[manarth]

My secondary school physics teacher was somewhat accommodating to "interesting" experiments - those which might look cool to teenagers whilst also providing a lesson in physics.

One of those was attaching electrical probes to each end of a pencil, and applying an electrical current. Graphite conducts extremely well: the pencil "lead" (actually graphite) heats up, glowing a bright orange colour, whilst setting fire to the wooden pencil surrounds. If you snap the graphite "lead", you can touch the two ends together causing a bright electrical arc.

It's a great physics demonstration, and graphite conductivity is the reason pencils aren't used in zero-gravity environments.