# using nodal analysis to find i4

#### hunterage2000

Joined May 2, 2010
487
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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#### t_n_k

Joined Mar 6, 2009
5,455
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.

#### renotenz

Joined Oct 25, 2010
11
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

#### thatoneguy

Joined Feb 19, 2009
6,359
The post above is the correct answer, 2 unknowns, 2 equations.

<erased a buncha typing>