Why do we get a really low value for Planck's constant? (1 Viewer)

[Pyramid]

So, after measuring the voltage required to stop the photoelectron current induced by light of varying frequences, and graphing Frequency against Kinetic Energy (which is equivalent to stopping voltage), the gradient of our LOBF should equal Planck's constant of about 6.6.

-- However, most of my class got a gradient of ~4.5

So there is some major source of error that lowers the gradient of our graph, or in other words, that reduces the rate at which we have to increase stopping voltage when we increase the frequency of incident light.

What could it be?

 

[alcalder]

Look at your experiment set up and ask yourself, which bits of the experiment may not exaactly match the perfect physics world. eg do you need a perfect vacuum, frictionless surface etc.

Then you will have your answer.

 

[k02033]

isn't the initial kinetic energy = stopping voltage times the electron charge? not just stopping voltage. So if you just measured the kinetic energy as the stopping voltage, your energy values are much higher than they should be. By the way, did you plot the frequency on the y axis? The typical set up should be eV on y axis and f on the x axis, gradient of which is h. And y intercept is the workfunction

 

[Diaz]

I suspect it's your units - while Planck's Constant is around 6.6 x 10^-34 J s, it's only 4.13ish x 10^15 eV s. If your kinetic energy is measured in eV, that should be around what you'd get. Especially if you took kinetic energy as equal to the stopping voltage, in which case your energies would definitely have been measured in eV.