Demonstrates: By varying the electric field (by manipulating the potential across region of interest), electrons that would otherwise have enough energy to cross the gap are no longer able to.
Description: An old phototube attached to a circuit.
Instructions: When light of the right frequency is shone on the cathode, a current will be generated in the circuit. This can be measured using the picoammeter.
Connect one plug to the picoammeter, and another back into the case.
Shine light onto cathode.
Adjust settings on ammeter to show the current.
For stopping potential:
Connect a power supply (backwards), one to the diode, the other to the plug on the ammeter.
Follow the above steps for showing the current.
While current is running, adjust voltage on power supply.
Upon reaching a particular voltage, the current will stop.
Items Used: Phototube, picoammeter, laser pointer, power supply, camera (to project for class).
Notes:Math Description:
Size: Condition: Good. Hazard: Avoid shining laser at anyone.
