Question

Appropriate material to be used in the construction of resistance boxes out of the following is:
A. Copper
B. Iron
C. Manganin
D. Aluminium

Answer 1

Hint: In this question, we need to comment on the material which is being used in the construction of the resistance boxes. For this, we will go through the properties of the material required to make resistances and try to relate the same with the given options.

Complete answer:
For a material to be suitable for making resistance boxes, the resistance of the material should not change with any factors. The main factor is temperature. Wires, resistors and other equipment get heated due to their resistance during the flow of current. Hence for accuracy of the resistance boxes, its resistance should not change with temperature.

However for metals and metallic alloys, the resistance changes with heating. More specifically, it increases due to heating. The change in resistance of metals depends upon a constant which depends on the material. This property or constant is named as temperature coefficient. The more the value of temperature coefficient, the more the resistance changes with temperature.

Thus for the best material for resistance boxes, the material should have low temperature coefficient. Amongst all the materials given in the options, the temperature coefficient of manganin is the least. Manganin is an alloy of manganese, copper and nickel.

Hence, option C is the correct answer.

Additional Information:
Along with the temperature coefficient, the resistivity of the material should also be suitable. If the resistivity of the material is low, we would need a longer wire and a thinner wire to create the same resistance. The resistance box may not be handy due to the increase in its size.

Note: It is interesting to note here that an ideal resistance of a substance should not change with any factors like temperature, current or voltage. Moreover, the resistance box should be handy. Thus, a material with resistivity should be used.