7A10.35 - Photocells

Code Number:
7A10.35
Demo Title:
Photocells
Condition:
Good
Principle:
Planck's Constant
Area of Study:
Modern Physics
Equipment:
Photocells, Photocell Circuits, Mini Amplifier, Photocell Controlled Motor, Voltmeter.
Procedure:

Connect the photocell to the voltmeter and read resistance as a function of brightness shining on the photocell.

There are several battery powered photocells and photocell circuits that can be used for a variety of demonstrations.  

The photocell circuit on the small circuit board has a light that will glow brightly when under full illumination and will dim and eventually go out as the photocell is covered by a finger or a small film canister.

References:
  • Paul Gluck and Bernd Saering, "No Time Lag in the Photoelectric Effect", TPT, Vol. 48, #5, May 2010, p. 285.
  • David L. Mott, "A Simple Transistor Demonstration", TPT, Vol. 18, #6, Sept. 1980, p. 460, also A Potpourri of Physics Teaching Ideas - Electricity and Magnetism, p. 154.
  • R. L. T. Wolfson, "Intelligent Light Bulb A Negative Feedback Demonstration", AJP, Vol. 49, #4, Apr. 1981, p. 374. 
  • Forrest M. Mims III, "Solar-Powered Night Light", Electronic Sensor Circuits & Projects, p. 140.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.