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i'm reading a book that it says :

If a current of 1A flows through a copper wire, the number of electrons flowing by a cross section of the wire in 1s is equal to :

1A=(1C/1s)(electron/-1.602*10^-19C)=-6.24*10^18 electrons/s

I really don't understand how he can have this result, what's the mean of electron into the division here ? Thanks for the help!

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  • \$\begingroup\$ charge is quantized. one electron has a charge of -1.6 10^-19 coulombs, so, how many electrons are required for one coulomb? (as for the minus sign, which I had forgot, it means that the electron movement is opposite to the conventional current direction) \$\endgroup\$ Mar 21, 2018 at 23:44
  • \$\begingroup\$ It requires 1/1.6 10^-19 electrons to have one colomb ? \$\endgroup\$ Mar 21, 2018 at 23:48
  • \$\begingroup\$ Yep, that's 6.25 x 10^18 electrons. \$\endgroup\$ Mar 21, 2018 at 23:51
  • \$\begingroup\$ Ok but i see that 1 colomb is equal to 6,241 509 629 152 65*10^18, why don't use this value into the division ? \$\endgroup\$ Mar 21, 2018 at 23:57
  • \$\begingroup\$ I guess the goal of the exercise was to compute that equivalence. Also, note that charge is one thing: you need 6.24 10^-18 electrons to have 1C, but current also involve time: in principle you could have much fewer electrons going in a circle at very high speed to attain the same 1A figure. \$\endgroup\$ Mar 21, 2018 at 23:59

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It tells you how many electrons will flow when a current of 1 A is applied for 1 s to a conductor. 1 ampere-second is actually 1 coulomb, the unit to measure charges. Every electron has a charge of -1.602*10^-19 C, so if you divide the charge flowing per second by the elementary charge of an electron, you get the number of electrons flowing per second.

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A charge in a medium defined by:

\$Q=It\$, current multiplied by the time duration.

Therefore, 1 ampere is defined by:

\$1A=1C/s\$.

So if you had 0.25 amperes in a duration of 10 seconds, that would mean:

\$0.25A = C/10\$, solve for \$C\$, you get 2.5 Coloumbs of charge.

Remember that current is the rate of charge in a given time period. Think of water for another analogy. Current is the flow rate of water given in a period of time. The same idea can be applied with electric current.

But as far as how many electrons are given in 1 ampere, you can solve for that as well. If one electron is \$\approx 1.062\times10^{-19} C\$, then if you have 1A of current in 1 second, you'll have a lot of electrons... like about 6241509128999772160 electrons.

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