Magnetic Fields

This is the medium for energy conversion and transfer in electric machines and transformers.

Using magnetic fields we can make Magnetic Circuits

Magnetic Flux

$\varphi$: the number of lines of magnetic force passing through an area in space in Weber (Wb)

Magnetic Flux Density

B: magnetic flux density is flux per unit area $B=\frac{\varphi }{A}$ and its units are Tesla (T)

Magnetic Field Around a Current Carrying Wire

Right Hand Rule

The direction of flux follows the r.h.r when you point your thumb in the direction of current flow

and X means current goes “in” and a “dot” means the current is going out.

Intensity

Intuitively “effort by a current to cause a magnetic field”.
This is given by Amperes law:
This also the formula for MMF in Magnetic Circuits
${\int }_{}^{}H\cdot dl=I_{net}\Rightarrow Hl=NI\Rightarrow H=\frac{NI}{l}$
where l is the circumference of the circle in which H is acting and the units are Ampere-turns/m and the integral is a line integral

We can examine the magnetic field on electric magnets (Solenoids (Electromagnets))