## Light intensity

$c=\lambda v$

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### Light intensity

In lecture, Dr. Lavelle kept mentioning the intensity of light versus frequency. I understand that the frequency of light depends on the wavelength, but how does the intensity change? And how is intensity measured exactly?

Chem_Mod
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### Re: Light intensity

Increasing light intensity increases the number of photons. If the energy per photon is greater or equal to the energy needed to remove an electron, then increasing light intensity results in more ejected electrons. Based on the photoelectric experiment, light sources with short wavelengths (high frequencies) can eject electrons (even with low intensity light).

Victoria Li 1L
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### Re: Light intensity

I think that light intensity is independent of the other two values. In a particle model of light, intensity is just the number of photons (e.g. higher intensity means more photons and thus more electrons ejected). In a wave model, intensity is just the amplitude. This is the post I referenced: https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=940

Hope this helped!

Claire Stoecklein 1E
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### Re: Light intensity

Intensity is synonymous with brightness. Two lightbulbs can have the same wavelength and frequency of light, but we can increase the brightness by turning both lightbulbs on instead of one. This shows that the amount of light doesn't have an effect on the energy hitting the electrons, but rather the amount of energy in each photon.

JohnWalkiewicz2J
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### Re: Light intensity

Hey!
Visually, the intensity of the light corresponds to its brightness. If we look at it from a quantum prospective, the intensity of light corresponds to the number of photons. Increasing the intensity increases the number of photons in the light.

Katherine Brenner 3H
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### Re: Light intensity

I am also confused on the correlation between light intensity and frequency. Would someone mind explaining the difference between the wave vs light model.

Hannah Romano 4D
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### Re: Light intensity

Light intensity refers to the brightness of the light. In terms of the wave model, this references the amplitude of the light. Greater amplitudes would correlate to greater intensities. Still, as far as the photoelectric effect goes, greater amplitudes do not determine whether electrons will be ejected. This is determined by meeting a specific frequency threshold for each metal type. Once this threshold is met, THEN greater intensities (amplitudes) will affect the result in the QUANTITY of electrons ejected because greater intensities will increase the quantity of individual photons for a certain frequency. Therefor, because each individual photon interacts with an individual e-, greater intensity of light will only increase the number of e- ejected, but not the energy of each e-.

Yiyang Jen Wang 4G
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### Re: Light intensity

I think intensity is effected by amplitude. Higher amplitude will result in higher intensity which will cause the light to be brighter. But Plz correct me if I am wrong!

Leila_4G
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### Re: Light intensity

Is there a difference between the energy per photon and the threshold energy?

Sebastian Lee 1L
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### Re: Light intensity

The energy per photon is equal to Planck's constant times frequency of each photon. The threshold energy (or work function) is how much energy is required per photon to eject an electron from the metal. If the energy per photon equals the threshold energy, then an electron will be ejected from the metal with kinetic energy = 0. If the energy per photon is increased by increasing frequency, then the excess energy will be the kinetic energy of the ejected electron. All that intensity does is increase the number of electrons ejected. Intensity is the number of photons so if 5 photons reach threshold energy, then 5 electrons will be ejected.

805097738
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### Re: Light intensity

Leila_4E wrote:Is there a difference between the energy per photon and the threshold energy?

if the energy per photon is greater than the threshold energy, there will be excess energy.