Piezoelectric lightning rod

A high graphite content pencil has been used to draw the lines of this figure. When electrical leads from a piezoelectric crystal contact two of the pencil lines that are separated by a small gap, the electric field generated by squeezing the crystal provides a voltage that produces a spark that arcs across the gap. This experiment illustrates the use of a lightning rod, shown as the vertical line at the right of the figure. (General Atomics - Larry Woolf)