# d.c circuits

• October 2nd 2013, 12:18 PM
Jock
d.c circuits
The circuit shows a 10kohm potentiometer with a 5kohm load. Determine the position of the slider on the "pot" when the voltage across the point "xx" is 3v? ImageShack® - Online Photo and Video Hosting
Any help greatly received as I am really struggling with this. Thanks
• October 2nd 2013, 08:57 PM
topsquark
Re: d.c circuits
Quote:

Originally Posted by Jock
The circuit shows a 10kohm potentiometer with a 5kohm load. Determine the position of the slider on the "pot" when the voltage across the point "xx" is 3v? ImageShack® - Online Photo and Video Hosting
Any help greatly received as I am really struggling with this. Thanks

You have two resistors in parallel, the 5 kOhm and R (from the potentiometer.) You know, then, there is a 3 V potential difference across the 5 kOhm resistor as well as 3 V across the R. You also know that the currents in a parallel circuit are additive. So....
$3 = I_1 \cdot 5$

$3 = I_2 R$

$9 = I R_{eq}$
where this last is for the circuit as a whole. (Recall $I = I_1 + I_2$)

Three equations, three unknowns...

-Dan