Calculating the Thévenin Voltage (Vt) and Thévenin Resistance (Rt) equivalent of the circuit below
Thevenin Voltage


  The Thevenin voltage e used in Thevenin's Theorem is an ideal voltage source equal to the open circuit voltage at the terminals.


The 2 Ohm resistor is "open" and the 4 and 6 Ohm resistors form a voltage divider, therefore:

Vt = (50V * 6 Ohm) / ( 4 Ohm + 6 Ohm) =

300 / 10 = 30V

Explanation: The voltage at the node between the 3 resistors is the same proportion between the 6 Ohm resistor (which is the one attached to 0V) and the total resistance presented by the voltage divider (6 + 4 Ohm), so 6/10, 60%. 60% of 50V = 30V.

This can be better visualized this way:







simulate this circuit &ndash; Schematic created using CircuitLab

Thevenin Resistance


  The Thevenin resistance r used in Thevenin's Theorem is the resistance measured at terminals AB with all voltage sources replaced by short circuits and all current sources replaced by open circuits.


So:

Rt = 

(6 Ohm in parallel with 4 Ohm) + 2 Ohm = 

(6 * 4)/(6 + 4) + 2 = 24/10 + 2 = 4.4 Ohm

This can be better visualized this way:







simulate this circuit

Therefore:







simulate this circuit

All the info I used can be found here. The calculator on the website gives the same results.