Model of semiconductor.
Electric current board and nail model with timer.
About 100 nails are driven randomly into a board. The drift velocity is proportional to the square root of the field, so that only a modified "Ohm's law" applies. In this case, the apparatus simulates the motion of charge carriers in semiconductors under the action of an electric field. The field is increased by changing the tilt of the board.
Meiners, Physics Demonstrations Expts., 40-1.1 Charge Motion Demonstrator, 1220.