Current Electricity — Physics STD 12 Science — Question

The chief sources of error in the meter bridge experiment are as follows:
1.The cross-section of the bridge wire may not be uniform. The wire's resistance will not be proportional to its length since it will not have a consistent resistance per unit length.
2.End resistances at the wire's two ends may be introduced as a result of
(a) the resistance of the metal strips
(b) the contact resistance of the bridge wire with the metal strips
(c) unmeasured lengths of the wire at the ends because the contact points of the wire with the metal strips do not coincide with the two ends of the metre scale attached.
Such errors are almost unavoidable but can be minimized considerably as follows:
1.Readings must be taken by modifying the standard known resistance to obtain the null point close to the wire's centre. The null points should be in the middle one-third of the wire when taking multiple readings.
2.The measurements must be repeated with the standard resistance (resistance box) and the unknown resistance swapped in the gaps of the bridge, and the averages of the two results obtained.