7A10.10 Photoelectric Effect

PURPOSE: To demonstrate the photoelectric effect to students.

DESCRIPTION: A zinc bar is attached to a gold-leaf electroscope. The electroscope is charged by making brief contact between a power supply and the zinc bar. Light from a small germicidal lamp is shone upon the zinc bar and the leaves of the electroscope fall. (The image of the electroscope is project on the wall by use of a carbon arc lamp and bench.)

SETUP TIME: Medium to Long

COMPONENT LIST:

    


  1. Zinc bar, germicidal lamp, sheet of glass          All in a box marked "Photoelectric effect" over by light sources
    2. 


  2. Optical bench and carbon arc lamp          Light Sources
    3. 


  3. Power Supply          On the counter with the other power supplies
    4. 


  4. Gold Leaf Electroscope          In Static Electricity cabinet


  5. Various cords          In cord storage

SUGGESTIONS: This is a great demonstration to do for students because it is something they usually only read about. Talk about the work function. Additionally, a sheet of glass (provided in the box) can be put between the germicidal lamp and the zinc plate to stop the UV photons from reaching the plate (which thereby stops the gold leaves from falling).

REFERENCES: PIRA 7A10.10

OTHER NOTES: Our gold leaf electroscope is starting to fail...be very careful when "charging" the electroscope and make sure the leaves do not fold over on themselves. Also, avoid looking at the germicidal lamp or holding it close to your eyes. (UV light causes cataracts.)