From Home Inventions book (DK publisher), Matchbox microphone.
The graphite in the lead conducts electricity from the battery through its carbon atoms. Had a quick look up but think the graphite has a covalent bond which hold together in layers connecting 3 carbon electrons of a atom and so leaves a free carbon electron to move like the loose electron does in a copper atom. This is why it conducts.
The loose piece of lead from a pencil which lays across the two other lead sticks conducts but can move if you good it and so you get this break in circuit and change of current and sound of the air being blown as it rolls.
Had crocodile clip wires, split a pencil or two as they kept break and gaming too short to go across a matchbox. Was cool. Hooked up an affordable oscilloscope (jyetech d1... something) to visually see the sound and change in current.
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