High voltage devices and electrostatics

High voltage refers to electrical potentials large enough to produce visible sparks, corona and arcs through air, and a range of machines exists to generate it for demonstration, research and industry. At such voltages air can be ionised and broken down, allowing dramatic discharges, so these devices are popular in science teaching while also demanding careful safety precautions because the energies involved can be dangerous.

Electrostatic machines build up high voltage by mechanically separating electric charge. The Van de Graaff generator uses a moving belt to carry charge to a large metal sphere, where it accumulates to hundreds of thousands of volts, producing long sparks and making hair stand on end. Older influence machines such as the Wimshurst machine use rotating insulating discs and metal sectors to separate charge by electrostatic induction, storing it in capacitors called Leyden jars until it discharges as a spark.

Other devices generate high voltage electronically or thermally. A Jacob's ladder applies a high voltage across two diverging electrodes; an arc strikes at the narrow gap at the bottom and rises as the heated air carries it upward, then restarts, giving a climbing ribbon of sparks. A flyback circuit, the principle once used to drive the cathode-ray tubes of televisions, uses a transformer in which the rapid collapse of magnetic field induces a very high voltage pulse. These methods illustrate the physics of electric fields, breakdown and discharge that underlie high-voltage engineering.

Frequently asked questions

How does a Van de Graaff generator work?

A moving belt carries electric charge to a large hollow metal sphere, where it accumulates to a very high voltage, eventually producing sparks or other electrostatic effects.

What makes the spark of a Jacob's ladder rise?

An arc forms at the narrow gap between two diverging electrodes; the hot ionised air rises and carries the arc upward until the gap grows too wide, when a new arc strikes at the bottom.

What is a flyback circuit?

It is a transformer circuit in which the sudden collapse of a magnetic field induces a high-voltage pulse, a method historically used to generate the high voltage for television picture tubes.