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Question: milikan experiment photoelectric effect

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pepe1964
#1
Jul14-09, 04:34 PM
P: 6
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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PhysicsDruid
#2
Jul17-09, 05:44 AM
P: 6
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
pepe1964
#3
Jul18-09, 04:24 AM
P: 6
Quote Quote by PhysicsDruid View Post
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
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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