Sparks

Spark is a fascinating physical phenomenon that occurs in nature e.g. as lightning. We used the Wimhurst induction generator as a source of high voltage for our experiments as it easily provides many tens of kilovolts. If the electric field intensity in air exceeds a certain value, the ions are accelerated to such a speed that they are able to ionize other molecules. This causes an avalanche creation of new ions and a conductive channel is formed that discharged the charge. The air is heated to a high temperature, expands rapidly and collapses again, which causes the typical sound and light. Another form of the spark is a brush discharge that can be seen in the first picture of the second row. In the pictures in the third and fourth rows one can see a discharge between aluminium foil pieces fixed on a insulating plate. By a long exposition we achieved that there are more sparks in most pictures. The last three pictures show spark spectrum observed using a diffraction grating. The spectrum has distinct lines that are caused by the quantized energy levels of the radiating gas.