MEASUREMENT OF MEDIUM RESISTANCE BY WHEATSTONE BRIDGE METHOD.

 

MEASUREMENT OF MEDIUM RESISTANCE BY WHEATSTONE BRIDGE METHOD.

WHEATSTONE BRIDGE

Wheatstone bridge is also known as Resistance Bridge, Calculate the unknown resistance by balancing two legs of the bridge circuit, one legs includes the component of one resistance.  he is the best and the commonest method of measuring medium resistances and measures resistances with a good degree of accuracy. It works on the principle of Null reflection, Which mean the ratio of the Resistance’s are equal and hence, low current flows to the galvanometer or circuit under normal condition. The bridge circuit will be in unbalanced condition where the current flows through to the galvanometer. The bridge will be in the balanced condition when  no current flows through the galvanometer.

Since, The above diagram shows, The total current is divided into two parts I₁ and I₂, arm AB and AC are parallel to each other Therefore voltage must be equal.

Therefore, accordingly ohm’s law,       

 I₁p=I₂R    -------------------------(1)

At balanced condition no current flows through the galvanometer.

Therefore, Arm BC is open circuit.

                  _O^O_O                  I₁=I₃        and        I₂=I₄

Accordingly to ohm’s law                           

     -------------------------(2)                                                       

     -------------------------(3)

Combining equation 1, 2 and 3 and simplify

From equation 1,

I₁P=I₂R      ;           

                           

  Therefore,       RQ = PS       or