# find the charge q(t) flowing thru a device if the current is:

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• Dec 22nd 2010, 02:37 PM
bigwave
find the charge q(t) flowing thru a device if the current is:
$A=$Amperage $C=$Coulombs

$i(t)= 3A$, $q(0) = 1C$

The Ans is $3t+1$

this is very new subject to me but I assume we want to use

$
Q \triangleq \int_{t_0}^t i \ dt
$
• Dec 22nd 2010, 03:07 PM
Archie Meade
Quote:

Originally Posted by bigwave
$A=$Amperage $C=$Coulombs

$i(t)= 3A$, $q(0) = 1C$

The Ans is $3t+1$

this is very new subject to me but I assume we want to use

$
Q \triangleq \int_{t_0}^t i \ dt
$

Yes,

$\displaystyle\ i=\frac{dQ}{dt}\Rightarrow\ Q=\int{i}dt$

$\displaystyle\int{i}dt=Q=it+q(0)$

where $q(0)$ is the initial charge.
• Dec 22nd 2010, 03:20 PM
bigwave
then we just plug
so for

$\int{i}dt=Q=it+q(0)$

then we just plug in $3$ into $it$ and $1C$ into the q(0)

to get the $3t + 1C$
• Dec 22nd 2010, 03:37 PM
Archie Meade
Yes, that's all that's required Bigwave.
A constant current of 3 Amps will cause the passing charge through the device to ramp up linearly with time.
• Dec 22nd 2010, 03:57 PM
bigwave
I'll be posting a lot more EE stuff if you are up for it.... brave new world for me...
• Dec 22nd 2010, 04:10 PM
Archie Meade
Ok Bigwave!
I will keep an eye out for those.
(Cool)