## What is Threshold Energy?

$c=\lambda v$

Jessica Luong 3E
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Joined: Sat Aug 17, 2019 12:17 am

### What is Threshold Energy?

Can someone re-explain to me what a threshold energy is? What do we need to know this for? Thank you!

Ian Morris 3C
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Joined: Wed Sep 18, 2019 12:18 am

### Re: What is Threshold Energy?

If I remember correctly, Threshold Energy is the minimum amount of energy needed to eject electrons from the surface.

Ashley Wang 4G
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Joined: Wed Sep 11, 2019 12:16 am

### Re: What is Threshold Energy?

The threshold energy is the energy (corresponding to a certain wavelength/frequency of light) needed to remove an electron from a metal surface when you shine light on it. If the energy of the light doesn't reach the threshold, the electron is excited but not ejected from the surface, no matter the intensity of the light. We need to know this (in the context of the problem) when solving questions about energy of a photon, energy of the ejected electron, etc. :)

Annika Zhang 1F
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Joined: Sat Jul 20, 2019 12:15 am

### Re: What is Threshold Energy?

Threshold energy is the lowest possible amount of kinetic energy needed to collied and eject electrons.

Diana A 2L
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### Re: What is Threshold Energy?

Do ionization energy and threshold energy have the same numerical values? And what is the difference between the two?

Posts: 52
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### Re: What is Threshold Energy?

Ionization energy refers to the energy needed to remove an electron from a gas, vs. threshold energy for a solid.

EricZhao3G
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Joined: Tue Oct 08, 2019 12:16 am

### Re: What is Threshold Energy?

Threshold energy is the least amount of energy needed to eject an electron off of a surface. Threshold energy is important when using Einstein's photoelectric equation since it is one of the three components of his equation: E(photon) - E(threshold) = E(kinetic).

Keerthana Sivathasan 2E
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### Re: What is Threshold Energy?

Threshold energy is the work function. We need to know this because it's different for each metal surface, and you have to know what the minimum energy required to make an electron fire off the surface would be. Another thing to note is that the number of electrons emitted of the metal surface depends on the intensity not frequency of the light, however, kinetic energy of the electrons does depend on the frequency of the incident light.

Osvaldo SanchezF -1H
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Joined: Wed Sep 18, 2019 12:21 am

### Re: What is Threshold Energy?

The threshold of energy is the minimum amount of energy need to eject an electron which corresponds to a wavelength of 683 nm if I remember correctly. You can deduce the energy used by using one of the equations that he gave to see if there is enough energy to even Emit an electron.

Pipiena Malafu 3J
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Joined: Fri Sep 28, 2018 12:27 am

### Re: What is Threshold Energy?

As part of the photo electronic effect, light below a certain threshold frequency, no matter how intense, will not cause any electrons to be emitted. Light above the threshold frequency, even if it's not very intense, will always cause electrons to be emitted.

This site might be resourceful: http://physics.bu.edu/~duffy/PY106/Phot ... ffect.html