Question

Which Kind of material is used for meter bridge wire and explain why?

Answer 1

A meter bridge consists of one meter wire which is based upon the principle of Wheatstone bridge and it’s used in determining the unknown resistance of a conductor as we used in Wheatstone bridge by balancing the opposite parallel ends such that no current flows through the middle wire.

Complete answer:
Firstly, we need to know the concept of Wheatstone bridge. A Wheatstone bridge consists of four resistance which are placed at opposite parallel ends and balanced by a middle wire when no current flows through this wire, we can easily calculate the unknown resistance of given material. By balancing all four given resistances. This same principle is used in meter bridge wire.

Meter Bridge is a simple wooden formed instrument which has a straight wire fixed across both ends whose length is of one meter and this wire has a uniform cross-sectional area in its whole length. The wire which is used in Meter Bridge must have these properties:
-Wire must have high specific resistance.
-Low temperature coefficient of resistance.

High resistance wire is used because if resistance is very high then current will be very low.Hence the galvanometer needs to be very sensitive to the low current otherwise you will get zero reading even if there is current flowing in wire and the Meter Bridge will be unbalanced. Low temperature coefficient of resistance makes the resistance of wire unchanged with increase in temperature of wire due to flow of current.

Hence, Alloys constantan and NiChrome which satisfy these two specific properties are used in making meter bridge wire.

Note: An alloy is a combined mixture of some metals, or a metal when combined with one or some more other elements. Alloy NiChrome is very resistant to corrosion and it has a very high melting point around ${1400^ \circ }C$which makes it highly popular in making meter bridge wire.