modern_physics.gif (14139 bytes)

PHOTOELECTRIC EFFECT

(Not done as we do not have the equipment.)




EQUIPMENT
    redball.gif (326 bytes) Mercury Vapor Lamp (has been lost)
    redball.gif (326 bytes) Zinc Plate Electroscope
    redball.gif (326 bytes) Window Glass Pane
    redball.gif (326 bytes) Fur
    redball.gif (326 bytes) Ebonite Rod



NARRATIVE
            Certain metals emit electrons when illuminated by electromagnetic radiation of a particular wavelength. Zinc emits electrons when illuminated with ultraviolet light.Connect the mercury vapor lamp to 110 VDC and turn the switch on. To strike an arc, lift and release the round wire handle which is located in top of the shade. Allow about 2 minutes for warm up.Clean one side of the zinc plate with emery cloth or Carborundum abrasive. Connect the plate to the electroscope by means of the attached wire. (Be sure the plate is not grounded.) Place the clean face of the zinc plate in the ultraviolet light. Insert a pane of window glass between the UV light and the zinc plate to block the UV light. Charge the electroscope with a negative charge using the ebonite rod. (The shadow of the electroscope may be projected for easier viewing.) Remove the glass plate and the electroscope will be discharged indicating that the electrons are leaving the zinc plate.