Download At what intensity is the laser set?

(VCL) Assignment - Photoelectric Effect
Experiment
Introduction
Though Einstein is most famous for his work in describing relativity in mechanics, his
Nobel Prize was for understanding a very simple experiment. It was long understood that
if you directed light of a certain wavelength at a piece of metal, it would emit electrons.
In classical theory, the energy of light was thought to be based on its intensity and not its
frequency. However, the results of the photoelectric effect contradicted classical theory.
These inconsistencies lead Einstein to suggest that we need to think of light as being
composed of particles and not just as waves. You will have a chance to recreate some of
the measurements that led to Einstein’s theory.
Procedure / Observations
1. Enter the Quantum Lab in VCL.
2. Set up the optics table for this experiment by selecting Photoelectric Effect (1) on the
clipboard (in the stockroom).
What source is used in this experiment and
what does it do?
At what intensity is the laser set?
At what wavelength is the laser set?
Which metal foil is used in this experiment?
What detector is used in this experiment
and what does it measure?
What does the signal on the phosphor
screen indicate about the laser light
shining on the Na foil?
3. Decrease the laser power to 1 photon/second.
How does the signal change?
4. Increase the power to 1kW.
How does the signal change?
5. Change the power back to 1 nW. Now increase the wavelength to 650 nm.
What do you observe?
Does the frequency of light increase or
decrease as wavelength is increased?
Does a lower frequency correspond to a
lower or higher energy?
6. Change the laser power to determine whether you can get the signal back to what it
was beford.
Can you get the signal back?
What is the difference between wavelength
and intensity?
Discussion