Thevenin

Thread Starter

gbox

Joined Dec 29, 2015
42


I have found that I_1=3.81A and I_3=3.09A and I_2=0.72A and R_th=5.45Ω.
What do I need to do to find V_th?
 

Thread Starter

gbox

Joined Dec 29, 2015
42
so I need to calculate this loop:



But it is an open circuit, does the battery give voltage? does the 4\Omega resistor drop voltage?
 

crutschow

Joined Mar 14, 2008
24,084
so I need to calculate this loop:
----------------------
But it is an open circuit, does the battery give voltage? does the 4\Omega resistor drop voltage?
Yes, a battery has (gives) voltage, even when it is an open circuit.

The resistor will drop voltage only if there's current through it, i.e. if there's a load connected between A and B that draws current.
 
Last edited:

WBahn

Joined Mar 31, 2012
25,068
so I need to calculate this loop:


But it is an open circuit, does the battery give voltage? does the 4\Omega resistor drop voltage?
This diagram has I2 as the current flowing downward in the 2 Ω resistor. But in your original diagram I2 was defined as the current flowing to the right through the adjacent 4 Ω resistor (the one to the left). You need to be consistent in your use of variables.

A battery is a voltage source and a voltage source maintains a specified voltage across it regardless of the current through it -- including a current of zero.

A resistor drops voltage across it in direct proportion to the current flowing through it -- if there is no current through it, then there is no voltage across it.
 
Last edited:

WBahn

Joined Mar 31, 2012
25,068
Now, if the reason that you have I2 flowing downward in this diagram is because there is no current in the rightmost 4 Ω resistor and therefore I2 must also be the current flowing in the 2 Ω resistor, then that is correct and reasonable.
 
Top