EMF generated by phototube using halogen light source.

EMF generated by phototube using halogen light source. White light from a Halogen lamp is sent into a CsAr photocell and the generated voltage (or EMF) is displayed on a screen via a projection voltmeter. See Fig. 1. The photoelectric cell in this demo has a thin layer of cesium deposited on the inside of the soda glass envelope, except for the clear part where light is allowed to enter. The gas inside the tube is inert argon. When visible light hits the cesium, there is a flow of photoelectrons from the cesium into the argon. The cesium becomes more positive as electrons leave. The argon becomes more negative, as does the central electrode which is bathed in the argon. Thus, there is a small potential difference between the two photocell electrodes which can be measured with a high input impedance voltmeter.