2 more physics questions I need help on, please?
posted by physicsclass on .
In which of these situations does more charge flow past a given point on a wire?
a. Current of 4 A in 1 min
b. Current of 2 A in 0.5 min
c. Current of 8 A in 2 min
d. All are the same charge
I think the answer is C? Since the formula for finding current is 1 = C / s = 1 Ampere. So wouldn't I just have to multiply the current and minutes to get the net charge?
How long would it take for a net charge of 2.5 C to pass a location in a wire if it is to carry a steady current of 5 mA? I know in order to convert mA to amps, divide by 1000, so 5/1000=5x10^3A. Now what do I do? I thought I'd have to switch the original formula around so I divide the net charge by the current to get the time?

current in amps is coulombs of charge per second
I = Q/t
so
Q = I t
4*1 = 4
2*.5 = 1
8*2 = 16 coulombs
Q = i t
so
t = Q/i
t = 2.5 /5*10^3 = (1/2) * 10^3
= 500 seconds 
The answer is D