- #1
fredwacko40
- 3
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Hi please help me I have a test tomorrow worth 30% and I can't even work out the most basic of questions because my book assumes prior physics and knowing constants etc which I don't know!
The work function of tungsten is 4.50 eV. Calculate the speed of the fastest electrons ejected from a tungsten surface when light whose photon energy is 5.80 eV shines on the surface.
Ok so I've read all the theory and I haven't found anything under the photoelectric section converting KE to speed, I asked my friend and he said KE = (1/2)m*v^2 which didnt work. So far I have
hf = Kmax + (I) where (I) is that funny I in a O symbol
5.8 = Kmax + 4.5
Kmax = 1.3
Im assuming that's correct but please correct me if I am wrong, so I now have the max Kinetic energy but no way to convert it to speed. The back of the book says the mass of an electron is 9.109*10^-31 kg
I've also tried an equation I found on the internet:
V^2/C^2 = (2*Kmax)/mc^2 and after a little searching I found c to be the speed of light, but that returned a value of V = 68.81 which although a nice number wasnt right, 676 km/s is meant to be the answer, perhaps I just have to convert it? I think its in m/s atm though so that would make it 0.06881 km/s? That would be way off... please help me! I need to pass this test!
The work function of tungsten is 4.50 eV. Calculate the speed of the fastest electrons ejected from a tungsten surface when light whose photon energy is 5.80 eV shines on the surface.
Ok so I've read all the theory and I haven't found anything under the photoelectric section converting KE to speed, I asked my friend and he said KE = (1/2)m*v^2 which didnt work. So far I have
hf = Kmax + (I) where (I) is that funny I in a O symbol
5.8 = Kmax + 4.5
Kmax = 1.3
Im assuming that's correct but please correct me if I am wrong, so I now have the max Kinetic energy but no way to convert it to speed. The back of the book says the mass of an electron is 9.109*10^-31 kg
I've also tried an equation I found on the internet:
V^2/C^2 = (2*Kmax)/mc^2 and after a little searching I found c to be the speed of light, but that returned a value of V = 68.81 which although a nice number wasnt right, 676 km/s is meant to be the answer, perhaps I just have to convert it? I think its in m/s atm though so that would make it 0.06881 km/s? That would be way off... please help me! I need to pass this test!