## 'light intensity'

$c=\lambda v$

Cavalli_1H
Posts: 55
Joined: Thu Sep 19, 2019 12:15 am

### 'light intensity'

in lecture Lavelle talked about the relationship between the intensity of light and frequency/wavelength of light. can someone explain this correlation? also, how do we gauge intensity of light?

Alex Tchekanov Dis 2k
Posts: 81
Joined: Sat Aug 24, 2019 12:16 am

### Re: 'light intensity'

So the most important thing to remember is that if a certain wavelength of light does not cause electrons to be emitted, increasing or decreasing the intensity will not change the fact that electrons are not emitted. This is because the relationship between wavelength and energy. The equation E= hv and c=(wavelength)v can be used to illustrate the relationship between wavelength and energy. Thus only a light source with a specific energy level (or specific wavelength) will allow electrons to be emitted. Then, when you increase the intensity of the light source with the correct energy level, more electrons will be emitted. This is because a higher intensity means a higher number of photons.

Ethan Lam 4A
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Joined: Thu Jul 11, 2019 12:17 am

### Re: 'light intensity'

Since light has particle and wavelike properties, light intensity depends on which property. In regards to particle properties, light intensity increases when when the number of photons increase. For wavelike properties, the intensity increases with the amplitude of the wave.

Jonathan Gong 2H
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Joined: Sat Jul 20, 2019 12:16 am

### Re: 'light intensity'

The relationship between the intensity and frequency of light is that as frequency increases, intensity increases- so essentially, they are proportional. This is because intensity is generally gauged as the energy per some unit of time and according to the energy equation of light where E=hv, as frequency increases, energy increases. And, as for how wavelength factors in, according to c=wavelength*v, as wavelength increases, frequency goes down and energy/intensity goes down as well. So wavelength is inversely proportional with intensity. Hopefully this is right and helps you out.

SarahCoufal_1k
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Joined: Thu Jul 25, 2019 12:17 am

### Re: 'light intensity'

I think increasing intensity of light only increases the amplitude/height of a wave but does not change wavelength or the energy emitted. So more photons would be emitted but the energy of each photon wouldn't change. To change the energy of a light wave, the frequency has to change. As we learned, shorter wavelengths/ higher frequency has more energy.

In the photoelectric effect, it is a 1 photon: 1 electron interaction. So when the one photon isn't enough energy it can't remove the electron. Even if you increase the amount of electrons i.e the intensity of light, there would be more photons released but none are able to remove electrons.

However, when the photon has enough energy, it can remove the electron, then when you increase the intensity, there are more photons that are able to remove electrons.

Ashley Kao 1H
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Joined: Thu Jul 25, 2019 12:16 am

### Re: 'light intensity'

Intensity can be defined as the number of incoming photons whereas the frequency of light can be determined by the amount of cycles that occur per second. Thus, when we analyzed the photoelectric experiment during a lecture, it is apparent that the amount of electrons emitted from the model only increases by increasing frequency. Seeing that only one photon can work with each electron, increasing the intensity, and thus the amount of photons, would not have an effect on the excitement of the electrons. On the other hand, by increasing frequency, or the amount of cycles per second, the amount of energy engaging within the electron from the photon would increase. This would allow electrons to be emitted more frequently and at a faster rate.

PranaviKolla2B
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### Re: 'light intensity'

What exactly is the relationship between frequency and black bodies?

505306205
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Joined: Thu Jul 25, 2019 12:15 am

### Re: 'light intensity'

Black body refers to anything that absorbs all forms of electromagnetic radiation, regardless of frequency.

Kristina Rizo 2K
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Joined: Wed Sep 18, 2019 12:19 am

### Re: 'light intensity'

Jonathan Gong 1A wrote:The relationship between the intensity and frequency of light is that as frequency increases, intensity increases- so essentially, they are proportional. This is because intensity is generally gauged as the energy per some unit of time and according to the energy equation of light where E=hv, as frequency increases, energy increases. And, as for how wavelength factors in, according to c=wavelength*v, as wavelength increases, frequency goes down and energy/intensity goes down as well. So wavelength is inversely proportional with intensity. Hopefully this is right and helps you out.

Okay I really appreciate your explanation because I remembered Professor Lavelle talking about the inverse of wavelength but must have switched it in my notes and wrote that it was inversely related to frequency. But you are saying that the wavelength is inversely related to intensity, and intensity is proportional with frequency.