Help with relating Current and Charge

[RafaFutbol]

1. First Question

A car battery is rated at 90 A hr, meaning that it can supply a current of 90 A current for 1 hr before being completely discharged. If you leave your headlights on until the battery is completely dead, how much charge leaves the battery?

Can charge be related to the current as well? Since current is the flow of charge, can it just be said that Q = It, where t is 3600 seconds, and I is 90 A?

so then Q = (90)(3600) = 3.24 * 10^5 C

Is this correct?

Second Question

What is the potential difference across a 20-m long, 2.0 mm diameter copper wire carrying an 8.0A current?

We know that E = V/L, and that I = (A/p) * E, so then E = (I*p)/A

then we can relate them as V = (I*p*L)/A

We have I, L and A, but how would I get p from the information given?

Thanks for the help guys!

 

[LowlyPion]

1. First Question

A car battery is rated at 90 A hr, meaning that it can supply a current of 90 A current for 1 hr before being completely discharged. If you leave your headlights on until the battery is completely dead, how much charge leaves the battery?

Can charge be related to the current as well? Since current is the flow of charge, can it just be said that Q = It, where t is 3600 seconds, and I is 90 A?

so then Q = (90)(3600) = 3.24 * 10^5 C

Is this correct?

Second Question

What is the potential difference across a 20-m long, 2.0 mm diameter copper wire carrying an 8.0A current?

We know that E = V/L, and that I = (A/p) * E, so then E = (I*p)/A

then we can relate them as V = (I*p*L)/A

We have I, L and A, but how would I get p from the information given?

Thanks for the help guys!

Looks ok to me.

 

[nlightner]

Yes, your calculation for the first question is correct. Q = It is the formula for charge, where Q is charge in coulombs, I is current in amperes, and t is time in seconds.

For the second question, you can calculate the resistivity (p) of copper using the given diameter and the known resistivity of copper (1.68 x 10^-8 ohm-m). Then you can use the formula V = IR to calculate the potential difference across the wire.