Electromagnetism

magnetic materials

can be magnetised or will be attracted to a magnet

magnetic field

A region in space where a magnetic force Is experienced by a moving charge

dipole

a magnetic North Pole and a magnetic South Pole separated by some small distance

right hand rule

used for finding the curved direction of a magnetic field using the direction of the current

magnetomotive force

causes the magnetic field, but not a force itself MMF = NI (Number of Turns x Electric current)

magnetic field strength

magnetising force per unit length H = F/L = NI/L

Magnetic induction

measures the actual magnetic field strength inside of a material, taking into account both the applied force H and the materials magnetic response 𝑩 = 𝝁𝑯 (Wb/m2 or Tesla or N/(A.m))

permeability of free space μ

measure of the resistance of a material against the formation of a magnetic field

relative permeability

the measure of the degree of which a material can be magnetised calculated as a ratio permeability in a material to the permeability in a vacuum: 𝝁𝒓 = 𝝁/𝝁𝒐 and in air, 𝝁𝒓 ≈ 𝟏

magnetisation

measures the extent to which a material is magnetised measured in A/M 𝑩 = 𝝁𝒐(𝑯 + 𝑴)

magnetic susceptibility 𝝌𝒎

the measure of which a material is attracted to or repelled from a magnetic field 𝑀= 𝝌𝒎𝐻

magnetic flux

the measure of the total number of magnetic field lines passing through a given area

𝑩 ⋅ 𝑨 = 𝑩𝑨𝒄𝒐𝒔𝜽

Faradays experiments

• a magnetic field does not induce a current in a wire

• a changing magnetic field does induce a current in a wire

EMF electromagnetic force

proportional to the rate of change of magnetic flux, through any surface bounded by that circuit

Diamagnetic

Show no small magnetic fields when no magnetic field is applied, and then show a small negative when a field is applied

Paramagnetic

Show random magnetic fields when no magnetic field is applied, and then show a small positive when a field is applied

Ferromagnetic/Ferrimagnetic

Show random magnetic fields when no magnetic field is applied, and then show a large positive when a field is applied

Hysteresis

when you align the domains of a material through magnetising then remove the magnetising effect, some alignment remains. as that material resists magnetic change

Coercivity

the resistance of a magnetic material to changes in magnetization, equivalent to

the field intensity necessary to demagnetize the fully magnetized material.

Hard Magnetic Materials

-- large coercivities

-- used for permanent magnets

-- example: tungsten steel -- Hc = 5900 A/m)

Soft magnetic materials

-- small coercivities

-- used for electric motors

-- example: commercial iron 99.95 Fe