Planck's Constant measured in photoelectric effect

In summary, a student is performing the photoelectric experiment in an advanced laboratory class. The stopping potential is measured for two different wavelengths of ultraviolet light, 285 nm and 207 nm, and the values are 2.61 V and 4.53 V, respectively. The question is to find the work function of the metal. The equation used is hf = eV + φ, and after manipulating it, the value of φ cannot be solved for. However, it is mentioned that this is part 1 of the problem and part 2 involves finding Planck's constant based on the measurements.
  • #1
jimmypoopins
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Homework Statement


In an advanced laboratory class a student performs the photoelectric experiment. Ultraviolet light is shone on a particular metal and the stopping potential is measured at the same time. It is found that 2.61 V is needed to stop all the electrons when the wavelength of the light is 285 nm, and 4.53 V for a wavelength of 207 nm. What is the work function of the metal?

Homework Equations


[tex]hf=eV+\phi[/tex]
Find [tex]\phi[/tex]

The Attempt at a Solution



(1)[tex]hf_{1}=eV_{1}+\phi[/tex]

(2)[tex]hf_{2}=eV_{2}+\phi[/tex]

divide 1 by 2 to get rid of h, and we get

[tex]\frac{f_{1}}{f_{2}}=\frac{eV_{1}+\phi}{eV_{2}+\phi}[/tex]

i can't seem to solve for [tex]\phi[/tex] and get the correct answer. I've tried doing it both algebraically(sp, sry) and with a calculator. possibly I'm putting the numbers in wrong? i have:

[tex]e=1.6022*10^-19 C[/tex]

[tex]f_{1}=285*10^-9 m[/tex]

[tex]f_{2}=207*10^-9 m[/tex]

[tex]V_{1}=2.61V[/tex]

[tex]V_{2}=4.53V[/tex]

where am i going wrong? please help
 
Last edited:
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  • #2
Should you need two wavelengths to measure the work function in this experiment?
 
  • #3
my apologies, i should have added something not stated in the problem. the second part of this problem is stated:

2. What is Planck's constant based on this measurement?

from this i assume that h is an unknown for part 1. my reasoning is that this is an experiment, and Planck's constant is not exact; it is just supposed to be calculated from four measurements someone took in a lab.
 

What is Planck's Constant?

Planck's Constant is a fundamental constant in physics that is used to relate the energy of a photon to its frequency. It is denoted by the symbol h and is approximately 6.626 x 10^-34 joule seconds.

How is Planck's Constant measured?

Planck's Constant is typically measured using the photoelectric effect, which involves shining light on a metal surface and measuring the energy of the electrons that are emitted. By varying the frequency of the light, the relationship between energy and frequency can be determined and used to calculate Planck's Constant.

Why is Planck's Constant important?

Planck's Constant is important because it is used in many areas of physics, including quantum mechanics, atomic and molecular physics, and spectroscopy. It is also a fundamental constant that helps to explain the behavior of particles at the atomic and subatomic level.

How was Planck's Constant first discovered?

Planck's Constant was first discovered by German physicist Max Planck in 1900, as part of his research on blackbody radiation. Planck proposed that energy is quantized, meaning it can only exist in discrete units, rather than being continuous. This led to the discovery of Planck's Constant and laid the foundation for the development of quantum mechanics.

What is the value of Planck's Constant?

The value of Planck's Constant is approximately 6.626 x 10^-34 joule seconds, as determined by numerous experiments and measurements. However, due to limitations in measurement technology, this value may have a small margin of error. It is considered a fundamental constant and does not change in different situations.

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