tranforming parts of a circuit

[transgalactic]

in this circuit:

https://i45.tinypic.com/29vctiv.jpg
they change a current source into a voltage source


i dont know what are the rules of doing this thing
how they did it
??

 

[sfink06]

google source transformation. Basically a voltage source in series with an impedance can be represented as a current source in paralel with the same impedance.

 

[sfink06]

and vice versa

 

[transgalactic]

ok i have two more questions about this circuit regarding northon/thevenin stuff

we dont have any independent sources in this circuit
so we add a 1v source (as you see in the solution)
1.why did they transformed the source
why cant we find the northon /thevenin with circuit looking like this
?
2.
why they write the voltage source as <- +>

the current souce looked like this < -> >
so the voltage drops from left to right
we got a higher potential on the left and a lower one on the right
so it should be looked like <+ ->

where is my mistake?

 

[sfink06]

Take a look at the wikipedia article. As for why they did it, it just makes the KVL equations easier to set up. They did it the right way, I think you are counfused by looking at the load. Notice that the sources are polarized the same way? That's what you want.

 

[transgalactic]

the current flow from high potential to low potential.
so if it flows form left to right
then we have a high potential on the left and low potential on the right.

so the plus of the buttery needs to be on the left and minus on the right

but the got it other wise
why?

and this issue is not disscused in this article
https://en.wikipedia.org/wiki/Source_transformation

 

[sfink06]

Current flows from high to low in a resistor, but in a battery that's producing power it goes grow low to high.

 

[transgalactic]

ok i understand this part

but look in this branch
they signed I1 and I2 going in different directions
why??

its supposed to be only I2
only one currect flow in one wire

another question about it is ,why did they transformed the source
why cant we find the northon /thevenin with circuit looking like this
?

 

[sfink06]

I1 is nothing but -I2. Remember that current can only flow one way, so only one direction is correct.

 

[transgalactic]

why did they transformed the source
why cant we find the northon /thevenin with circuit looking like this
?

 

[pedroromanvr]

Yeah, the circuit can be solved in the two forms, and it must have the same answer. So they made source transformation to avoid obtain 4 equations to solve, instead of 3. You can try solving these the other way and compare answers.