Name: _________________________________________
Photoelectric effect Virtual Lab
Introduction:
The photoelectric effect, explained by Albert Einstein in the early years of modern physics, describes what happens when light
of certain frequencies strikes certain metals. The photoelectric effect is the principle evidence for light's particle nature and has
led to the development of many modern devices. In this investigation, you will learn the basic principles behind the
photoelectric effect.
Procedure:
• go to --> http://phet.colorado.edu/en/simulation/photoelectric and choose RUN NOW
• In the box titled TARGET, select sodium (if it is not already selected)
• Slide the wavelength dial (the one with the rainbow of color) all the way to the right (IR - 850 nm)
• Slide the intensity dial to 10%
• What happens? _________________________________________________________________________
• SLOWLY slide the WAVELENGTH dial to the left until you see electrons beginning to be ejected from the sodium surface.
• What wavelength gives you the first ejection of electrons? ________________
• Assuming the speed of light in a vacuum, calculate the frequency of this wavelength (1 nm = 10-9m; and c = λf)
_______________________________________________
• This is the threshold frequency for sodium.
• Now, increase the intensity to 50%
• What happens? __________________________________________________________________________
• With the intensity at 50%, move the wavelength dial back to the right into the RED range.
• What happens? __________________________________________________________________________
• Increase the intensity to 100%.
• What happens? __________________________________________________________________________
• Now, put the intensity back to 10% and slide the wavelength back to the threshold frequency for sodium.
• Note the velocity (i.e. kinetic energy) of the ejected electrons. Describe their kinetic energy
_______________________________________________________________________________________
• Now, slide the wavelength dial to 450 nm.
• What happened to the kinetic energy of the ejected electrons? ___________________________________
• Slide the intensity dial to 100% and describe what happens.
_____________________________________________________________________________________________________
_________________________________________________________________________________
• Move the wavelength all the way into the UV range and record your observations.
___________________________________________________________________________________________
• Repeat the above procedure for zinc and copper and answer the analysis questions below.
Analysis
1. What is the threshold frequency of each metal?
Sodium_________ Zinc ____________ Copper _______
2.
What happens if the frequency of light striking the metal is less than the threshold frequency of that metal?
3.
What do I need to do if I want to increase the AMOUNT of electrons being ejected from the metal?
4.
How do I increase the kinetic energy of the ejected electrons?
5.
Google "applications of the photoelectric effect" and list three things you use daily that are based on this physics principle.