# Kirchoff's voltage law applied to this circuit with three loops

• Engineering
Homework Statement:
Determine the loop currents i1 to i4 in the electrical network shown
Relevant Equations:
I in = I out V = IR
I'm stuck straight out of the gate any help is really appreciated

#### Attachments

• Kirchoff.png
14.8 KB · Views: 53

## Answers and Replies

berkeman
Mentor
Homework Statement:: Determine the loop currents i1 to i4 in the electrical network shown
Relevant Equations:: I in = I out V = IR

I'm stuck straight out of the gate any help is really appreciated
Welcome to PhysicsForums. We are not allowed to help you until you show your best efforts to work the problem.

Start by listing the KVL equations for each loop. They say how you would go about solving those simultaneous equations...

• Doomkey
Oh sorry I'm quite new so didn't know the rules, thank you for replying

70i1-50i2-30i3=240v for the i1 loop
100i2-50i1-25i4-10i3=240v for the i2 loop
65i3-10i2-30i1-20i4=240v for the i3 loop
50i4-25i2-20i3=240v for the i4 loop

my problem is I'm not confident I'm making the simultaneous equations correctly, but if I am then I can simply fiddle around with them until I get a result for one of the loops then plug that back into the other equtions and work from there

gneill
Mentor
I see a 240 V potential source in only one loop. You seem to have it in all the loop equations.

Check the resistor sum for i4 in your final equation.

edit: Also check the resistor sum for i1 in your first equations! What's 50 + 30?

• Doomkey
100i4-25i2-30i3 for the i4 loop, I was making the three resistors in series into one resistor but realized my mistake. I thought the PD for the whole circuit would be 240V and as they're all in parallel shouldn't they all have the same PD?

gneill
Mentor
I thought the PD for the whole circuit would be 240V and as they're all in parallel shouldn't they all have the same PD?
Nope. The 120 V potentials are only at the top nodes of the diagram. After that there are resistors in the way, so potential drops due to current flows.

• Doomkey
How would I go about calculating how much potential is in each loop? sorry if I'm asking obvious questions but circuits are my weakest subject and having two nodes at the top not connected to each other is something I've never come across

gneill
Mentor
You calculate potentials in a circuit by solving the circuit equations. Once you know the currents, you can calculate the potential across any component via the net current passing through it. Ohm's law!