# Voltage question (photoelectric effect)

• Physicsissuef
In summary: I think it has something to do with the quantum mechanical behavior of electrons. They have more energy when they're 'excited' and that's what makes them 'max' kinetic energy.
Physicsissuef
I learn about photoelectric effect. Can somebody tell me why:
$$eU_z=E_k_,_m_a_x$$
What is $$eU_z$$?

Also I found this,
On cranking up the negative voltage on the collector plate until the current just stops, that is, to Vstop, the highest kinetic energy electrons must have had energy eVstop on leaving the cathode. Thus,

eVstop = hf - W

Well, semiconductive materials tend to have a 'work function' which is basically the energy difference between, I believe, the conduction and valence bands in the atom. This corresponds to a certain voltage needed simply to free the electron from the atom (and give it a Kinetic Energy + Potential Energy = 0); any additional energy will go into accelerating the freed electron. Due to conservation of energy, the kinetic energy of the electron can only correspond to the remaining voltage defined by (voltage in - band gap voltage). I think this is called 'maximum' because in reality electrons aren't really the classical type of objects and you have to think in terms of statistics and not concrete principles. That is to say that the electrons need not absorb all that energy available (and hence have a lower KE than the maximum available).

dst said:
Well, semiconductive materials tend to have a 'work function' which is basically the energy difference between, I believe, the conduction and valence bands in the atom. This corresponds to a certain voltage needed simply to free the electron from the atom (and give it a Kinetic Energy + Potential Energy = 0); any additional energy will go into accelerating the freed electron. Due to conservation of energy, the kinetic energy of the electron can only correspond to the remaining voltage defined by (voltage in - band gap voltage). I think this is called 'maximum' because in reality electrons aren't really the classical type of objects and you have to think in terms of statistics and not concrete principles. That is to say that the electrons need not absorb all that energy available (and hence have a lower KE than the maximum available).

Please note that the standard photoelectric effect experiment is done on metals, not semiconductors, which would have added a different level of complexity. So the question between the conduction and valence band isn't valid here within this scenario.

Zz.

## 1. What is voltage in relation to the photoelectric effect?

Voltage refers to the difference in electric potential between two points. In the photoelectric effect, voltage is used to describe the amount of energy needed to eject an electron from a metal surface.

## 2. How does voltage affect the photoelectric effect?

Voltage directly affects the energy of the ejected electrons in the photoelectric effect. Increasing the voltage increases the energy of the electrons, resulting in a higher kinetic energy and faster speeds.

## 3. What is the minimum voltage required for the photoelectric effect to occur?

The minimum voltage required for the photoelectric effect to occur is known as the threshold voltage. This voltage is dependent on the type of metal used and the frequency of the incident light.

## 4. Can voltage be used to control the intensity of the photoelectric effect?

Yes, voltage can be used to control the intensity of the photoelectric effect. By varying the voltage, the energy of the ejected electrons can be adjusted, which in turn affects the number of electrons ejected per unit time.

## 5. How is voltage related to the stopping potential in the photoelectric effect?

Voltage is directly related to the stopping potential in the photoelectric effect. The stopping potential is the minimum voltage needed to stop electrons from reaching the collector plate. It is equal to the maximum kinetic energy of the electrons, which is dependent on the incident light frequency and the work function of the metal.

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