Modern Physics > Quantum Effects > Photoelectric Effect DCS# 7A10.15

PHOTOELECTRIC EFFECT WITH A NEON BULB


APPARATUS
 
neon bulb
202-13-A2
set of colored LEDs with batteries
202-21-G6
resistor
214-01-A
100 V DC power supply
202-08-E
momentary SPDT switch
101-09-D5


DESCRIPTION The power supply voltage applied to the neon bulb is just below the threshold necessary for the bulb to light, about 74 V.  Shining a green laser, a blue or uv LED on the bulb will cause it to glow, as electrons are ejected from the metal electrodes and the bulb becomes conducting, but a red laser and yellow LED will not.  The bulb extinction voltage is about 65 V, so the switch is used to open the circuit and extinguish the bulb between trials.
NOTES
The decade resistor should be set to 500 ohms.  The switch should be connected so that it the circuit is normally closed.
REFERENCE

The Physics Teacher 44, 310 (2006).