Question

If the current in a wire of a cd player is 12.0 ma, how long would it take for 6.50 c of charge to pass a point in this wire? answer in units of s.

Answer 1

The current intensity is defined as the amount of charge Q that passes through a certain point of an electrical wire in a time interval of $\Delta t$:
$I= \frac{Q}{\Delta t}$

In our problem, the current intensity is
$I=12.0 mA=0.012 A$
while the amount of charge that passes a certain point of the wire is 
$Q=6.50 C$

If we re-arrange the previous equation:
$\Delta t= \frac{Q}{I}$
we can find the time needed for this amount of charge to pass through a point of the wire:
$\Delta t= \frac{6.50 C}{0.012 A} =541.7 s$