Northwestern Physics Demos                                 Go back to ATOMICS
DCS# 7A10.10NWU#  A-3Location:  various
title: Photo-Electric Effect
aka: Zinc or lead exposed to UV light

A freshly sanded zinc plate is placed on an electroscope and charged both positively and negatively.   The plate is illuminated with UV light.  The negatively charged plate discharges, unless a glass filter is placed in front of the UV light.   The positvely charged plate does not discharge.

    Explain why the positive plate does not discharge.
overall set up