Electrophorus

An electrophor is a form of historical Influence and serves for separation of electric charges and for producing high voltages by means of electrical induction. The name derives from the Greek elektron Elektrophor = amber ( as a prototype of the support of static electricity ) and pherein = wear off.

These and similar types of charge separation and the generation of an electric voltage were the basis of early research electricity in the 18th century, as it was largely run by Alessandro Volta. From 1775 it a useful Elektrophor was developed. The Göttingen scholar Georg Christoph Lichtenberg built in the same century large electrophoresis with up to 2.5 m in diameter, enabled the arcing over 70 centimeters.

Construction

An electrophorus consists of two parts: a metal plate having an insulated handle comparable to the plate of a capacitor, and a so-called "cake", which is electrically non-conductive and consists of a mixture of resin, sealing wax, and shellac. This cake is on a grounded metal base plate, as shown in the adjacent figure.

Manner of use

The rear grounded cake is rubbed with fur, was common to use a cat's fur. This creates static electricity on the cake in the form of excess negative charges. Substituting the electrically neutral metal plate on the plate, so the induction of the electric field causes a displacement of the cake charges of the charge carriers in the metal plate. On the side of the metal plate that faces towards the pie, there is an accumulation of positive charge carriers (or a lack of negatively charged electrons) on the opposite side of the metal plate to an accumulation of negative charge carriers. Now, if the metal plate is grounded while said overlay on the loaded cake on her side facing away from the cake, for example by being touched with the hand, the excess electrons can flow from this side of the plate. Overall, the metal plate is no longer electrically neutral. She wears an excess of positive charges are but in equilibrium with the fixed negative charges in the cake. Now, the ground connection from the surface of the metal plate by, for example the hand withdraws, and the metal plate is lifted only at its insulated handle of the pie, so an increasing electrical voltage builds up between the metal plate and the ground potential to with increasing distance. Their height can be adjusted according to the relationship:

Calculate earth - from the amount of charge and the capacitance of the system metal plate. Since there is no current flow and hence no change in the electric charge occurs, but at the same time reduces the capacity of the device by the lifting of the metal plate, the voltage must increase by the factor by which the electrical capacitance decreases. This allows very high voltages in the range of several kilovolts can be achieved. When approaching a grounded rod ( electrode ) to the raised metal plate it then because of the high voltages to a short spark, an electrical discharge. Due to the sparking distance can be easily found that the voltage with respect to ground is considerably higher than at the time when they rested on the cake. The whole process can be repeated as often because the charges stored in the cake itself not be derived ( "consumed" ).

The electrical energy which is released during the short spark discharge has been previously applied in particular by the mechanical working during the lifting of the metal plate against the force action of the electric field.

Applications of the principle

The principle of electrophorus can be equivalently realized by rubbing the capacitor with an externally generated DC voltage charges rather than the dielectric of the capacitor. This is especially variable capacitors are in the design of a variable capacitor: If this variable capacitor loaded at its maximum capacity to its nominal voltage, electrically separated from the voltage source, and then decreases the capacity of the rotary motion, there is an increase in the voltage between the plates, with the result an electrical flashover.

The condenser microphone utilizes the changes in the distance of a sound generated by the capacitor arrangement in order to produce a voltage change ( LF signal ) thereof. It needed to charge a bias. In the electret microphone, which works similarly, this charge is permanently in an electret, similar stored in the cake of Elektrophor, and need not be renewed.

And the band generator uses the principle of the electrophorus: influenzierende the charge is generated either by " frictional electricity " ( by picking up the band of insulating material on the lower dielectric roll ) or by spraying (peak discharge) to the ribbon of an external voltage source. Charges on the tape are then moved in the upward passage of the belt from the earth. A further development of the band generator is the Pelletron.