It's a little science history question but I really wonder how did peoples measured the amount of charge in an ball or something or like in coulombs case how did he measured the electrical force between two charged objects without knowing what is electrons? because in his formula we have to know the charges that two object has to be able to measure force between them.

I am just getting start to learning electrical forces, power, electrical components etc and I did as best as I can until now by learning and now I am about to start AC but before starting to learn about AC I feel like there is some gaps in my knowledge and that sometimes bothers me understanding new things, One of the biggest gap is this electrons and their nature or what are they exactly I have average chemistry knowledge so I know what are they and what they do in form of chemical reactions but how do they act in the form of electricity that we know is a little complicated in first sight but becomes more clear when you learn things one by one you start to understand nature of it because it is always the same thing happening in different forms and it is mostly predictable if not all, So after this novel and with my question at the top I would like to hear how do we know the amount of electrons that we use in our cables and machines so that we are using these electrons to measure many things about them and using many formulas that gives us all those ampheres, volts, coulombs etc.


Milliken proved that charge occurs in increments of $e$, and inferred that this increment is the charge on an electron. Milliken's experiment produced an aerosol of oil drops whose size could be measured with a microscope. The oil had a known density, so the weight of each drop could be calculated. The oil drops picked up various amounts of charge, pretty much at random. By adjusting the voltage between two flat horizontal plates, Milliken was able to exert a vertical electrostatic force on the drops, just enough to balance the force of gravity. By comparing the weight to the voltage, Milliken was able to determine the charge held by an oildrop. Looking at the results, he found that the charge was always an integral multiple of $e$.

Current can be measured by using the current to charge a capacitor, because the voltage across a capacitor is proportional to the amount of charge stored in the capacitor. So, the rate of change of voltage across the capacitor is equal to the current flowing into the capacitor.

There are of course many other ways to measure charge and current.

The Wikipedia article on electric charge has a good account of the history of the concept of charge. The inverse square law could have been obtained by observing the behavior of charged pith balls as the distance between them is changed.

I'm not sure how a standard charge or current was defined prior to Milliken's experiment. I suppose the force of attraction between two parallel wires carrying the same current at a standard distance apart would serve the purpose.

  • $\begingroup$ But Miliken did the experiment way later(1909) than calculating of the electrical force by Coulomb(1785') there must be an other way to predict the charge to calculate this force in the form of k.(q1.q2) / d^2 the q1 and q2 has to be the magnitude of the charges held by those two spheres. $\endgroup$
    – Tunguska
    Mar 1 '19 at 17:32
  • $\begingroup$ Please see my edit. $\endgroup$
    – S. McGrew
    Mar 1 '19 at 18:55

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