Calculate number of electrons... Watch

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young ajay
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Hey people

I'm really stuck on this Physics AS question from my AQA book:

1) Calculate the number of electrons passing a point in the wire in 10 minutes when the current is 5.0A

If someone could post on how I would go about working this out that'd be excellent. I'm rather stupid at times so please explain things in a lot of detail. I've already got the answer, I just have no idea on how to work it out.


Thanks in advance!
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Jedicake
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Charge = Current x Time.

Then you get the total charge passing that point in the wire. You know the charge on an electron (1.6x10^-19 C) so what can you do now?
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young ajay
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(Original post by Jedicake)
Charge = Current x Time.

Then you get the total charge passing that point in the wire. You know the charge on an electron (1.6x10^-19 C) so what can you do now?

Charge = 5.0A x 600seconds

Charge = 3000 Columbs

Charge of electron = 1.6x10^-19 C

3000 x 1.6x10^-19 = 4.8 x 10 ^-16

Wrong answer, have I made a mistake? :confused:
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thegodofgod
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(Original post by young ajay)
Charge = 5.0A x 600seconds

Charge = 3000 Columbs

Charge of electron = 1.6x10^-19 C

3000 x 1.6x10^-19 = 4.8 x 10 ^-16

Wrong answer, have I made a mistake? :confused:
It's 3000 / 1.6x10-19, because 1 electron has a charge of 1.6x10-19 C.
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Jedicake
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(Original post by young ajay)
Charge = 5.0A x 600seconds

Charge = 3000 Columbs

Charge of electron = 1.6x10^-19 C

3000 x 1.6x10^-19 = 4.8 x 10 ^-16

Wrong answer, have I made a mistake? :confused:
Very close but you have to divide 3000 by 1.6x10^-19.

Total charge/charge on electron = number of electrons.
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PatrickD
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(Original post by young ajay)
Charge = 5.0A x 600seconds

Charge = 3000 Columbs

Charge of electron = 1.6x10^-19 C

3000 x 1.6x10^-19 = 4.8 x 10 ^-16

Wrong answer, have I made a mistake? :confused:
You need to divide 3000 by 1.6 x 10-19 instead of multiplying because you're working out how many electrons make up that 3000 coulomb charge.

This will give a very high answer (of 1.875 x 1022) which you know is a sensible answer because a lot of electrons must pass through in 10 minutes, especially to add up to a 3000 coulomb charge.
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young ajay
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I couldn't get it to work, but I've found my own solution. Here it is in case anyone else needs it:

1A in 1 second = 1C
5A in 1 seconds = 5C
5A in 10 minutes (600 seconds) = 3000C

1 C = 6.25 x 10^18 electrons

C x electron

3000 x (6.25 x 10^18) = 1.9 x 10^22 (rounded = correct answer)


Thanks for all replies!
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ajayyy
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omg my name is ajay and iwas just having the same problem...lool thanks thooo
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