iLab at Iona Prep

In the photoelectric effect, light hits a metal. Under certain conditions, the metal will eject electrons. The conditions caused an uproar in the physics community because experimental results did not agree with the current theory. When experiment does not agree with theory, then the theory needs to change. Albert Einstein won the Nobel prize for his explanation of the mechanism of the photoelectric effect.

What you see: On the left is a light source peeking through a grey metal electrode. You can control the wavelength of the light by clicking on the arrows. In the center you can control the brightness of the light by clicking on the arrows. On the right, you can control the voltage on the power supply by clicking on the arrows. Finally, you can change which metal is at the right by clicking on the metal. There is also on the left a count of the # Electrons Detected by the electrode and also the time of collection. NOTE: Changing any variable will clear the counter and reset the clock.

1. The first setup: (Set it up this way, if it is not already. Wavelength 500 nm; brightness 60; voltage 0.5 volts; metal Potassium. What you see: photons go from left to right. They cause electrons (dots) to be ejected from the metal, however the voltage causes them to be attracted back to the Potassium. None reach the electrode on the left. (A) decrease the voltage and you will see some electrons will reach the electrode on the left, and they will register as # Electrons detected.

2. Your teacher will tell you what measurements to make and what questions to answer.