MATHEMATICAL PROPERTIES

• Magnetic fields have direction. As a result we must pay special attention to directions, and vector calculations.

• Magnetic fields pass through space.

 

• resistivity of materials decreases with temperature

• Amperes Circuit Law

 

• Flux density can be calculated for low H values. As the value climbs the relationship becomes non-linear.

 

• Permeability,

 

• Permeability is approximately linear for smaller electric fields, but with larger magnetic fields the materials saturate and the value of B reaches a maximum value.

 

Figure 23.1 Saturation for a mild steel (approximately)

 

Figure 23.2 Magnetization curves (Sen, 1989)

• Flux density about a wire

 

 

• Flux and flux density,

 

 

• When a material is used out of the saturation region the permeabilities may be written as reluctances,

 

• Electric circuit analogy

 

• Example,

 

• Faraday’s law,

 

• Field energy,

 

• Force can be derived from the energy,

 

 

• The basic property of induction is that it will (in the presence of a magnetic field) convert a changing current flowing in a conductor to a force or convert a force to a current flow from a change in the current or the path.

 

Figure 23.3 The current and force relationship

• We will also experience an induced current caused by a conductor moving in a magnetic field. This is also called emf (Electro-Motive Force)

 

Figure 23.4 Electromagnetically induced voltage

 

• Hysteresis