# Physics fields and chem combined question

If a standard 100W light bulb needs 120V to shine, determine how long I could run the light bulb if I used up all the electrons in a copper penny to power it. Assume the penny to have a mass of 5.0g. Hint: think back to the units that make up watts and volts

Doc Al
Mentor
This is a wierd, non-physical question!

I assume they want you to figure out the current flowing through the bulb. Can you do that?

Once you have the current (I), then the total charge (Q) that flows per time (t) is: I = Q/t (that's the meaning of current).

To find the number of electrons in the penny: first find the number of copper atoms. (Hint: you'll need the atomic mass of copper) Then, depending on how wacky your teacher is, find the number of electrons: does he mean ALL electrons? or just the "free" electrons in the outer shell? I would use one electron per atom.

Then consider the charge on the electron. How many "electrons"/sec have to flow to make one Amp of current?