The induction coil is located in Set 4, Cabinet 2, Shelf 1. Explain to the students how the interrupter functions. Close the reversing switch in the primary circuit and show the spark that jumps between the needle point terminals of the secondary coil, an inch spark is sufficient. Connect the secondary coil terminals to the DC input terminals of the oscilloscope with 500,000 Ohms in series and 5000 Ohms shunting the scope terminals.
Polarity is of no consequence since the secondary coil is isolated.
With care you can synchronize with the fine control of the scope to the vibrator frequency. Operate the induction coil primary on about 8 V. Call attention to the high peak voltage developed in one direction and the quite low value developed in the opposite direction. If the current in the primary is reversed, the polarity of the peak developed in the secondary is reversed. This means that it is possible to have in the secondary circuit a unidirectional current if there is placed in the secondary circuit a small spark gap large enough to not pass the lower voltage but small enough to offer little opposition to the passage of the higher pulse. In practice the cotton insulation on the wire often serves the same purpose as the small gap.