Kirchhoff's Laws and current through resistors

[Vashti]

Question:

The diagram below shows a circuit where; R1 = 5.00 Ω, R2 = 6.00 Ω, R3 = 1.00 Ω, V1 = 4.500 V, V2 = 20.00 V, and V3 = 6.00 V. (In solving the problems that follow, initially pick the current directions as shown. If the actual current turns out to be in the opposite direction, then your answer will be negative).
What is the value of I1? I2? I3?

Attempts:

So I know that I need three equations to solve it as I have three unknowns. I tried to make one using the junction where I2 meets I1 and I3, but they all come together and kind of crash, so I don't know how to put that into equation form any more :( I'm assuming I need to do loops to get the other two equations but again I run into the issue of knowing how to set them up. If I try to make points on either side of each resistor they won't 'flow' really...
In summary I am just very confused, so any help is welcome!

Thanks!

 

[Astronuc]

There are two loop equations for the voltages around each loop, and there is one current equation.

Sum if currents (net) into a node is zero, so I1+I2+I3=0, because what goes in must come out, otherwise there is a net charge accumulation. If all current arrows go into a node, then one must be negative, i.e. the current is opposite the arrow.

 

[Moetasim]

Hi there,

It seems like you are on the right track with using Kirchhoff's Laws to solve this circuit. To set up the equations, you can use Kirchhoff's Current Law (KCL) at the junction where I2 meets I1 and I3. This law states that the sum of the currents entering a junction must equal the sum of the currents leaving the junction. So for this junction, the equation would be:

I2 + I3 = I1

To get the other two equations, you can use Kirchhoff's Voltage Law (KVL) around each loop in the circuit. This law states that the sum of the voltage drops around a closed loop must equal the sum of the voltage rises. So for the first loop, using the current direction shown, the equation would be:

V1 - R1*I1 - V2 = 0

And for the second loop, the equation would be:

V2 - V3 - R2*I2 - R3*I3 = 0

From here, you can solve the system of equations to find the values of I1, I2, and I3. Remember that if the actual current turns out to be in the opposite direction, your answer will be negative, so be sure to check your final values.

I hope this helps! Let me know if you have any other questions or if you need further clarification. Good luck!