- #1
lyrebird
- 3
- 0
Homework Statement
In a photoelectric experiment using a sodium surface, you find a stopping potential of 1.85 V for a wavelength of 300 nm and a stopping potential of 0.820 V for a wavelength of 400 nm. From these data find the following:
a) a value for the Planck constant
b) the work function for sodium
c) the cutoff wavelength λ0 (the wavelength corresponding to the cutoff frequency) for sodium
Homework Equations
The Attempt at a Solution
a) For this, I calculated the frequencies (using c = fλ) to be 10^15 Hz and 7.5*10^14 Hz.
I then used my graphics calculator to graph the stopping potentials vs. the frequencies. This gave me the line
y = 2.427*10^14*x + 5.5097*10^14
The slope should be equal to Planck's constant divided by the charge on an electron. Thus,
Planck's constant = 92.427*10^14)(1.602*10^-19) = 3.89*10^-5
which clearly isn't right. Also, I am supposed to give the answer in eV·s. But isn't Planck's constant measured in m^2·kg·s?
b) The y-intercept of the line on the graph is the work function divided by the charge on an electron.
Work function = (5.5097*10^14)(1.602*10^-19) = 8.826*10^-5
Again, this doesn't seem right?
c) I presume that I'll be able to solve this once I know the answers to the previous parts, but I have absolutely no idea how to do it.