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# Kirchoff's law question watch

1. Hello all I am having a hard time working through this question. It wasn't explained in class and all the examples on YouTube show the second power supply in the middle of the circuit which I think has a different way of calculating the current. Was wondering if anyone could please explain and go through this clearly? Thank you.
https://imgur.com/a/sJHdW
2. If you consider each branch of the circuit as a different loop with the power supply and use Kirchhoff's second law and write an equation for each, then you can use Kirchhoff's first law at each junction to write equations for the currents. This might help you to see what's going on more clearly. Just remember V = IR in its various forms. Hopefully that gives you somewhere to start with it.
3. I can't solve this. :\

Can you / anyone else?
4. (Original post by Joxh)
Hello all I am having a hard time working through this question. It wasn't explained in class and all the examples on YouTube show the second power supply in the middle of the circuit which I think has a different way of calculating the current. Was wondering if anyone could please explain and go through this clearly? Thank you.
https://imgur.com/a/sJHdW
OP, I believe this is a node analysis question, with an independant voltage source.

For part a) firsty, define your reference node, which will be considered to have 0 Voltage.

Secondly, assign Node voltages V1, V2, and V3 to all the nodes other than the reference nodes. V1 and V2 are already labelled and given to you (the voltage supplies).

Thirdly, at any known node where voltage is fixed by an ideal voltage source, the corresponding node voltage may be written down at once.

After you apply these steps you can assign current to all branches, then apply Ohm's Law to all branches ( use Kirchhoff's Current law to relate these currents). Lastly, solve the unknowns using simultaneous equations ( in this example it just so works to simply substitute known values and rearrange algebraically to find one unknown value though).

Now for part b) all you have to do is use the formula P= V^2 / R

This is what I got:
5. I'm actually confused. I thought power sources in parallel just increased current but operated at the max voltage? And why in your diagram is there opposing flow from your node?

Sorry I hated electronics and I sort of didn't bother learning it ... .eeeeek
6. I ended up solving it and got I3 to be around 700mA. And the power dissipated by the resistor was 5.04W My teacher has my work now and he's given me the merit 😊
(Original post by shameful_burrito)
OP, I believe this is a node analysis question, with an independant voltage source.

For part a) firsty, define your reference node, which will be considered to have 0 Voltage.

Secondly, assign Node voltages V1, V2, and V3 to all the nodes other than the reference nodes. V1 and V2 are already labelled and given to you (the voltage supplies).

Thirdly, at any known node where voltage is fixed by an ideal voltage source, the corresponding node voltage may be written down at once.

After you apply these steps you can assign current to all branches, then apply Ohm's Law to all branches ( use Kirchhoff's Current law to relate these currents). Lastly, solve the unknowns using simultaneous equations ( in this example it just so works to simply substitute known values and rearrange algebraically to find one unknown value though).

Now for part b) all you have to do is use the formula P= V^2 / R

This is what I got:
7. (Original post by Joxh)
I ended up solving it and got I3 to be around 700mA. And the power dissipated by the resistor was 5.04W My teacher has my work now and he's given me the merit 😊

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