Electricity and Magnetism > DC Circuits > RC Circuits
 DCS# 5F30.60
NEON RELAXATION OSCILLATOR
neon relaxation oscillator
APPARATUS
HP DC power supply 202-08-E
9 μF capacitor 202-19-E2
two 1.5 MΩ resistors 107-resistor cabinet
NE-32 neon bulb 202-19-E2
Simpson multimeter 107-01-H
video camera 202-09-D

DESCRIPTION
A neon bulb connected across the capacitor in an RC circuit flashes periodically.  The analog meter shows the rise and fall of the capacitor voltage.  The neon bulb lights at about 65 V and extinguishes at about 55 V.  One can vary the flash rate with a second identical resistor in parallel or series with the first.
 
NOTES

To show the waveform, use a voltage divider and storage scope to display the voltage across the bulb.  The laser power meter can be used to simultaneously monitor the brightness of the bulb.