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Vanessa Reyes_4C wrote:For problem 1.69b do you have to convert electron volts to joules, and then use the E=hc/frequency equation?
Yes, you have to make sure all your SI units are correct before doing the problem.
1eV=1.602 x 10^-19 J
I think that the work function depends on the problem, the equation with the work function is Kinetic Energy = hv - work function, so if you have the other values you can compute it that way, but I think otherwise some number for the work equation needs to be given in the problem. If that is the case, should we memorize the number to convert electronvolts to joules?
In metals, free electrons may float about the metal but do not have enough energy to escape from the surface. When additional energy is added in the form of a photon that reaches the threshold energy, these free electrons can escape from the surface of the metal and be emitted
Brice McKeown 3D wrote:Also, I am a little confused on what it means when the electron is ejected from the metal. Like is it light? Like what is the purpose of the electron being ejected?
It has to do with the experiment we discussed in class where light (photons) hit a block of metal, leading to the e- being ejected. The main takeaway from the experiment was that light has particle properties, not only wave-like properties, meaning a larger wavelength will not mean more e- are ejected. The work function equation that people are discussing above can be used to calculate how much energy is needed from the photon to eject an electron from a specific metal.
If the energy of the light (photons) is higher than the work function (the little symbol that looks kind of like the green lantern symbol) then its met the "threshold" and can eject an electron. The difference between the work function (threshold) and the energy from the light equates to what the kinetic energy of the electron being ejected will be. It doesnt really happen but if the energy from the light is equal to the work function then the electron would be ejected but with a kinetic energy of 0.
In most of the problems I've seen, they don't usually give a number as the work function outright. Generally it's referred to as "the energy required to remove an electron from _____ surface" or whatever. I've also seen problems where the frequency or wavelength is given rather than the energy and you just use the equations to figure out the work function from there.
Work function is essentially the energy required to eject an electron. The equation of the work function is work function = h* Vo ( with Vo being the minimum frequency needed to eject an electron). Sometimes work function us given in eV so make sure to covert eV into Joules to avoid unit confusions.
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