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.
OOO I1=I3 and I2=I4
Accordingly to ohm’s law
Combining equation 1, 2 and 3 and
simplify
From equation 1,
I1P=I2R ;
Therefore, RQ = PS
or
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