In a meter bridge experiment resistances are connected as shown in the figure. Initially resistance P = 4 W and the neutral point N is at 60 cm from A. Now an unknown resistance R is connected in series to P and the new position of the neutral point is at 80 cm from A. The value of unknown resistance R is :

In balance position of bridge, P Q (100 ) = – l l Initially neutral position is 60 cm. from A, so 4 Q 16 8 Q 60 40 6 3 = Þ= =W Now, when unknown resistance R is connected in series to P, neutral point is 80 cm from A then, 4R Q 80 20 + = 4R 8 80 60 + = 64 64 24 40 R 4 6 66 – = -= = W