20-11 The Hall Effect.
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*Some materials can be made into ‘permanent’ magnets.
These materials are said to be ferromagnetic.
Small, often microscopic regions, called domains, (at most 1mm) are aligned in ferro-magnetic substances. They are random in non-ferromagnetic substances.
Above a certain temperature, called the Curie Temperature, (1043 K for iron) no magnetism can be produced at all
*When a coil is wrapped around iron, or other ferromagnetic substance, an electromagnet can be produced.
*Electromagnets have many uses. (see p 611)
*The magnetic field inside a solenoid can be found using B0 = u0nI
When a ferromagnetic material is inside a solenoid
we use the formula:
B = u nI where u is the magnetic permeability of the material in the center of the solenoid or electromagnet.
*Measurements of magnetic materials are often made using a torus, which is an iron ring solenoid.
* Hysteresis is a curve resulting from these measurements, using a torus, where the curves do not retrace their data points of the previous curve.