Problem with photoelectric effect

In summary, the conversation discusses the photoelectric effect and determining the largest and minimum wavelengths of light that will result in electron emission from a photosurface. The equation eV=hf-W is used to calculate the work function and the threshold frequency. The potential required to stop electron emission is also discussed, with no real restriction on the minimum wavelength as long as it is shorter than the threshold wavelength. The conversation also includes some confusion between wavelength and frequency, but ultimately concludes that as long as the photons have a shorter wavelength than the threshold wavelength, there will be electron emission.
  • #1
ant284
Hi,

I'm have a problem with photoelectric effect
it states that we have a wavelength of 2.08*10^-7 falls on the photosurface, a voltage of 1.40V is required to stop the emitted electrons from reaching the anode.
What is the largest wavelength of light which will result in emission of electrons from this photosurface.?

so we have the equation
eV=hf-W
W=h* critical frequency and
K=hf-W
and
f=speed of light/wavelength.

v=1.40
f=(3*10^8)/(2.08*10^-7)

And wouldn't the Kinetic energy be 0 for a wavelength of 2.08*10^-7
So i don't know where to go from here! I want to do it but I can't it is frustrating!
Any help is appreciation
 
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  • #2
Hi again,

I think i got it

we have
K(kinetic)= eV
eV=hf-W
1.4 * (1.6*10-19) = h c/wavenlength -work
we get work =
7.7*10^-19 (About)
Now when it is the largest value above this value no electron will be emitted therefore KE=0
so we would have
0= Hc/waveleng-W
or
hc/w=wavelength
and we get 2.6*10^-7

But my question what would be the minimum value of wavelength?? if it is possible to find
 
  • #3
Your answer to the question is right (I got 272 nm without rounding). As for a minimum wavelength - there isn't really a restriction on how short wavelength the light is aslong as it is shorter than the threshold (maximum) wavelength. It's just that a higher potential would be needed to stop emission.
 
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  • #4
Hi,

one more quick question, as long as the frequency is below the threshold electrons are emitted, and above the threshold, the electrons are not emitted? Am i correct
 
  • #5
Damn sorry I've probably just confused you now. I've editted my original to say wavelength instead of frequency (oops). Aslong as the photons are above the threshold frequency, or below the wavelength at this frequency will there be emission. Sorry I kept swapping wavelength and frequency and probably confused us both!

Anyway to make it clear again - aslong as the photons are above the threshold frequency, or have a shorter wavelength than the wavelength at this frequency there will be electron emission. So there is really no minimum wavelength value. lol :wink:

editted: about 10 times for spelling and grammar
 
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1. What is the photoelectric effect?

The photoelectric effect is a phenomenon in which electrons are emitted from a material when it is exposed to light of a certain frequency. This effect was first observed by Heinrich Hertz in 1887, and later explained by Albert Einstein in 1905.

2. What is the problem with the photoelectric effect?

The problem with the photoelectric effect is that according to classical electromagnetic theory, the energy of the emitted electrons should depend on the intensity of the light, not its frequency. However, experimental results showed that the energy of the emitted electrons depended on the frequency of the light, which could not be explained by classical theory.

3. How did Einstein solve the problem with the photoelectric effect?

Einstein proposed that light is made up of packets of energy called photons. Each photon has a specific frequency and energy, and when it strikes a material, it can transfer its energy to an electron, causing it to be emitted. This explanation was in line with the experimental results and helped to lay the foundation for quantum mechanics.

4. What is the significance of the photoelectric effect?

The photoelectric effect has significant implications in various fields, including solar energy, photography, and electronic devices. It is the basis for solar panels, which convert light energy into electrical energy. It also plays a crucial role in digital cameras, as well as in photocells used in light sensors and switches.

5. How is the photoelectric effect relevant in modern research?

The photoelectric effect remains an essential topic in modern research, particularly in the field of quantum mechanics. It has led to the development of new technologies, such as photovoltaic cells, which have become an increasingly popular source of renewable energy. Scientists are also continuing to study the photoelectric effect to gain a better understanding of the fundamental principles of quantum mechanics and the behavior of light.

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