Finding and approximation for Planck's constant ( H )

[timethyfx2]

I have a HSC physics assessment task (Yr 12 Australia) due in a few days where we had to take measurements of the photoelectric effect (VStop, Wave no/length, F) etc with different filters and find an approximation for H, by manipulating different equations etc.

I already found an fairly close approximation (1.7e-34) H=6.626e-34, but i just want to no if my method was right or not.

The work function was found by graphing Kemax against the F (Kemax = QVstop/F). A trend line was extended back to get f (3.6e-34) Approx. An approximation for H was found by getting the gradient of the slope of KEMax + W / F (2e-34). But since excel rounded it a bit i put it in my calculater (H = QVstop + W]/F) and got 1.69e-34

So is that the rite way to do it or is there a better way
Thnx in advance 4 ne comments

 

[tyco05]

G'day mate,
I can't quite understand what you are getting at there, but... it seems as though you are on the right track. Also I don't know if this reply will help you in time.

The kinetic energy of the ejected electron, KE, is equal to the energy of the initial photon, hf, minus the work function of the apparatus.

ie:

KE = hf - W

which I think you understand.

Hence plotting KE vs f should yield a linear graph with gradient h and y intercept W (or -W as the case may be).

Excel can give h simply by plotting the trendline and then "show equation". BUT this will be a horribly rounded answer, especially if you are going to use it in further calculations (which it doesn't seem as though you are). A better way of doing it is... as you may well have done ... using the regression analysis tool.

Also don't forget to mention errors and uncertainties in your experiment. Was the filtered light perfectly monochromatic (one frequency??)
If you can get some error bars (or even boxes) on your graph, you can get a line of minimum gradient and a line of maximum gradient. This will give you some idea of the uncertainty in your result of 1.7E-34 .

 

[thepatientmental]

It sounds like you have used a valid method to approximate Planck's constant, H. By manipulating different equations and using the graphing method, you were able to come up with a value that is fairly close to the accepted value of H. It's important to note that there may be slight variations in your answer due to rounding or other factors, but overall it seems like you have a good understanding of the concept and were able to apply it effectively in your assessment task.

In terms of a better method, it really depends on the specific requirements and guidelines of your assessment task. However, some other methods that could potentially be used to approximate H include using the slope of the linear portion of the graph of kinetic energy vs. frequency, or using the slope of the linear portion of the graph of kinetic energy vs. wavelength. It's always a good idea to check with your teacher or refer to any provided resources for guidance on the best approach for your specific task. Keep up the good work and good luck with your assessment!