Electron not emitted even for high intensity light

Moderators: Chem_Mod, Chem_Admin

LaurenChoi_1J
Posts: 60
Joined: Wed Sep 30, 2020 9:48 pm

Electron not emitted even for high intensity light

Postby LaurenChoi_1J » Wed Oct 14, 2020 8:00 pm

Can anyone explain the statement in the lecture where electrons are not emitted even for high intensity light?

cadytran1K
Posts: 83
Joined: Wed Sep 30, 2020 9:49 pm

Re: Electron not emitted even for high intensity light

Postby cadytran1K » Wed Oct 14, 2020 8:08 pm

Hi! I'm not sure if this will be much help, but in my notes I wrote that even though there is high intensity light, the energy of the light has to be equal to or larger than the energy to remove in order for the electrons to be emitted. Also, if the intensity increases, the number of photons double. However each photon has the same energy, so this wont eject electrons.

Nandhini Ekambaram 1L
Posts: 100
Joined: Wed Sep 30, 2020 9:58 pm

Re: Electron not emitted even for high intensity light

Postby Nandhini Ekambaram 1L » Wed Oct 14, 2020 8:22 pm

Hi! I was also a bit confused on that. I think increasing the intensity of the light would increase the number of photons present, but the each photon does not have enough energy to eject an electron. Increasing the number of photons does not allow them to add up all their energy. Each photon still acts as its own because of the one to one ratio between a photon and electron.

BrittneyMyint1D
Posts: 110
Joined: Wed Sep 30, 2020 9:59 pm
Been upvoted: 3 times

Re: Electron not emitted even for high intensity light

Postby BrittneyMyint1D » Wed Oct 14, 2020 8:38 pm

Hi! I believe you are talking about how electrons are not emitted, even for high intensity light, when the light has low frequency (long wavelength). This is because all the photons in this wavelength will have the same amount of energy.
If the photons in the wavelength do not have sufficient energy to eject an electron, then increasing the intensity of light (which means increasing the number of photons) would still not eject any electrons because no one photon in this wavelength will have enough energy to remove an electron. Thus, adding more photons/increasing the intensity of light will not eject any electrons if each photon does not have sufficient energy.
However, if the light has a higher frequency (shorter wavelength), each photon will have enough energy to emit electrons, so high intensity light would actually emit more electrons because adding more photons with enough energy will eject a more electrons (hopefully this isn't confusing you!)
Just keep in mind of whether the light has a short wavelength or long wavelength, since this determines whether the photons will have enough energy to eject electrons.
Hope this helps!

Karina Grover 1A
Posts: 91
Joined: Wed Sep 30, 2020 9:34 pm
Been upvoted: 1 time

Re: Electron not emitted even for high intensity light

Postby Karina Grover 1A » Wed Oct 14, 2020 8:45 pm

Hi!

This is based on my understanding... If light exhibited ONLY wave properties, then increasing the intensity (i.e. higher amplitude) should increase the number of electrons emitted. However, light exhibits BOTH wave and particle properties. Thus, if the frequency of light is too low, then increasing the intensity will not have any effect on electron emission.

I hope this helps!

Crystal Pan 2G
Posts: 112
Joined: Wed Sep 30, 2020 10:04 pm
Been upvoted: 2 times

Re: Electron not emitted even for high intensity light

Postby Crystal Pan 2G » Wed Oct 14, 2020 8:47 pm

Energy(photon) must be greater or equal to work function in order for an electron to be emitted. if light only had wave properties, then increasing intensity should eject electrons(in wave model, intensity would be amplitude), but we need to consider light as photons(packets) of energy. So frequency must be high enough per photon to eject an electron. higher intensity = more photons, but not the amount of energy per photon. hope that made sense.

Joey_Okumura_1E
Posts: 116
Joined: Wed Sep 30, 2020 9:58 pm

Re: Electron not emitted even for high intensity light

Postby Joey_Okumura_1E » Wed Oct 14, 2020 8:56 pm

Intensity describes the amount of photons. However, the amount of photons does not matter because only one photon can be used to eject an electron. Therefore, an electron will not be ejected unless a photon has sufficient energy.

Bella Bursulaya 3G
Posts: 133
Joined: Wed Sep 30, 2020 9:54 pm

Re: Electron not emitted even for high intensity light

Postby Bella Bursulaya 3G » Wed Oct 14, 2020 9:04 pm

Intensity in a wave model is related to the amplitude of the wave. At the beach, a larger amplitude of a wave has more energy to knock you down, and a small one won't do you much harm. We thought light, since it acts as a wave, should behave the same, and increasing the intensity (amplitude) would increase the energy.

However, light can also behave as a particle, which means it is quantized. It is made up of photons, or individual packets of energy. If you increase the intensity (number of photons) the overall energy will increase (a more intense light will warm up an object faster and with a higher temperature than a low intensity light), but the energy of each individual photon will not increase. You need a certain energy of a photon to emit an electron, and no matter how many you have, if none of them can emit an electron, none of them will.

Imagine you're at a golf range, and you came with friends. All of you are weaker than the professional golfer, and can't hit, say, 350 yards. No matter how many of you there are, none of you will be able to hit it that far. None of you have the energy to hit it that far, just as the photons don't have the energy to remove that electron.

Hope this helps!

Chinyere Okeke 2J
Posts: 88
Joined: Wed Sep 30, 2020 10:05 pm
Been upvoted: 1 time

Re: Electron not emitted even for high intensity light

Postby Chinyere Okeke 2J » Wed Oct 14, 2020 9:38 pm

Basically, in the photoelectric effect for an electron to be emitted the energy of the light needs to be high enough that it meets the threshold energy of the electron. The scientist who found the photoelectric effect discovered that even when they increased the intensity of the light the electrons would not emit if they had not done so before. This meant that light wasn't acting as a wave, since when light acts as a wave increasing intensity increases amplitude which in turn is an increase in energy. This meant that the light had particle properties.

So since light is acting as particles, the energy of A SINGLE photon has to be high enough to excite A SINGLE electron. And when you think of light as photons, increasing the intensity just means HAVING MORE photons, NOT changing the energy of a photon. SO in the photoelectric effect increasing the intensity of a light source doesn't increase the number of electrons emitted since it doesn't increase the energy per photons. Instead increasing the intensity increases the amount of photons which is useless, unless each photon has enough energy to match the threshold energy of an electron.

Ariel Guan 1H
Posts: 91
Joined: Wed Sep 30, 2020 9:36 pm
Been upvoted: 1 time

Re: Electron not emitted even for high intensity light

Postby Ariel Guan 1H » Wed Oct 14, 2020 10:01 pm

In the lecture, he said that light wasn't acting like a wave, which means that intensity would not increase energy. He said to instead look at light as little packets of energy, and remember that one photon must have enough energy to eject one electron. However, increasing the intensity would only increase the amount of photons present, but not the energy of those photons. Instead, the frequency affects the energy of the photons; a high enough frequency means photons w/ sufficient energy, which means electrons will be emitted. If the energy per photon is high enough to emit an electron, then an increase in intensity would mean that more electrons will be ejected (as more photons will be present). Also remember that light with short wavelengths have high frequencies, so they can eject electrons even when there is a low intensity of light.


Return to “Photoelectric Effect”

Who is online

Users browsing this forum: No registered users and 2 guests