Hi please help me I have a test tomorrow worth 30% and I cant even work out the most basic of questions because my book assumes prior physics and knowing constants etc which I dont know!(adsbygoogle = window.adsbygoogle || []).push({});

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 havent found anything under the photoelectric section converting KE to speed, I asked my friend and he saidKE = (1/2)m*v^2which 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 thats correct but please correct me if Im 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 is9.109*10^-31 kg

I've also tried an equation I found on the internet:

V^2/C^2 = (2*Kmax)/mc^2and 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!

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# Homework Help: Speed of fastest electron w\ workfunction & photon energy

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