Meter Bridge

In a meter bridge a resistance of R Ω  and a shunt resistance S Ω are connected as shown, the null point is found to be at 40cm from A If a 12 Ω resistor is connected in parallel with S the null point changes to 50cm Find R and S.

1^st case

R / 40=S / 60

R=2S/3 --------------- (1)

2^nd case

R / 50= [12S / (12+S)] / 50      (12 Ω and S Ω are connected in parallel )

 ie R=12S / (12+S) ---------------(2)

solving (1) and (2)

S=6 Ω and R=4 Ω