Two simple electricity and magnetism lecture demonstrations: resonance in LC circuit and Ampere's law

Teaching these fundamental physical phenomena requires lecture demonstration accessible even for secondary school students. While there is a lack of such tools on the market, we design our own demonstrations.

1. We use an LC circuit to control brightness of an incandescent light bulb by tuning it in and out of the 60 Hz power grid resonance. The inductor is wound on standard 1-inch PVC pipe, it has 7000 turns of 18 gauge magnet wire; the length of coil is 0.7 m; the inductance is tuned with an iron rod. A bank of capacitors and switches allows to tune capacitance from zero to 48 uF with 2 uF increment. Q-factor of the resonance depends on the power of the light bulb used.

2. Ampere's law we demonstrate by running current from a motorcycle battery through two parallel wires suspended in a specially designed low-friction hinges. Depending on the direction of the current, the wires either attract or repel each other.

Both instruments can be easily reproduced in a school machine shop. More information is available upon request.