The Motor Principle
When a conductor carrying a current is in an external magnetic field perpendicular to the conductor, a force perpendicular to the conductor and the external magnetic field will be exerted on the conductor. (I know this sounds confusing, hopefully the third picture can clear things up a bit.)
The direction of the force on the conductor can be described by the right-hand rule.
1. With the right hand, the thumb points in the direction of the current.
2. The fingers point in the direction of the external magnetic field.
3. The resulting force exerted on the conductor will go outwards of the palm.
The definition of the ampere is described with the motor principle. One ampere is defined as the amount of current, which produces a force of 2 X 10-7 newtons per metre of conductor when it flows through two straight parallel conductors a metre apart in a vaccum.
Examples of electric devices that operate on the motor principle are analog electric meters such as voltmeters, ammeters and galvanometers. In the case of MagLevs, important applications of the motor principle include an electric motor and the train. An electric motor consists of a permanent magnet (stator) which produces an external magnetic field and a conductor coiled to form an electromagnet as the armature (rotor) which is free to rotate within the external magnetic field. The armature is connected to a voltage source through brushes and a commutator, while the rotor in a Transrapid MagLev is directly wired to the train because the rotor doesn't move in relation to the train.
The speed of a motor's rotation depends on the strength of the external magnetic field from the permanent magnet and the armature's electromagnetic field strength, which is determined by the number of coils, the amount of current flowing through it and its magnetic permeability and the load to the shaft. Note, when the conductor of a motor is not supplied with a current and when the shaft is moved by an external force, a current will flow out from the conductor. This is the effect of an electric generator. It's because a current is induced when the rotor is moved inside the magnetic field of the stator. A MagLev uses the same principle for charging up its onboard batteries. That is, the cable windings moving in a magnetic field induce a current for the onboard batteries.
The Propulsion System of the Transrapid operates on the motor principle similar
to that of an electric motor.
Basically, a motor is divided into two halves, one half (the electromagnetic stator)
in the guideway and the other half (the
rotor) in the train's undercarriage. Instead of a motor using an electromagnetic
rotating field, the Transrapid system uses an electromagnetic travelling
field, which propels the train forward or brakes the train to a stop when
the direction of the electromagnetic field is reversed.
Want more side info on MagLevs? Then let's take a look at the pros and cons of MagLevs.