Gce Model Questions Vol1 2024 Physics Question 49

Three long parallel wires A, B and C are separated as follows: the distance between A and B is \(d_{AB}=0.04\,\text{m}\) and between B and C is \(d_{BC}=0.06\,\text{m}\). Each wire is 10 m long and has a resistance per unit length of \(0.5\,\Omega\,\text{m}^{-1}\). Wires A and C are directly connected across a 120 V supply, while wire B is also connected directly across the same supply. All currents flow to the right. (i) Find the smallest integer number of turns \(N\) (10 ≤ N ≤ 100) that can be added to wire A (as an extra series resistor) so that the net magnetic force per unit length on wire B due to wires A and C is zero. (ii) Calculate the total electrical power dissipated in the three wires (including the added resistor on A).