Solve KCL/MESH Problem: E=15V, R1=20k, R2=4.7k, R3=10k

[thorwynn]

Homework Statement

Determine I_1 I_2 I_3
When
E = 15V
R1 = 20k ohms
R2 = 4.7k ohms
R3 = 10k ohms

Homework Equations

KCL equation

The Attempt at a Solution

i tried to find using KCL.. is my equation right?
Loop equation 1:
EB + I3R3 + R1(I3 + I1) = 0

Loop equation 2:
R1(I1 + I3) + R2(I1 – I2) = 0

Loop equation 3:
EB + I3R3 + I2R2 = 0

can i use MESH analysis... but there are three unknowns and if i use mesh, i can only have 2 equations with 3 unknowns

 

[Redbelly98]

Welcome to PF.

There is a problem with your equations.

The voltage across R1 is is simply R1*I1, not R1(I1 + I3), because the current flowing through R1 is simply I1.

Likewise, the voltage across R2 is R2*I2.

Also, these are KVL equations for voltage, not KCL which would apply to currents. KCL says that the sum of all currents entering a node is zero, and will be useful here.

Note, another way to solve this would be to use the rules for combining resistors in parallel and series.

 

[noumed]

I agree with Redbelly98, I think you're confusing KVL for KCL. See if you can combine the resistors to find the current coming out of the supply. From there, I think it's easier if you find the http://en.wikipedia.org/wiki/Norton_equivalent" equations. See link for quick wikipedia articles on them. Mesh analysis will work just fine here as well, but I think it's more obvious using Norton equivalent.

 

[memo50]

u can apply kvl at the 2mishes and get 2equa., in 2variables .then solve them