Question

Can we use copper wire instead of nichrome in meter bridges?

Answer 1

Hint: In order to understand the difference a copper wire would make in the functioning of meter bridge as compared to the nichrome, we need to first understand why is the nichrome wire used, and what are those special properties that these nichrome wires possess which make them suitable for the usage in the meter bridge.

Complete answer:
Meter bridge is a device that is used to calculate the resistance(which is unknown) of a conductor. In meter-bridge, the principle that is used is called a wheatstone bridge. Now, according to the requirement in the meter bridge, it is necessary that the connecting wire that is used in it should have a high resistance value and a low temperature coefficient of resistance. Temperature coefficient of resistance means the change in the value of resistance as we change the temperature.
Thus, with the given conditions of the connecting wire, it can be seen that only those elements can be used which have high resistance value and low temperature coefficient. The value of resistivity of nichrome wire is $1.10 \times {10^{ - 6}}\Omega m$, which when compared to copper wire whose resistivity value is $1.68 \times {10^{ - 8}}\Omega m$ , is around $100$ times more.
Thus, copper, due to its low resistance and high temperature coefficient of resistance, cannot be used in meter bridges.

Note:
It is not necessary to use only nichrome wire in all the construction of meter bridges as connecting wire. Any wire which has high resistance and low temperature coefficient of resistance will work as a connecting wire. Examples of elements which can be used as connecting wires are manganin and constantan.