How can we be sure of Planck’s constant when we have never measured anything to that accuracy?

Question

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

Answer 1

So it’s a two step process.

Step 1, measure e/h using a SQUID https://en.m.wikipedia.org/wiki/SQUID . I did this in the lab as an undergrad: it’s fiddly and needs liquid helium, but nowhere near impossible. Your signal to noise ratio is gigantic because of the superconductor involved.

Step 2, measure e using e.g this method https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4914236/#:~:text=The%20charge%20of%20the%20electron,Vs%2C%20across%20the%20capacitor.

This allows you to calculate h directly by dividing the result of step 2 by the result of step 1.