Any constant in physics or chemistry comes from experimental design and consistency in measurements. For example, if you divide multiple of pressure and volume with the multiple of moles and temperature, you will get the constant R for any ideal gas.
However, given how small planck’s constant is, how can we assume its accuracy?
In: Physics
The value of planck’s constant can be measured easily by employing a really simple photoelectric effect setup. You shine light on some photometal which has electrodes across it to generate potential difference and hence an electric field of desired strength, then you measure the current passing through the photometal. You increase the potential difference up until you see the current flowing through the material go to zero. This is the point where all the energy the photons have passed onto the photoelectrons has been “absorbed” by the field and they just can’t make it to the other electrode(they have no energy left at this point). Now you see the PD you’re at and multiply this by e because this is how much energy the electron had right before all of it got “eaten” up. The energy this electron had is equal to the energy the photon that hit it was. And you also know the frequency of the light you were shining on the photometal.
Now using E = h*f you can simply do h = E/f and congrats you’ve just calculated the value of planck’s constant!
The purpose of this whole thing was to just express that planck’s constant isn’t exactly “made up” but is a constant that can be experimentally verified. We also did Millikan’s oil drop experiment for it but I missed that lab so…
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