Fig. 43.
Ruhmkorff Coil.
Fig. 44 shows a diagram of a Ruhmkorff coil, the letters referring as follows:
C the iron core, P the primary coil wires, I the insulating tube between primary P and the secondary coil S. In small coils this may be dispensed with, and a heavy layer of paraffin wax laid over the primary coil. D D are the ends of the secondary, showing sparking taking place between a pair of balls (or between the electrodes of a gas burner); R is a stiff spring fastened to the coil base and carrying a soft iron hammer, which is attracted toward the iron core, C, when current passes through the primary coil and magnetizes it. L is a battery, J, a condenser, to be more fully described later on. When the spring R touches the adjustment screw A at B, as they are insulated from each other, contact is made and reference to circuit will show that the current from battery L flows through primary coil, magnetizing the core and attracting soft iron hammer on R. As this bends forward, it breaks contact at B, the core loses its magnetism and the spring flies back, to again make contact. This is repeated many times per second.
Fig. 44.
As a heavy spark occurs at B on the break of contact, the condenser, J, is attached at M K. This is a series of insulated tinfoil sheets, which has the property of nullifying the spark at B, and so preventing the waste of platinum with which both adjustment screw A and spring R are equipped.
A Ruhmkorff coil differs from a simple primary coil in three main points. Two separate coils instead of one; high insulation, and a primary coil of few turns. In the simple coil we desired self-induction; here, we desire to avoid it as much as possible.