Current flow in a two source circuit

[xJJx]

Hi guys, is the current flow in this picture correct? I'm trying to understand current flow in a two source circuit.

 

[berkeman]

Can you post a better version of your picture? Take it without any shadows over the paper, and rotate and process it a bit to make it easy to read.

 

[xJJx]

Here's a better picture

 

[berkeman]

Thanks. The circuit might be okay, but how are you setting the current of the left voltage source to 5A? What are the values of the resistances?

 

[xJJx]

Thanks. The circuit might be okay, but how are you setting the current of the left voltage source to 5A? What are the values of the resistances?

Hi, thanks for your reply :) The question doesn't tell me the resistance values, it just tells me everything stated on the picture. I thought current travels from positive terminals to negative, so I guessed the current flow directions to be like this ^. Is this correct?

 

[cnh1995]

so I guessed the current flow directions to be like this ^. Is this correct?

Partly.

Pink current doesn't flow in the right loop and green current doesn't flow in the left loop.

 

[xJJx]

Partly.

Pink current doesn't flow in the right loop and green current doesn't flow in the left loop.

haha I read that in Sheldon's voice & please may you explain why?

 

[phinds]

haha I read that in Sheldon's voice & please may you explain why?

When you define loop current they should be confined to individual loops. This doesn't mean part of each current doesn't flow in the other loop but you can't solve for values without specific loop currents.

 

[cnh1995]

haha I read that in Sheldon's voice & please may you explain why?

You have 5A flowing from the battery (pink) and 6A through the middle resistor. So, the remaining 1A (green) must be supplied by the rightmost current source. Hence, both 5A and 1A are confined to their respective loops. They add up in the middle branch and again split at the bottom node such that the pink current flows back to the battery and the green current flows back to the current source.

 

[xJJx]

You have 5A flowing from the battery (pink) and 6A through the middle resistor. So, the remaining 1A (green) must be supplied by the rightmost current source. Hence, both 5A and 1A are confined to their respective loops. They add up in the middle branch and again split at the bottom node such that the pink current flows back to the battery and the green current flows back to the current source.

But even if the two currents are confined to their respective loops, that still doesn't mean part of them can't flow in the other loops. So I still don't understand why they don't split at the bottom junction.

 

[phinds]

But even if the two currents are confined to their respective loops, that still doesn't mean part of them can't flow in the other loops.

Yes, that's exactly what I said in post #8

So I still don't understand why they don't split at the bottom junction.

You PRETEND that they are totally separate currents so that you can solve for them, Again, this is what I already explained in post #8. What is it about that that is not clear? How would YOU solve for values if you mix everything up the way you seem to want to? Do you understand how to solve current loops?

 

[xJJx]

Yes, that's exactly what I said in post #8

You PRETEND that they are totally separate currents so that you can solve for them, Again, this is what I already explained in post #8. What is it about that that is not clear? How would YOU solve for values if you mix everything up the way you seem to want to? Do you understand how to solve current loops?

No, I haven't learned how to solve current loops. I haven't started university yet, I'm trying to learn this stuff before uni starts. I know how current flows in a single-source circuit, but not in a two-source circuit.

 

[xJJx]

Yes, that's exactly what I said in post #8

You PRETEND that they are totally separate currents so that you can solve for them, Again, this is what I already explained in post #8. What is it about that that is not clear? How would YOU solve for values if you mix everything up the way you seem to want to? Do you understand how to solve current loops?

Is the 'currents confined to their respective loops' thing just an assumption we make for determining the loop currents in the circuit? do we ALWAYS make this assumption for two-source circuits, even when we're not trying to determine loop currents?

 

[phinds]

Is the 'currents confined to their respective loops' thing just an assumption we make for determining the loop currents in the circuit? do we ALWAYS make this assumption for two-source circuits, even when we're not trying to determine loop currents?

The number of sources is irrelevant and the number of loops is irrelevant. You draw a single current around each loop, write the resulting equations, and solve. Elements that are common to two loops have a current which is the sum/difference of the two loop currents. Assumed direction of the loop currents is irrelevant. If you've made the "wrong" assumption you just get a negative answer.