Question

Coils in the resistance boxes are made from doubled up insulated wires(a) to cancel the effect of self induction(b) to nullify the heating effect(c) to nullify the Peltier effect(d) to reduce effective length of the wire

Answer 1

to reduce effective length of the wire is your answer to the question

Answer 2

Answer:

Explanation:

The wire is doubled back on itself. As a result ,there are equal and opposite currents in each section of the coil. Therefore ,the coil has no net magnetic field and no net induced e.m.f.

Thus, it is done to minimize the inductance of coils.