# What is a coulomb

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If we can’t measure singular electrons then how can we measure these

In: Physics

A coulomb is a measure of charge. You can measure a coulomb worth of charge despite not counting electrons for the same reason that you can measure a gram despite not counting atoms: it’s easier to measure a large amount of something.

It’s a unit of charge. We can measure coulombs easier than the charge of an individual electron because a coulomb is a much larger unit. Like, your bathroom scale can measure something that weighs in the tens of kilograms, but it isn’t sensitive enough to measure the mass of a speck of dust that weighs one microgram.

A coulomb is a unit of charge. It’s the charge that’s transferred by one ampere in one second. It, unfortunately, doesn’t work out to be the charge of a whole number of electrons, so no physical object can have a charge of exactly one coulomb under normal circumstances.

The same as anything else. If you can’t measure a single electron, measure 2 trillion electrons then divide by 2 trillion.

To answer a slightly different question, the charge on an election was determined without needing to measure a single electron.

The most famous experiment to do this was [Millikan & Fletcher’s oil drop experiment](https://en.wikipedia.org/wiki/Oil_drop_experiment), published in 1911, and which won Millikan the 1923 Nobel Prize.

In that they got small drops of oil and moved them in an electric field to work out the charge of the oil droplet.

They repeated this for lots and lots of droplets, and found the largest number they could which divided into them. For example, if they had got 15, 27, 39, 51 as their values, they would conclude that the smallest charge was a 3 (or a factor of 3).

By doing the experiment enough times, getting enough numbers, they were fairly confident that their result; 1.5924(17)×10^(-19)C – was the smallest unit of charge possible in an oil drop.

Unfortunately some of their input data wasn’t quite right, and there were problems with them ignoring data to get a more precise result. Their result wasn’t right. But it was still far closer than anyone else had got. The current best answer is 1.602176634×10^(−19) C, although that is kind of cheating as that is used to define 1C, rather than measure the charge on an electron.

No experiment has ever found evidence to suggest smaller charges (on their own).

A coulomb are 6,2 * 10^18 electrons.

Measuring a single electron is hard but possible. Measuring a large group of electrons is far easier.