# Superposition Theorem Prob #1

Discussion in 'Homework Help' started by J.live, Oct 9, 2010.

1. ### J.live Thread Starter Member

Sep 10, 2010
35
1
Have to find Ix.

Attempt:

Solving for current source:

I'x= 3.5 v / 7+3 + 15 ll 5 ?

the solution manual did not consider 5 ohms at all , instead

I'x= 3.5 v / 7+3+15

I don't understand why.

Solving for voltage source:

I''x= 2 x ( 10 / 10 + 15)

According to the manual 5 ohms is zero since it is parallel to the short circuit ( 3.5 v).

Isn't 5 ohms also parallel to 10 ohms ( 7+3) ?

Any help will be appreciated.

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2. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
104
Because 5Ω is in parallel to a perfect voltage source. You can have many resistors in parallel to the voltage source and you can do the trick as I did in the image.

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3. ### J.live Thread Starter Member

Sep 10, 2010
35
1
Considering the current source. When a resistance is put in parallel with a short circuit, the total resitance of the branch falls to zero. This can be found either by the formula $R_t=\frac{R \cdot 0}{R + 0}=0$ or intuitively, by thinking that the current will choose the "easiest" path to go, the one that will have no resistance. This analysis leaves us with two parallel branches, one with 10Ω and one with 15Ω, led by a source of 2Amps. You can work the rest of the math yourself.