# using nodal analysis to find i4

Discussion in 'Homework Help' started by hunterage2000, Nov 19, 2010.

1. ### hunterage2000 Thread Starter Active Member

May 2, 2010
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How would I find i4 in the attached circuit using nodal analysis?

would I need to find the value of i3 first?

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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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For the purpose of simplifying the solution you would probably treat R3 & R4 as being an effective parallel equivalent - since they are in parallel. You would then find the node voltage at their topmost point of common connection. The current in R4 would simply be the node voltage value divided by the R4 value.

3. ### renotenz New Member

Oct 25, 2010
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0
Well, instead of paralleling R3 and R4 first, I prefer just to find the voltage on right node first.

Let's assume that the node on the left of R2 is Node A and the node on the right of R2 is Node B. Yep, just two nodes needed. Node A voltage is Va and node B voltage is Vb

Node A :

i1 = Va/R1 + (Va-Vb)/R2 ...(1)

Node B :

0 = (Vb-Va)/R2 + Vb/R3 + Vb/R4 + (Vb-V1)/R5 ...(2)

Simplify those two equations, just use eliminination or substitution method to find Vb.

Then you can find i4 which is Vb/R4. Cheers

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
The post above is the correct answer, 2 unknowns, 2 equations.

<erased a buncha typing>