# photoelectric work function confusionWatch

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#1
ok, so the work function is a property of a metal's surface and is always the same ie doesnt change. the work function is the minimum energy needed for an electron in the surface of a metal to emit from the surface of the metal

ok i have 2 questions

• how do electrons in the metal have a range of kinetic energies up to a certain maximum value if they receive the same incident energy ( e =hf ) because if ke max = hf - work function and hf and work function are constant how does ke max vary
• if a photon or electron misses a free/delocalised electron in the surface of a metal and it hits an electron in one of of the positive ions, this electron can excite and if it has enough energy it can emit. this exact energy is not the work function because the work function is a property of the metal surface not of individual electrons, what is this minimum energy needed for electrons in shells to leave the outermost shell of the atom/ion called- excitation energy or something else
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5 years ago
#2
(Original post by JacobD96)
how do electrons in the metal have a range of kinetic energies up to a certain maximum value if they receive the same incident energy ( e =hf ) because if ke max = hf - work function and hf and work function are constant how does ke max vary
In this context, hf is the energy of the incident light striking the surface of the metal and is directly related to the wavelength. E=hf is therefore not a constant.

The work function is the energy needed to pull an electron away from its atom.

Therefore, kemax is the excess energy (difference) between the two.

That means if hf >= W then the electron will be ejected.

So kemax is determined by the incident E.

(Original post by JacobD96)
what is this minimum energy needed for electrons in shells to leave the outermost shell of the atom/ion called- excitation energy or something else
Electron binding energy.

(Excitation energy is used for electrons jumping to a higher shell.)
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5 years ago
#3
(Original post by JacobD96)
ok, so the work function is a property of a metal's surface and is always the same ie doesnt change. the work function is the minimum energy needed for an electron in the surface of a metal to emit from the surface of the metal

*how do electrons in the metal have a range of kinetic energies up to a certain maximum value if they receive the same incident energy ( e =hf ) because if ke max = hf - work function and hf and work function are constant how does ke max vary

The equation refers to the maximum possible ke of the electron, not to the energy of any particular electron. In the experiment, electrons are emitted with a range of energies up to a clear maximum limit. The electron gets all the "hf" energy from a photon when they collide. What then happens is the electron, depending where it was in the metal surface, loses some of this energy on its way out. When it emerges it has less than hf. Electrons emerge with a range of energies because they all start from different places in the metal. No electron can emerge with all the hf energy because it needs some energy to get out. The electrons nearest the surface and most loosely bound will have the maximum possible energy. Others will have less. The work function, for that metal, is the least amount of energy the electron will lose on its way out. Most electrons will lose more than that and emerge with less energy.
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