Why we take direction of current opposite to direction of electron. As electrons moves in a circuit. And I read in my books that it is conveniently taken if it so how galvanometer works (gives direction of current)
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As many things in physics, it’s a convention. This particular one has an historical origin, in that we didn’t knew that the “negative” charges were the ones who move. If you actually think about it however, as I once read, if we had named the charges in reverse (so name “positive” what we call “negative”) then this convention of current would make more sense, but it didn’t go that way.
I think this is a good question, because it makes you think about how much of physics is conventions: the important thing about these is that you know them, so you can use them as an advantage, and break free from them.
For example, the Coulomb Law is defined with the constant
$\frac{1}{4\pi\epsilon_{0}}$, using the $C$ Coulomb as a unit of charge, but you can very well change the convention and set the constant to 1, as many textbooks do; what really matters is the functional form of the law.
Martino Wong
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