Magnetic Induction, Magnetic Flux and Faraday’s Law
- Posted by doEEEt Media Group
- On October 28, 2022
In vacuum and also with sufficient accuracy for air, this leads to:
The magnetic induction (BL) 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).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).
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:AL = AL value; mostly in nH/N2
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.