  Electrical Machines - Basic vocational knowledge (Institut f�r Berufliche Entwicklung, 144 p.)  2. Basic principles  2.2. Measurable variables of the magnetic field  2.2.1. Magnetomotive force 2.2.2. Magnetic flow 2.2.3. Magnetic flow density

### 2.2.1. Magnetomotive force

Magnetic fields are caused by electric currents.

Magnetomotive force signifies the existence of a magnetic field if the current flows through a conductor loop. Figure 15 - Stationary induction

(1) Current-carrying conductor loop
(2) Current-carrying coil
1 Current flow direction

The current “magnetomotives” the enclosed magnetic field lines. The magnetomotive force can be increased if the same current is conducted several times through the field lines (Cp. Fig. 15). This applies for a current-carrying coil with a number of turns equalling N:

Q = I · N

Formula sign Q
Unit: (Theta)
[Q] = 1A

### 2.2.2. Magnetic flow

Magnetic flow denotes the total number of field lines of a current-carrying coil or a magnet.

Formula sign F
Unit: weber
F = V · s = 1 volt-second

### 2.2.3. Magnetic flow density

Magnetic flow density denotes the magnetic flow which permeates a certain surface in a vertical direction. Figure 16 - Definition of magnetic flow density

1 Surface element, e.g. 1 cm2

A uniform magnetic field is: Formula sign B
Unit: tesla 