2.5  Direction of movement of an arc

2.5.1  Heated air moves upwards

An burning arc normally moves. At a classical Jacob's ladder the movement is upwards. The common explanation for this fact is that heated air is moving upwards and given that an electric arc burns at 5000K - 16000K (cp. Figure 2.2 it will move upwards.

But there are also other causes of the movement.:

2.5.2  Relative speed of the electrodes

The points at the electrodes where the arc-plasma burns is although heated and at these points electrons and ions are emitted (thermionic emission). These points move relatively slow and slow down the velocity of the arc relative to the electrodes.

2.5.3  Magnetic Force

The higher the current, the higher is the influence of the magnetic force. An electric current consists of moving charge carrier. If a charge is moved relative to a magnetic field, a force is taking effect on the charge, known as Lorenz-Force. Figure 2.5 (a) illustrates the directions of the vectors.

This force leads to the phenomenon, shown in Figure 2.5 (b), that a loose on two conductors lying pole will move away from the source. This also happens to an arc: A force affects the arc to maximise the area enclosed by the electrical circuit.

Figure 2.5: Current, force and magnetic field

This page is part of a Frameset: Electrodynamic Sculpture: A Thesis by Rafael Bräg.