Kirchoff's Law Help (Electrical)

[Sinny]

I don't usually ask for help, but I'm quite stuck with this equation, for some reason even looking at guides is confusing me, can anyone help me?



I need to find I1, I2 and I3 (though I already know I3 will equal the former.

I've managed to get the following

4v=7A+5
2v=6B+5

but I know I'm wrong, any help appreciated, cheers

 

[W!ll]

Separate the two loops out as you have for A and B, arrange your equations for each above each other, substitute the voltages and resistances back in and solve the simultaneous equations.

EDIT: Without me drawing this out on paper for you please look at the link I've included, slides 10 and 11 show you the way to approach the problem in regards to forming the equations ignore the fact you have 2 resistors in loop A as due to the serial resistance rule they can simply be added.

https://iit.edu/arc/workshops/pdfs/Kirchhoff_s_Circuit_Laws.pdf

 

[Clarkson]

For each loop the sum of the voltage drops on the resistors will = the voltage source.

So for loop one it will look something like:

4V = I1*R1 + I1*R2 + I1*R3 + I2*R3
Therefore 4V = I1*(R1+R2+R3) + I2*R3
Therefore 4V = 7I1 + 5I2 (equation 1)

Loop 2:

2V = I2*R4 + I2*R3 + I1*R3
Therefore 2V = I2*(R3+R4) + I1*R3
Therefore 2V = 5I1 + 6I2 (equation 2)

Then you need to make either I1 or I2 the same for both loops by multiplying one or both of the equations to create (equation 3). Then subtract whichever equation you are looking at with (eq3).

This will result in I1 or I2 (depending which one you made the same value) cancelling out and leaving you nV = xI1 or xI2.

Then do the voltage figure divided by the xI1/xI2 figure and you will have the current (A) for either I1 or I2.

To find the other, simply substitute the current you know into the equation for the current you still need to find and voila.

(I have used some different notation but loop1 = loop A, loop2 = loop B, and the resistors (R) I have labelled as they appear in each loop going in the direction of conventional current flow).

 

[esoteric]

Been 14 years since I've had to do such things, I don't properly remember anymore

 

[Sinny]

Been 14 years since I've had to do such things, I don't properly remember anymore

I'm in my first 6 months of an apprenteship, having previously done Electrical Installation, I'm now working through Electrical engineering and it's way more harsh compared to my 2330.

Unsure whether to even try a HNC in 2 years haha!