Simple (?) EE Question

[John Speth]

At 03:23 PM 2/7/97 -0400, you wrote:
>OK, so this is kind of a lame question - but I'm having a bit of trouble
>figuring it out. I wouldn't be surprised if many of you who took EE classes
>in college didn't see this question on an exam at one time or another.....
>
>Say you got a voltage divider, connected to V1, and Ground, R1 on top, R3
>on bottom.
>
>The voltage at the divider point is V1 * (R3/(R1+R3)). Fine.
>
>Now suppose you connect another resistor, R2, to the middle of the divider
>and connect it to voltage V2?
>What's the voltage at the divider point?
>
>More generally, if you have a star of resistors R1....Rn connected to
>voltages V1....Vn, is there a general formula for the voltage at the middle
>of the star?
>

My math (once through and no checking for mistakes) shows me that the
voltage at the divider point is:

V div = ((V2/R2) + (V1/R1))/G       where G = ((1/R1) + (1/R2) + (1/R3))

I think that you can see a pattern here and it can easily be extended to n
resistors.

John Speth (johns at oei.com)
Object Engineering, Inc.
Vancouver, WA