dimensions of Magnetic susceptibility.
- Give Any ‘Two’ Points of Differences Between Diamagnetic and Ferromagnetic Substances.
- The Magnetic Susceptibility of Annealed Iron at Saturation is 4224. Find the Permeability of Annealed Iron at Saturation
- Which of the Following Substances is Ductile?
- 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
- Distinguish between ‘paramagnetic’ and ‘ferromagnetic’ substances.
- 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?
- 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 ironmagnet
- Distinguish between diamagnetic and paramagnetic substances.
- Explain ferromagnetism on the basis of the domain theory.
- What happens to a ferromagnetic substance heated above Curie temperature?
- The Susceptibility of Magnesium at 300 K is 1.2 X 10 -5 . What Will Be Its Susceptibility at 200 K.
