Finding out how many electrons have passed a point in the circuit

[mandos]

1. The problem statement, all variables and given/known data

Calculate the charge which has passed through a point in a circuit when there is a current of 6.3kA for 58 minutes. Calculate the number of electrons passing a point in the circuit.

How to work out the part in blue.

2. Relevant equations

We're told the charge of one electon is "e = -1.6 x 10^-19 C"

3. The attempt at a solution

Q = I x t

t = 58min = 3480 seconds.
I = 6.3 x 10^3

3480 x 6.3 x 10^3 = 2.2 x 10^7 (rounded up a bit as my college teacher told me to do).

But it's the part in blue I get stuck on. I actually already know the answer (also rounded up slightly I believe) is 1.4*10^26 but it's how I get to that answer using the information "e = -1.6 x 10^-19 C" and "Q = 22 x 10^7"

If someone could show me how to do it, so I can then practice doing so on the other questions I've got and learn it properly. Also, apologies if this is a really moronic question for some of you, browsing around you all seem to be quite intelligent ^^;

[learningphysics]

Take the total charge... 2.2*10^7C... and divide by charge/electron = 1.6*10^-19C/electron. That gives you the number of electrons.

[mandos]

2.2*10^7 / 1.6*10^-19 gives me 1.375^-12

I can see that 1.375 is rounded up to 1.4 but the power is still -12 and the answer the college teacher has given us is 1.4*10^26

[learningphysics]

2.2*10^7 / 1.6*10^-19 gives me 1.375^-12

I can see that 1.375 is rounded up to 1.4 but the power is still -12 and the answer the college teacher has given us is 1.4*10^26

The exponent is 1.6*10^-19. not +19.

[mandos]

I made it from negative nineteen to positive nineteen and got the right answer she said we should get.

So did she make a typo with multiply ten to the power negative nineteen?

[learningphysics]

I made it from negative nineteen to positive nineteen and got the right answer she said we should get.

So did she make a typo with multiply ten to the power negative nineteen?

No 1.6*10^-19 is right.

\frac{(2.2*10^7)}{(1.6*10^{-19})} should give you 1.375*10^26.

Did you divide correcty?

[mandos]

I'm either incredibly stupid or my calculator is playing mind games.

I'm inclined to believe it's the first one.

Thanks for all your help learningphysics. I've finally got it.

[learningphysics]

I'm either incredibly stupid or my calculator is playing mind games.

I'm inclined to believe it's the first one.

Thanks for all your help learningphysics. I've finally got it.

:wink: No prob. happens to all of us.