Magnetism and Matter

Vocabulary practice flashcards covering fundamental definitions, formulas, properties, and classifications of magnetic materials and phenomena from the Magnetism and Matter lecture notes.

Magnetite ($Fe_3O_4$)

A natural ore with the chemical formula $Fe_3O_4$, known as a natural magnet.

Permanent Magnet

A magnet made of hard steel or magnetic alloys such as alnico ($Al + Ni + Co$), cobalt steel, or tungsten that exhibits magnetic properties for an infinite time and cannot be easily demagnetized.

Alnico

A magnetic alloy composed of aluminium, nickel, and cobalt ($Al + Ni + Co$) used to construct permanent magnets.

Temporary Magnet

A magnet made of soft iron or soft steel that remains magnetized only while a magnetising force is present and loses almost all magnetic properties once that force is removed.

Attractive Property

The property of a magnet to attract magnetic substances such as iron, steel, cobalt, and nickel, with the attractive force being maximum at the ends of the magnet.

Directive Property

The property of a bar magnet suspended from its centre to always align itself along a definite direction, specifically the north-south direction.

Magnetic Pole

The regions at both ends of a magnet (north pole and south pole) where the force of attraction is at its maximum.

Magnetic Induction

The phenomenon wherein a magnetic material, such as a rod of soft iron, behaves like a magnet when brought near a powerful magnetic pole.

Surest Test for Magnetism

Repulsion, because a magnet attracts both opposite poles and unmagnetized magnetic materials, but only repels a like magnetic pole.

Magnetic Pole Strength ($q_m$ or $m$)

The strength of a magnetic pole to attract substances towards itself, given by $q_m = \frac{F}{B}$, with units of $\text{Newton}/\text{Tesla}$ or $\text{Ampere}\times\text{meter}$, dimension $[AL]$, and scalar nature.

Effective Length ($\vec{l}$)

The distance between the two poles of a magnet, equal to approximately $\frac{5}{6}$ of its geometrical length, represented as a vector directed from the south pole to the north pole.

Magnetic Dipole

A system consisting of two unlike poles of equal pole strength separated by a limited distance, exemplified by a bar magnet, current loop, or magnetic needle.

Magnetic Dipole Moment ($M$)

The product of the pole strength and the effective length of a magnet ($M = m \times l$ or $M = q_m \times 2l$), directed from the south pole to the north pole with the unit $\text{Ampere}\times\text{meter}^2$.

Magnetic Lines of Force

Imaginary continuous closed paths along which an isolated unit north pole would move; directed from north to south outside the magnet and from south to north inside the magnet.

Neutral Point

A point where opposing magnetic fields completely cancel each other out, resulting in a net magnetic force of zero.

Intensity of Magnetisation ($I$)

The magnetic moment developed per unit volume of a magnetized substance ($I = \frac{M}{V}$), which is a vector quantity with the unit $\text{Ampere}/\text{meter}$.

Magnetizing Field ($H$)

The external magnetic ability to magnetize a material, representing the part of magnetic induction produced solely by external currents in a vacuum ($H = \frac{B_0}{\mu_0}$).

Magnetic Susceptibility ($\chi$)

The dimensionless scalar ratio of the intensity of magnetisation ($I$) to the magnetizing field ($H$), given by $\chi = \frac{I}{H}$.

Magnetic Permeability ($\mu$)

The ability of a medium to conduct magnetic lines of force through it, defined as $\mu = \frac{B}{H}$, with units of $\text{Henry}/\text{meter}$ or $\text{Weber}/(\text{Ampere}\times\text{meter})$.

Relative Magnetic Permeability ($\mu_r$)

The dimensionless ratio of the permeability of a substance to that of free space ($\mu_r = \frac{\mu}{\mu_0}$), indicating how easily magnetic fields penetrate the material.

Diamagnetic Substance

A substance that is weakly repelled by a magnetic field, moves from stronger to weaker field regions, has $\mu_r < 1$ and a small negative $\chi$, and exhibits magnetism due to paired orbital electrons (e.g., bismuth, water, mercury).

Paramagnetic Substance

A substance that is weakly attracted by a magnetic field, moves from weaker to stronger field regions, has $\mu_r > 1$ and a small positive $\chi$, and obeys Curie's law ($\chi \propto \frac{1}{T}$).

Ferromagnetic Substance

A substance strongly magnetized in the direction of an applied field due to the formation of magnetic domains, possessing $\mu_r \gg 1$ and a high positive $\chi$ (e.g., iron, cobalt, nickel).

Curie-Weiss Law

The law stating that the magnetic susceptibility of a ferromagnetic material above its Curie temperature varies inversely with temperature: $\chi = \frac{C}{T - T_c}$.

Curie Temperature ($T_c$)

The critical temperature above which a ferromagnetic substance loses its ferromagnetism and converts into a paramagnetic substance.