# Homework Help: Superposition Theorem

1. Sep 7, 2010

### frostchaos123

1. The problem statement, all variables and given/known data

Hi all

I have been struggling to find the right ans for the I(R1) in this circuit.

First i consider only the voltage source by opening the current source. As such i find that I'(R1) = (4-0.7)/1K = 3.3mA

Secondly i consider the current source by shorting the voltage source. Thus i derive I''(R1) = 3mA

Finally i get I(R1) = I'(R1) + I''(R1) = 3.3m + 3m = 6.3mA

However the ans seems to indicate as only 3.3mA.

Thanks.
[PLAIN]http://img823.imageshack.us/img823/8508/circuit.png [Broken]

Last edited by a moderator: May 4, 2017
2. Sep 7, 2010

### vela

Staff Emeritus
You've neglected the 20-ohm resistor completely. Try recalculating everything taking it into account.

3. Sep 7, 2010

### mplayer

When you shorted the voltage source, I think you assumed you could combine the two voltage sources together like you did in the first part of the calculation, but you cant. Try calculating the current through R1 just one source at a time - the current source, V1, then V2.