# Calculating Longest Wavelength of Light to Eject Electrons

• chemilliterate
In summary, a student is seeking help with a question on quantum mechanics in a chemistry course. They need to calculate the longest wavelength of light that can eject electrons from a surface, given a certain energy requirement. Another user explains that light comes in packets and the energy of the packet depends on its frequency. The student expresses gratitude and another user suggests checking out online courses for a better understanding of quantum mechanics.
chemilliterate

I posted this in the Quantum Physics forum as well, but I ran across this one and thought it may help to put it here too. Sorry for the double post.

Hi everyone... I am new to this site. I am currently taking a major-related Chemistry course that is concentrating on quantum mechanics right now. I have been working on a homework question for about an hour now, and I am no closer to figuring it out than when I started. Something tells me that it's probably a pretty easy question, if I just knew where to begin. I need to calculate the longest wavelength (minimum frequency, right?) of light in nm that can be used to eject electrons from a surface, given that it takes 254kJ/mole. Can someone please help me!

Light comes in packets. How much energy that packet has depends on the frequency. You need to find the energy it takes to eject a single electron (remember the size of a mole?) and find the frequency of light that has that amount of energy per packet (or quantum).

Thank you, thank you, thank you, thank you, thank you! You are a life saver! I was trying to make things way too difficult!

You can get a better understanding of Quantum Mechanics basics through OCW courses. Check out the following ocw courses from MIT and TUFTS.
http://www.opencontentonline.com/search.php?query_text=quantum+mechanics

Cheers
Trilateral

Last edited by a moderator:

## 1. What is the relationship between wavelength and electron ejection?

The longer the wavelength of light, the more energy it carries. This energy is then transferred to the electrons, allowing them to gain enough energy to break free from the surface of the material, causing electron ejection.

## 2. How is the longest wavelength of light to eject electrons calculated?

The longest wavelength of light to eject electrons can be calculated using the equation: λ = hc/E, where λ is the wavelength, h is Planck's constant, c is the speed of light, and E is the energy threshold for electron ejection.

## 3. What is the energy threshold for electron ejection?

The energy threshold for electron ejection is the minimum amount of energy required for an electron to break free from the surface of a material. This threshold varies depending on the material and can be measured experimentally.

## 4. How does the material's work function affect the calculation of the longest wavelength of light?

The material's work function, which is the minimum amount of energy needed to remove an electron from the surface of a material, is directly related to the energy threshold for electron ejection. A higher work function will result in a higher energy threshold and therefore a shorter longest wavelength of light to eject electrons.

## 5. Why is calculating the longest wavelength of light to eject electrons important?

This calculation is important because it helps us understand the relationship between light and the behavior of electrons in materials. It also has practical applications, such as in the development of new technologies like solar panels and optoelectronic devices.

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