Circuit analysis

[windozeuser]

Hello board, I ran into a relatively (well I thought) simple problem, but I think I'm going brain dead.

**broken link removed**

The above circuit has a 100 ohm, and a 70 ohm(68 was closest) resistor in series with a resistor(Rx) in parallel across points A and B. There must be 3V at points A and B.

using ohms law

The series resistors must drop 17 volts

I = 17V/170ohms
I = 0.1 (100mA)

so Rx = 3/0.1 = 30 ohms?

Am I correct, please help

Thanks

 

[audioguru]

You are correct as long as nothing is in parallel with the 30 ohm resistor.

 

[Comcat]

Rx is not in parallel.
Rx is in series with the 100 ohm and the 68 ohm. You are correct that setting the value of Rx at 30 ohms will result in 3 volts across Rx.

 

[ljcox]

Yes.

You can cross check by calculating the voltage across the 30 Ohm res.

V = 20 * 30/(30 + 170) = 20*30/200 = 3 Volt

QED.

By the way, Rx is not in parallel with anything. It is connected between points A & B.

 

[windozeuser]

Thank you all for your help, yeah I don't know what I was thinking, Just one of those days ;P

 

[ljcox]

You're welcome. We all have days like that.