This year I used our magnificent induction coil that dates back to the 1880s or 1890s to create a little physics Christmas metal tree demo. The pointy tips are necessary to concentrate the charge.
The induction coil is like a step-up transformer and converts the 12 V input to more than 30 000V output. The breakdown voltage of dry air is 30 000V per cm and in the video the sparks are clearly 5 cm long or more. That is 150 000V are generated. A whiff of ozone can also be detected in the surrounding air.
I hope you enjoy it: My next idea is to place some copper chloride and a bit of ethanol in the metal dish and let the sparks ignite the flammable mixture to create green flames.
- Discharges
.
.
) for one of our open days, using an electric fly swatter as the source of sparks and hence electromagnetic waves and a receiver antenna and coherer (in my case, a plastic cup with aluminium tape on two sides as electrodes and filled with aluminium balls) with an LED in series. With each spark produced by the swatter, the LED would light up, but I had to reset it every time by gently tapping the cup, causing the balls to move slightly. 
