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# Electricity watch

1. I have this question that i dont understand:
A 36W lamp draws a constant current of 3.0A over a period of 600s from a battery. Calculate the number of electrons passing through the lamp.

I have already worked out: the p.d across the lamp= 12V
the energy transferred by the lamp= 21600J
the charge passing through the lamp= 1800C

2. 1A = 1 coulomb per second, so for 3A in 600s how many coulombs?
Then 1 coulomb = how many electrons? (remember - 1 elementary charge = 1.602x10^-19 C)
Multiply these together and you're sorted.

I think
3. (Original post by alex193)
***
I see this is your first post in the physics study help section.
Thanks for helping.

However...
Can I direct you to the guidance notes for posting here
http://www.thestudentroom.co.uk/wiki...ring_questions

in particular the request not to provide complete solutions to numerical problems. The aim is to help the poster help himself. As he had almost got to the solution, a small prod in the right direction was all that was needed.
Thanks for your cooperation.
4. Oops, should probably have read that first
5. (Original post by alex193)
Oops, should probably have read that first
There may still be time to edit your post and simply delete the last line.

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