Magnetism Flashcards
Expression for magnetic induction at a a point in the axis at a distance x from the centre of a circular coil of radius a, carrying current i
B= μ0ia*a/(2(a^2 + x^2)^(3/2))
= (μ0/4π)*(2M/(x^3))
Properties of magnets
Directive property
Attractive property
Earth behaves as a magnet with magnetic field pointing approximately from geographical south to geographical north.
Magnetic monopoles do not exist.
Magnetism has its origin in circulating charges within the atoms of any substance.
Expression for magnetic dipole moment
M=IA
Magnetic dipole moment of a revolving electron - Derivation
T= 2πr/v i= e/T M= evr/2
What is the direction of magnetic moment of a rotating electron?
Into the plane of paper
Negative charged electrons move in anti-clockwise direction leading to clockwise current.
Relation between orbital angular momentum and orbital magnetic moment of an electron
__ __
M = -(e/2m)*L
In opposite directions
Define Gyromagnetic ratio
The ratio of magnetic dipole moment with angular momentum of revolving electron is called Gyromagnetic ratio.
Expression for Gyromagnetic ratio
M/L = e/2m
Value of Gyromagnetic ratio
8.8 * 10^8 C/kg
Define magnetization
The net magnetic dipole moment per unit volume of the sample is called as the magnetization of the sample.
Expression for magnetization
___ ___
Mz= Mnet/Volume
What is the unit of magnetization?
A/m
Is magnetization a scalar or vector quantity?
Vector
Dimensions of magnetization
[L-1 M0 T0 I1]
Define saturation of the sample
Complete alignment of the atomic dipole moment is called saturation of the sample.
State Curie law
Curie law states that, magnetization of a paramagnetic sample s directly proportional to the external magnetic field and inversely proportional to the absolute temperature.
What is the equation for Curie law?
Mz= C*Bext /T
What is magnetic intensity?
The vector quantity in terms of which strength of the magnetic field at a point can be given is known as magnetic intensity.
Relation between magnetic field and magnetic intensity
Bo=μο*Η
Unit of H
A/m
Dimensions of H
[L-1 M0 T0 I1]
Relation between magnetization and magnetic intensity
Mz= χH
Dimensions of susceptibility
Unitless, dimensionless
χ for paramagnetic materials
Small and positive
χ for diamagnetic materials
Small and negative
χ for ferromagnetic materials
Large and positive
Expression for magnetization of a ferromagnetic substance
B= μo (1+χ) H
Expression for relative magnetic permeability of a substance
μr= 1+ χ
What are diamagnetic substances?
Substances that are weakly repelled by a magnet are called diamagnetic substances.
How does a diamagnetic substance align itself when suspended freely in magnetic field?
It aligns itself at right angles to the direction of field.
Define superconductors
Superconductors are metals which when cooled to very low temperatures exhibit both perfect conductivity perfect diamagnetism.
What is Messiner effect?
The phenomenon of perfect diamagnetism in superconductors is called the Messiner effect.
Properties of diamagnetic substances
Pg250
Examples of diamagnetic substances
Ag, Pb, Si, N2, NaCl, Bi, Cu, Sb, Au, Hg, H2O, air, H2
What are paramagnetic substances?
Substances which are weakly attracted by a magnet are called paramagnetic substances.
What are atomic magnets?
In paramagnetic substance, the magnetic dipole moments of all the electrons do not cancel out resulting in some dipole moment for an atom so that each atom of a paramagnetic substance is equivalent to tiny magnetic dipole called atomic magnets.
Give reasons: Atomic magnets cannot be used to make permanent magnets.
Lose their magnetism on removal of external electric field.
List the properties of paramagnetic substances.
Pg 251
What happens when a thin rod of paramagnetic substance is freely suspended in magnetic field?
Comes to rest with length parallel to direction of external electric field.
Examples of paramagnetic substances
Al, Mn, Cr, Pt, O2, Na, Ca, Li, CuCl2, W, Nb, etc
How does the susceptibility of a paramagnetic substance depend on temperature?
The susceptibility of a paramagnetic substance varies inversely with temperatures.
χ α 1/Τ
What are ferromagnetic substances?
Substances which are strongly attracted by a magnet are known as ferromagnetic substances.
Give reasons: Permanent magnets are made of ferromagnetic substances.
Retain magnetism even after removal of external magnetic field.
Properties of ferromagnetic substances
Pg 251
How does a thin rod of ferromagnetic substance in an external magnetic field align itself?
Comes to rest with axis parallel to magnetic induction between two poles.
Define domains
The region of a ferromagnetic substance on which all magnetic moments are aligned in the same direction are known as domains.
Give reasons: all Magnetic dipoles have magnetic dipole moments in the same direction
Strong exchange coupling between neighboring atoms in domain.
What is flipping or domain rotation?
When external applied magnetic field to a ferromagnetic substance is large, the dipole moments of non-alliance dipoles rotate in the direction of applied field. This process is known as flipping or domain rotation.
Does temperature affect degree of magnetization of a ferromagnetic substance?
Yep
Explain domain theory.
Pg 252
Define curie temperature
The temperature at which domain structure is destroyed and the ferromagnetic system looses its magnetism and above which a ferromagnetic substance is converted into a paramagnetic substance is called Curie Temperature.
