Magnetism and Matter Practice Flashcards

VOCABULARY style flashcards covering the key terms and concepts from Chapter Five: Magnetism and Matter, including magnetic properties, Earth's magnetism, and classification of materials.

Magnesia

An island in Greece where magnetic ore deposits were found as early as 600 BC; the word magnet is derived from its name.

Lodestone (or leadstone)

A naturally occurring ore of iron-magnetite that translates as 'leading stone,' known for its directional and attractive properties.

Magnetic Monopoles

Isolated north or south magnetic poles, which are not known to exist in nature; if a bar magnet is cut in half, two smaller magnets are formed.

Magnetic Field Lines

Visual representations of magnetic fields that form continuous closed loops, where the tangent at a given point represents the direction of the net magnetic field $B$.

Magnetic Dipole Moment ($m$)

For a current loop, it is defined as $m = NI A$, where $N$ is the number of turns, $I$ is the current, and $A$ is the area vector.

Gauss’s Law for Magnetism

States that the net magnetic flux through any closed surface is zero ($\text{net flux } \text{φ}_B = 0$), reflecting the non-existence of magnetic monopoles.

Dynamo Effect

The process by which the earth's magnetic field is sustained by electrical currents produced by the convective motion of metallic fluids in its outer core.

Magnetic Declination ($D$)

The angle between the true geographic north and the north shown by a compass needle at a specific location.

Angle of Dip (Inclination)

The angle ($I$) that the total magnetic field $B_E$ of the earth makes with the surface (horizontal component $H_E$) of the earth.

Magnetic Meridian

The vertical plane passing through the imaginary line joining the magnetic north and south poles.

Magnetisation ($M$)

The net magnetic moment per unit volume of a sample, defined as $M = \frac{m_{net}}{V}$.

Magnetic Intensity ($H$)

A vector field relating the total magnetic field $B$ and the magnetisation $M$, defined as $H = \frac{B}{\text{μ}_0} - M$.

Magnetic Susceptibility ($\text{χ}$)

A dimensionless quantity indicating how a material responds to an external field, such that $M = \text{χ} H$.

Relative Magnetic Permeability ($\text{μ}_r$)

A dimensionless quantity related to susceptibility by $\text{μ}_r = 1 + \text{χ}$, representing the ratio of a material's permeability to that of a vacuum.

Diamagnetic Substances

Materials with a negative susceptibility ($\text{χ} < 0$) that are repelled by magnets and move from stronger to weaker parts of an external magnetic field.

Meissner Effect

The phenomenon of perfect diamagnetism in superconductors ($\text{χ} = -1$, $\text{μ}_r = 0$) where magnetic field lines are completely expelled from the material.

Paramagnetic Substances

Materials with a small positive susceptibility ($0 < \text{χ} < \text{ε}$) that are weakly attracted to a magnet and move toward regions of stronger magnetic fields.

Curie’s Law

States that for paramagnetic materials, magnetisation is inversely proportional to the absolute temperature $T$, expressed as $\text{χ} = \frac{\text{μ}_0 C}{T}$.

Ferromagnetic Substances

Materials with a large positive susceptibility ($\text{χ} \text{ >> } 1$) that get strongly magnetised in an external field and exhibit spontaneous alignment of atomic dipoles.

Domains

Macroscopic volumes in ferromagnetic materials (typically $1\text{ mm}$ in size with $10^{11}$ atoms) where individual atomic dipole moments are aligned in a common direction.

Curie Temperature ($T_c$)

The specific transition temperature above which a ferromagnetic material becomes paramagnetic.

Retentivity (Remanence)

The value of the magnetic field $B$ remaining in a material when the external magnetic intensity $H$ is reduced to zero.

Coercivity

The magnitude of the reverse magnetic intensity $H$ required to reduce the residual magnetic field $B$ in a material back to zero.

Hysteresis

The phenomenon where the magnetic field $B$ of a material lags behind the external magnetic intensity $H$ and depends on the prior magnetic history of the sample.

Electromagnets

Magnets with cores made of ferromagnetic materials (like soft iron) possessing high permeability and low retentivity, allowing them to be switched on and off easily.