Question

During an experiment with a metre bridge, the galvanometer shows
a null point when the jockey is pressed at 40.0 cm using a standard
resistance (R) of 90 , as shown in the fi gure. The least count of the scale
used in the metre bridge is 1 mm. The unknown resistance (X) is

Answer 1

Wheatstone meter bridge formula,

R2​R1​​=l2​l1​​

∴90R1​​=6040​

R1​=60Ω

Now,

we also have,

RdR​=L1​.L2​L1​+L2​​dL

60dR​=60.4060+40​0.1

∴dR=0.25Ω