Why is coulomb chosen as the unit of charge? why not the charge of an electron chosen as fundamental unit?

Question

The charge of electron is -1.6*10^-19 coulombs. The charge of electron is the fundamental charge. Then why cant we take the charge of electron as the unit of charge? Why cant we choose the sign of charge differently i.e. the charge of electron is positive? Are there any advantages or disadvantages if the charge of electron taken positive? Why should the unit of charge be coulomb, which is the charge of a mol of electrons? What is the importance of mol?

Answer 1

1. When unit of charge coulomb came into being the electron was unknown to the world (C. A. Coulomb 1736 – 1806), let along the magnitude of its charge. Also the electron has such a microscopic charge.
2. It makes little difference if an electron is positive or negative, however since we all just happened to agree to it being called negative so the rest will fall in their relative places.
3. Mol (see Avogadro's number http://en.wikipedia.org/wiki/Avogadro%27s_number) is a way of saying that we have enough electrons to some standard. The mole is the standard method for communicating how much of a substance is present.

Answer 2

We can choose the electron as the unit of charge.

But a unit is chosen taking into consideration, so many other factors also. The main choice is that it must be a practical unit that is used in day to day life by common people and also by other field of science, especially in engineering.

Further, since we know the conversion factors, the unit is changed if the circumstances force it.

For example, in macroscopic things kg is taken as unit of mass and in microscopic world atomic mass unit is chosen. According to need distances are measured in km, nano meter and in light year also.

However, there must be a fundamental unit that is defined; it can be anything and should be universally accepted; that is all.

Similar conclusion is for the sign of electron. In the beginning, positive charges are considered for the flow of charges; to retain the convention electrons are designated as negative and to avoid unnecessary confusion in the minds of non-physics subjects the custom is allowed to continue.

There is no special advantage in changing the conventional things.

Same is with mole.

Answer 3

As others have noted, there was no precise knowledge of the value of the quantum of electric charge when the unit of charge was being formed. However, the coulomb was not chosen arbitrarily. It was made as a derived quantity from the ampere, which was defined as that current which, if travelling in two segments of thin, parallel wire one metre apart, exerts a force between the wires of 2e-7 newtons per metre of wire. Why 2e-7? Well, that was inherited from the earlier CGS-EMU units, but that's another story. The reference has more details

Answer 4

Your question is an historical one as to the particular circumstances under which the unit of charge was choosen. The answer is that scientists defined what electrical chage was before they knew what the charge of an electron was. After that historical event, your question becomes a political one as to why, after Robert Millikan's oil-drop experiment in 1909, don't scientists change the convention to the charge of an electron.

The answer is that once a convention is accepted by the community, it is hard to change. You might as well ask why we still use inches and feet in the USA. Perhaps you could think of the answer as psychological as in "people are stubborn" or "people don't like change."

Answer 5

Because then a 13 Amp plug would become a 7,800,000,000,000,000,000,000,000 Amp plug (current is a derived unit charge/sec). This would not fit on the label.