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close this bookElectrical Machines - Basic vocational knowledge (Institut für Berufliche Entwicklung, 144 p.)
close this folder2. Basic principles
close this folder2.3. Force action of the magnetic field
View the document2.3.1. Force action on cur rent-carrying conductors
View the document2.3.2. Force action on current-carrying coils (motor principle)

2.3.1. Force action on cur rent-carrying conductors

Operating principle

A current-carrying conductor is enclosed by a magnetic field. If this conductor is entered into a magnetic field, the individual fields are superimposed.

Figure 17 - Force actions of current-carrying conductors in the magnetic field

(1) Basic presentation of the superimposing fields
(2) Force action of the superimposed fields
1 Force direction

On the one hand there is magnetic flow boosting. Conversely, one encounters magnetic flow fading.

A current-carrying conductor is pushed away from the external magnetic field towards the weaker field side.

Left hand rule (motor rule)

If the left hand is positioned thus in a magnetic field so that the field lines enter the palm of the hand and the projected four fingers are directed towards the conductor current, then the extended thumb points in force direction towards the conductor.

Figure 18 - Left-hand rule (motor rule)

1 Current direction in conductor
2 Direction of the magnetic field
3 Direction of movement

Electrodynamic law of force

Force is yielded through the following equation:

F = B · l · I · N




magnetic flow density of the external magnetic field


current in the conductor


conductor length in the magnetic field


number of conductors in series circuit (coils)