First quiz says, a one millimeter, cross section of copper wire.

Is isolated in 50 C of charge flow through it in two seconds.

How much current flow through the wire, in that time?

So let's solve this.

We know that the current in this case is charge over time,

or 50 C of time in two seconds, which is 25 amps of current.

The second quiz says, for

that same one millimeter cross section of wire that's isolated,

the charge that flows through the cross section is a function now Q(t)=4t^2+5.

How much current flow through the wire in 6 seconds?

So now in this case, I is a function of time,

so we need to differentiate Q,

with respect to time, to get 8t and at six seconds,

our current is eight times six, or 48 amps.

Now current can actually flow in any direction depending

on the source we're using.

So what are the reference directions for current flow?

You see here, two pieces of material, and

in one of the pieces current is flowing from the + to the -,

and in the other the current is flowing from the- to the +.