The article defines the other basic principles of magnetism, magnetic and inductor components – Magnetic Induction, Magnetic Flux and Faraday’s Law.

**Magnetic induction B**

A potential is induced in a conductor loop if the magnetic field passing through the conductor loop changes with time.

The surge in potential over the area of the loop is known as the magnetic induction **B**. Like the magnetic field strength, the magnetic induction **B** is a vector quantity.

The following relationship applies for the magnetic induction** B**:

The magnetic induction (**B**) is the quotient of the induced potential surge:

and the product of the winding turns (**N**) and the windings area (**A**) of the induction coil.

**The unit of magnetic induction (B) is the Tesla (T) = Vs/m2.**

The magnetic induction **B** and the field strength **H** are proportional to one another. The constant of proportionality is the magnetic field constant (**μ0**), given by experimental measurement.

In vacuum and also with sufficient accuracy for air, this leads to:

The magnetic induction (**B _{L}**) in air for the above example is then given by:

**Magnetic Flux F**

The magnetic flux (**F**) is the scalar product of the magnetic flux density (**B**) and the area vector (**dA**).

If (**B**) passes perpendicular through the area and the field is homogeneous:

The unit of magnetic flux (**F**) is the same as that of the voltage surge (Vs) (Voltsecond) or Weber (Wb).

**Faraday’s law**

Up until now we have considered static magnetic fields. If the magnetic flux changes with time, a voltage U is induced (Faraday’s law).

U = induced voltage

t = time

The polarity of the voltage is such that a current is generated on closing a circuit whose induced magnetic field opposes the original magnetic flux, i.e. it tends to reduce the magnetic field (Lenz’s rule – Figure 1.).

Taking a winding with N turns, Faraday’s law can be expressed in the following form.

**A** = cross section of the coil**l** = length of the coil or of the magnetic circuit**I **= current through the coil**L** = inductance of the coil [H(enry) = Vs/A]

So the inductance limits the change in current once a voltage is applied. It can be calculated from the coil data:

**A _{L}** = A

_{L}value; mostly in nH/N

^{2}

The energy stored in the magnetic field is subject to the following relationships:

The energy stored in the volume V is composed of both the magnetic field strength **H** and the magnet flux density **B**. For transformers and chokes with ferromagnetic cores, the flux density is limited by saturation and is constant throughout the magnetic circuit. If an air gap is introduced (material with permeability μ~1), the field strength is highest in this air gap with H = B/μ. It follows that the energy density is highest in the air gap. One also speaks of the energy being stored in the air gap.