Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: eq123 on May 12, 2010, 10:12:25 AM
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i've been trying to figure out this problem..
The longest wavelength of light that causes electrons to be ejected from the surface of a copper plate is 243 nm. What is the maximum velocity of the electrons ejected when light of wavelength 200. nm shines on a copper plate?
the answer is 6.22 × 10^5 m/s
any ideas?
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You have asked the same question at physicalforums and you were already given several hints - have you tried to use them?
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You have asked the same question at physicalforums and you were already given several hints - have you tried to use them?
Spotted! ;D
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thank you for nothing!
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What equations do you know that may be relevant (perhaps look for Photoelectric effect, or similar)
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you could work that out using De Broglie's postulate - All matter has an associated wavelength, and the wavelength is inversely proportional to the mass x velocity.
in brief, Lambda = (Planks const)/(mass x veloc.)
Wiki it.
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I think this problem is related to the photoelectric effect.
"The longest wavelength of light that causes electrons to be ejected from the surface of a copper plate is 243 nm. What is the maximum velocity of the electrons ejected when light of wavelength 200. nm shines on a copper plate?"
Here the wavelength of 243nm indicates the minimum frequency of light required for the electrons to be emitted from copper plate. frequency = the speed of light/wavelength. Energy = Plank constant x frequency
Therefore, the maximum KE = the energy of the 200nm wave - work function(which equals to the energy of 243 nm wave).
From the maximum KE, you can determine the velocity.