# Magnetic Induction, Magnetic Flux and Faraday’s Law

- Posted by doEEEt Media Group
- On October 28, 2022
- 0

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

The magnetic induction (**B _{L}**) in the 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**).

**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 voltaget = 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**= A

_{L}_{L}value; mostly in nH/N

^{2}

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

The energy stored in volume V is composed of magnetic field strength **H** and the magnetic 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.

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