Explanation
KCL :- It states that the sum of current meeting at any junction is equal to zero. Thus no charge has been accumulated at any junction.
KVL :- It states that the algebraic sum of changes in potential around any closed resistance loop must be zero i.e voltage drops are equal to voltage rises.
To increase range of ammeter, we need to decrease the resistance of ammeter. For this more shunt is added across ammeter.
Resistance in resistance box should be such that the null point is nearly in the middle of wire. In this position P, Q, R and S become nearly equal, and hence sensitivity of meter bridge will increase.
Since it is a balanced wheatstone bridge, no current flows through 10Ω resistance. Therfore by replacing 10 Ω by 20 Ω , current in circuit will be 4A
BC, CD and BA are known resistance . The unknown resistance is connected between A and D.
Resistance of metal increases on increasing the temperature ,so resistance of metal conductor in left arm will increase on heating .
R1 / R2 = l / 100- l
R1 increases on increasing l
Therefore, balancing poiont shifts towards right.
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