Question: milikan experiment photoelectric effect

In summary, the treshold frequency of the incident light for an electron of the cathode to be ejected is -in this particular experiment- 43.9 *10^13 Hz. This corresponds to an energy of E=hf = 43.9 * 10^13 s-1 * 4.136*10^-15 eV s = 1.82 eV.
  • #1
pepe1964
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Hi, I'm a newbie starting to study physics at a later age (45).
I've tried to find an answer to my question in this forum, the internet , books, etc... already.

I'm reading Modern Physics, Tipler & LLewelyn. On p. 139 he presents a diagram illustrating Millikans experiment on work function (photoelectric effect). I've seen this same diagram on numerous other physics websites.
(eg. http://hyperphysics.phy-astr.gsu.edu/hbase/mod2.html#c3"

The treshold frequency of the incident light for an electron of the cathode to be ejected is -in this particular experiment- 43.9 *10^13 Hz.
Now, this corresponds to an energy of E=hf = 43.9 * 10^13 s-1 * 4.136*10^-15 eV s = 1.82 eV

Now my question: which element (metal) was this? Which material has a work function of 1.82 eV? I can't find any.

Am I messing up on this? I'm really stuck. Can someone bring some clarity?
 
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  • #2
I believe it was sodium (Na). However, experiments constantly refine our knowledge of materials (take AMO and Condensed Matter fields for example). Sometimes you will find Na quoted at 1.82, then higher as you found. Take this paper from the 70s for example. The research showed a jump from at the time 2.25 to 2.75 for the Na work function. As experimental devices become more precise, so does our data. I'm not an expert on this particular experiment (I wasn't around then), but hopefully this helps.:

http://prola.aps.org/pagegif/PRL/v26/i7/p380_1/p381 [Broken]
 
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  • #3
PhysicsDruid said:
I believe it was sodium (Na). However, experiments constantly refine our knowledge of materials (take AMO and Condensed Matter fields for example). Sometimes you will find Na quoted at 1.82, then higher as you found. Take this paper from the 70s for example. The research showed a jump from at the time 2.25 to 2.75 for the Na work function. As experimental devices become more precise, so does our data. I'm not an expert on this particular experiment (I wasn't around then), but hopefully this helps.:

http://prola.aps.org/pagegif/PRL/v26/i7/p380_1/p381 [Broken]

Many thanks Physicsdruid,
The link requires authorization however. Is there a way to send me the article as such?

After the many replies to my question (in the homework section), I began to have doubts again: the 1.82 is much LOWER than any other data available. If the metal surface was unpure (or whatever bias), the value should have been at least HIGHER than the modern data available...
Thanks again.
 
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1. What is the Milikan experiment?

The Milikan experiment, also known as the oil drop experiment, was conducted by physicist Robert A. Millikan in 1909 to measure the fundamental unit of electric charge, known as the electron charge.

2. What is the photoelectric effect?

The photoelectric effect is the phenomenon where electrons are emitted from a material when it is exposed to light of a certain frequency. This effect was first observed by Heinrich Hertz in 1887 and was later explained by Albert Einstein in 1905.

3. How did the Milikan experiment contribute to our understanding of the photoelectric effect?

The Milikan experiment provided accurate measurements of the electron charge and helped to confirm Einstein's theory that the energy of a photon is directly proportional to its frequency. This experiment also showed that the photoelectric effect is only dependent on the frequency of the incident light, not its intensity.

4. What was the setup of the Milikan experiment?

The Milikan experiment involved suspending tiny oil droplets in an electric field between two parallel plates. The droplets were then exposed to a beam of X-rays, causing them to become electrically charged. By measuring the rate at which the droplets fell or rose in the electric field, Millikan was able to calculate the charge of each droplet and therefore determine the value of the electron charge.

5. How did the Milikan experiment impact the field of physics?

The Milikan experiment was a groundbreaking experiment that provided accurate measurements of the electron charge and confirmed important theories about the nature of light and matter. This experiment paved the way for further research and advancements in the field of quantum mechanics and solidified the idea that light has both wave-like and particle-like properties.

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