# How to find the current in this circuit?

Please help me find the current flow in A1,A2 and A3. its my First FEE class and I was able to solve this with voltage source but with current source Iam Having trouble. also V1 and V3 are the voltages that also need to be found. any idea on this ? any help would be appreciated.

Spent the last 7 hours and tried all solutions best I know how with no luck getting the same values as the simulated results.

P.S I need to solve this manually. • First determine the resistance as seen by I1. – Peter Bennett Dec 16 '18 at 1:00
• It does sum up to 1.17kOhm If its the same way with voltage source. – Antonio Eljamous Dec 16 '18 at 1:03
• Knowing that resistance and the current should allow you to solve the problem. Since this is apparently a school assignment, I am trying to give you Helpful Hints, without actually solving it for you... – Peter Bennett Dec 16 '18 at 1:06
• So what's the voltage V3 (follows from the resistance). Then, what's A3? Given A3 how much current flows into R4? Then what's the drop across R4 and the voltage at V1? – John D Dec 16 '18 at 1:08
• It looks like a school assignment to me as well. Please try to show the calculations you have done so that we can point out your mistakes rather than showing the whole process. – JuneStar_2918 Dec 16 '18 at 2:29

One way to do this systematically is to write some equations in terms of mesh currents. I1 flows in the right hand mesh in an anticlockwise direction and acts upon R3. I2 flows anticlockwise in the central mesh and acts upon R2, R3 and R4. Finally I3 flows in the left hand mesh and acts upon R2 and R2. I1 and I2 are unknown. The next step is to write an equation based on the fact that the sum of voltages around the left hand mesh must equal zero. Same for central mesh. You are left with 2 simultaneous equations with 2 unknowns so you can solve for I1 and I2.

The equivalent resistance beyond the resistor R4 (i am coming from right to left on the circuit)is:

R(1||2)=(1k*4k)/5K=800Ohm.

This gives you the following reduced circuit: simulate this circuit – Schematic created using CircuitLab

Now the current through the R3 can be determined by applying current divider rule(consider going through this topic once) as:

A3=[R4+R(1||2)]*I1/[R3+{R4+R(1||2)}].

You can find the current A3 to be 0.58mA.

Look at the question now and forget the reduced schematic. The remaining 0.42mA current passes through R4 and it divides itself for R2 and R1. Apply current divider rule here as well:

A2=R1*0.42/(R1+R2)=0.084mA.

Now the remaining of 0.336mA(=A1) current flows towards R1. Here you need to take negative of this current because the direction specified in the question is opposite to the direction it actually flows.

For the voltage V3, apply Ohm's Law. I will show you the solution of V3 and remaining one for you.

V3=A3*R3=0.58m*2k=1.16V.

• You're welcome@Antonio Eljamous – JuneStar_2918 Dec 17 '18 at 1:24