physics-physics-lab-5-the-photoelectric-effect-this-lab-will-investigate-the-photoelectric-effect

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Physics Lab 5
The photoelectric effect
This lab will investigate the photoelectric effect. The photoelectric effect is the emission
of electrons from a surface when illuminated with light of a certain frequency. The first
insight to understanding this phenomenon was presented in 1900 by Max Planck. His
formula, E = hf, related the energy of a photon to its frequency. Albert Einstein extended
this idea of quantized photonic energy to a stream of photons (electromagnetic radiation)
and explained the photoelectric effect.
This virtual experiment is a Java Applet. Applets require the JVM (Java Virtual Machine).
It is not uncommon for the JVM to be outdated or not installed on a computer system,
causing the applet to fail to run properly if it runs at all. In that case you should download
(for free) and install the latest version from
http://java.com/en/download/manual.jsp
Some network administrators block Applets. In that case, contact your network
administrator or try a different Internet access point.
Instructions:

1. Go to http://phet.colorado.edu/sims/photoelectric/photoelectric_en.jnlp
2. Increase the intensity to 50%. You should notice the ejection of elections from the
surface.
3. Slowly increase the wavelength (λ) of the light until electrons are no longer ejected
and record the wavelength (λ) in the table below.
4. Calculate the frequency (f) for that wavelength and record it in the table below.
Remember that c=λf, where c is the speed of light (3 * 10^8 m/s).
5. Calculate the Energy (E) in joules for that wavelength and record it in the table
below. Remember that E = hf, where h the Planck constant (6.6 *10^-34 j*s)
6. Complete the Energy (E) in electro-volt (ev) and record it in the table below.
1 electron-volt (eV) = 1.6 X 10-19 J
7. Repeat the above step for each of the metals under the pull down menu.
Wavelength λ
Frequency f
Energy E
Energy
Metal
(nm)
(Hz)
(J)
(eV)
Sodium
541nm
Zinc
290nm
Copper
270nm
Platinum
200nm
Calcium
430nm

8. The minimum frequency of a photon that can eject an electron from a surface is
called the threshold frequency, ft. What is the threshold frequency, ft, for each of the
metals?
HINT: revisit instructions 3 & 4.
Metal

Threshold Frequency ft
(Hz)

Sodium
Zinc
Copper
Platinum
Calcium

9. The minimum amount of energy required for an electron to escape from a metal is
called the work function (W) and is given by the equation W = hft. What is the work
function for each of the metals in joules and electron-volts? HINT: revisit instructions
3 to 6.
Metal

Work Function E
(J)

Work Function E
(eV)

Sodium
Zinc
Copper
Platinum
Platinum
Calcium
10. Make the following additional adjustments to the simulation.
· Check the box “current vs. light intensity”.
· Check the box “electron energy vs. frequency”
· Select the Sodium.
· Use violet light (about 400 nm).
· Vary the intensity of the light and observe any changes in the number of
ejected electrons.
· Vary the intensity of the light and observe any changes in the number of
ejected electrons.
11. What’s the relationship between the intensity of the incident light and the number of
the ejected electrons?
12. What’s the relationship between the intensity of the incident light and the energy of
the ejected electrons?

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