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# quantum physics

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1. What is light intensity? Is it the number of photons in the light?
What determines light intensity? Is it the frequency of the light, energy of the photon?
and one more thing why UV light bounces off photo electron but not visible light and other light? Is it because UV light has much shorter wavelength than visible light so it has higher frequency which means higher photon energy because E=hf
so sufficient energy to remove an electron from metal? does radio waves gives photo electron too?
thanx a lot!!!!
2. .....
3. Intensity is basically the no# of photons, per unit area, per second. With reference to photons, increasing Light intensity is increasing the no# of photons. Not their Energy.
Increasing the Frequency increases the Energy (E is directly proportional to F). Your explanation for Ultra Violet looks correct to me.
it all depends on the thresh hold frequency of the material. The materials with the lowest threshold frequencies are all semiconductors (i think ), so visible light should have a photoelectric effect. (im guess higher up the spectrum: green, blue, violet)
Radio waves are very large, so their frequency is low > have less energy> photo electric affect = no.
Hope i helped.
4. (Original post by MarshmallowBob)
Intensity is basically the no# of photons, per unit area, per second. With reference to photons, increasing Light intensity is increasing the no# of photons. Not their Energy.
Increasing the Frequency increases the Energy (E is directly proportional to F). Your explanation for Ultra Violet looks correct to me.
it all depends on the thresh hold frequency of the material. The materials with the lowest threshold frequencies are all semiconductors (i think ), so visible light should have a photoelectric effect. (im guess higher up the spectrum: green, blue, violet)
Radio waves are very large, so their frequency is low > have less energy> photo electric affect = no.
Hope i helped.
So increasing the intensity of light just means increasing the number photons. So if I increase the intensity of light then I will have more number of electrons per second than I had with UV light of low intensity.
Threshold frequency is kind of minimum frequency required to form photo electrons. Is it same like work function as work function is different for different materials so any of light from electromagnetic spectrum can cause photoelectric effect in different materials.
I can understand all other stuff but I dont understand this. Is there anything that determines intensity of light. I mean like we can change wavelength of light if we increase or decrease frequency so in the same way how can we change the intensity of light?
5. (Original post by AS01)
So increasing the intensity of light just means increasing the number photons. So if I increase the intensity of light then I will have more number of electrons per second than I had with UV light of low intensity.
Threshold frequency is kind of minimum frequency required to form photo electrons. Is it same like work function as work function is different for different materials so any of light from electromagnetic spectrum can cause photoelectric effect in different materials.
I can understand all other stuff but I dont understand this. Is there anything that determines intensity of light. I mean like we can change wavelength of light if we increase or decrease frequency so in the same way how can we change the intensity of light?
Intensity is directly proportional to the amplitude squared. An easy simple example of intensity would be a bright green light and a dim green light.
6. (Original post by MarshmallowBob)
Intensity is directly proportional to the amplitude squared. An easy simple example of intensity would be a bright green light and a dim green light.
it is bright and dim just due to different number of photons present on the light then?
7. yes.

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