Thevenin's theorem states that any linear circuit with voltage and current sources can be simplified to an equivalent circuit with a single voltage source and a single series resistor.
To find the Thevenin equivalent, you need to remove the load resistor and calculate the open circuit voltage across the load terminals. Then, calculate the equivalent resistance by shorting all voltage sources and opening all current sources in the original circuit. The Thevenin voltage is the open circuit voltage and the Thevenin resistance is the equivalent resistance.
The 6 Ohm resistor represents the equivalent resistance of the original circuit when all voltage sources are shorted and all current sources are opened. It is necessary for calculating the Thevenin equivalent voltage.
The Thevenin equivalent allows us to simplify complex circuits into a single voltage source and a single resistance, making it easier to analyze and design circuits. It also helps in determining the maximum power that can be delivered to a load.
No, Thevenin's theorem only applies to linear circuits. Non-linear circuits have different characteristics and cannot be simplified to a single voltage source and resistance.