Finding planks constant from photoelectric effect

In summary, the conversation discusses an experiment involving shining different colors of light onto a cathode and applying negative voltage to the anode to obtain the average stopping potential for each wavelength. The gradient of the graph multiplied by the charge of the electron gives Planck's constant. The main question is whether the line of best fit goes through the origin or not, and what equation describes the photoelectric effect. The conversation also mentions the discrepancy between the theoretical and observed stopping potential values and suggests plotting a theoretical stopping potential vs. frequency curve.
  • #1
hayyan1
9
0

Homework Statement



Hello, i was doing an experiment in which you shine different colours of light onto a cathode and apply negative voltage to the anode so that the photo current reduced to a constant value.
I obtained the average stopping potential for each wavelength of light (green yellow blue violet turquoise) and now i was going to plot average stopping potential versus frequency. Now the gradient of this graph multiplied by the charge of the electron gives me Plancks constant (h=e(ΔV/Δf)).
However my problem is, does the line of best fit go through the origin or not?
 
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  • #2
What is the equation that describes the photoelectric effect? Why does the slope give you Planck's constant?
 
  • #3
i have the equation
e(electron charge) x V(stopping potential)= h(plancks constant) x f(frequency)
 
  • #4
Well, if that is the equation, you should know what the intercept on the axis is!

How do you derive that equation?
 
  • #5
huh? all I am saying is that i plotted average stopping potential on y-axis and frequency on x-axis, and all i want to know is that would my line of best fit go through (0,0) or not.
 
  • #6
Does the photocurrent drop to zero when a potential across it is equal to the kinetic energy of electrons?, because i found this not to be the case, the photocurrent reached a steady value that didnt decrease further, as i increased the potential across the anode and cathode..
 
  • #7
hayyan1 said:
huh? all I am saying is that i plotted average stopping potential on y-axis and frequency on x-axis, and all i want to know is that would my line of best fit go through (0,0) or not.

Yes, and I'm saying you should be able to work this out from the equation for the photoelectric effect. So please plot the theoretical stopping potential vs. frequency curve, and see if it goes through (0,0).

Hint: Your equation is not quite correct.
 

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 electromagnetic radiation, such as light. This effect was first observed by Heinrich Hertz in 1887 and was later explained by Albert Einstein in 1905.

2. How is the photoelectric effect related to Planck's constant?

The photoelectric effect is directly related to Planck's constant, which is a fundamental constant in quantum mechanics. Planck's constant represents the proportionality between the energy of a photon and the frequency of the electromagnetic radiation. This means that the photoelectric effect can be used to measure Planck's constant.

3. What is the equation used to find Planck's constant from the photoelectric effect?

The equation used to find Planck's constant from the photoelectric effect is known as the photoelectric equation:

h = (Ek - W) / f

where h is Planck's constant, Ek is the kinetic energy of the emitted electron, W is the work function (the minimum amount of energy needed to remove an electron from the material), and f is the frequency of the incident light.

4. How is the photoelectric effect experimentally performed to determine Planck's constant?

In the photoelectric effect experiment, a metal plate is connected to a power source and placed in a vacuum chamber. A light source with a known frequency is directed at the metal plate, causing electrons to be emitted. The emitted electrons are then collected and their kinetic energy is measured. By varying the frequency of the light source and measuring the corresponding kinetic energy of the emitted electrons, Planck's constant can be calculated using the photoelectric equation.

5. Why is determining Planck's constant important?

Planck's constant is a fundamental constant in quantum mechanics and is crucial for understanding the behavior of subatomic particles. It has numerous applications in fields such as physics, chemistry, and engineering. Additionally, determining Planck's constant allows for a better understanding of the nature of light and the relationship between energy and frequency in electromagnetic radiation.

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