Thevenin’s theorem

 Thevenin’s theorem  :                  

 In electrical circuit theory, Thevenin’s theorem for linear electrical networks states that any combination of voltage sources, current sources and resistors with two terminals is electrically equivalent to a single voltage source V and a single series resistor R. For single frequency AC systems, the theorem can also be applied to general impedances, not just resistors.Any complex netwok can be reduced to a Thevenin's equivalent circuit consist of a single voltage source and series resistance connected to a load.

Through the use of Thevevnin’s Theorem, we have the ability to reduce to a complex circuit down to simple series circuit:

1. Remove the components of interest- normally called load. ( Mark the terminals where the load was removed from)

2. Determine the voltage seen by the load , called thevenin’s voltage V_th.
3. Replace the voltage source by a short circuit open circuit the current source.
4. Determine the resistance seen by the load, called Thevevnin’s resistance R_th.

              Thevenin’s theorem Video Class room by YOU TUBE.

Example:   Find I_L by Thevenin’s theorem (Fig-1)

From Fig -2   we get,

V_AE =  10/(3+2)  * 3 

          = 6v

V_BE = 4/(3+1) * 3

         = 3v

So,   V_AB  =  V_th  =  V_AE + V_BE    =  6v + 3v  =  9v

From   Fig- 3 we get,   

      R_AB  =   R_th  = ( 2*3)/(2+3)  + (3*1)/(3+1) 

                          =  1.2 + 0.75  =  1.9Ω

From Fig-4  we get,   I_L   =  9/(1.9+10)

                                                   =  0.75 Amp  (Ans)