NOTES ON EXPERIMENTS: Forced harmonic motion of a galvanometer

An experiment on forced simple harmonic motion can be carried out using suspended moving coil galvanometer driven by a very low frequency oscillator. This experiment uses a Gambrell galvanometer with a suspended mirror and coil of resistance 20 Ω at a distance of 96 cm from a traditional lamp and scale assembly. The galvanometer is driven by a Philip Harris S-range power signal generator whose output can be tuned over the frequency range from 0.7 Hz to 100 kHz and which is connected in series with a Telequipment D54 oscilloscope on the 50 mV cm^-1 range with the input switched to the DC position. This arrangement allows the amplitude and phase of the driving current to be monitored and at the same time the 1 MΩ input resistance of the oscilloscope limits the current through the galvanometer. Variable damping is achieved by changing the resistance R₁ of the resistance box in the range 500-10000 Ω. The tapping key serves to damp out galvanometer oscillations when required.