A high temperature fuel cell uses a cylindrical copper busbar of diameter d = 8mm to maintain electrical connection to a programmable load. The electrical connections at the load must be kept below 70C to avoid electrical fault, and the busbar emerges from a furnace which is maintained at 850C. The ambient temperature in the workshop is 25C.

a) Assuming the busbar is a cylindrical fin with a final busbar length of 2m (kcopper (at 390C) = 375 W.m-2.K-1), plot the temperature drop expected in the fin as a function of length (attach a print out of the graph and include all working).