State any two sources of error in meter bridge experiment. Explain how they can be minimised.

Answer: (1) End resistance/contact resistance at the ends of the wire — minimised by interchanging the two resistances and taking the mean, and by keeping the null point near the middle. (2) Non-uniform cross-section of the wire — minimised by using a uniform wire and taking readings with the null point near the centre.

1. End resistances: the copper strips and the joints at the ends of the wire add small unknown resistances, and the zero and 100 cm marks may not coincide with the actual ends of the wire. Minimised by choosing the known resistance so that the null point lies close to the middle (about 50 cm), and by interchanging \(X\) and \(R\) and taking the mean of the two results (this cancels end corrections).
2. Non-uniformity of the wire: the wire may not have the same cross-section (and so the same resistance per cm) everywhere. Minimised by using a wire of uniform area and material and by taking several readings with the null point near the middle and averaging them.

Also, the current should be passed only while taking readings, so that the wire does not heat up and change its resistance.