Problem 3 Consider a rod of copper 15cm long with a coating of nickel on one end that is 10m thick. Assume that the interdiffusivity of the copper and nickel can be described by a constant diffusion coefficient, D. Write an expression for the concentration of nickel in the copper rod as a function of position and time that is valid for distances more than 100m from the Ni coated end of the rod. Make sure to specify the coordinate system you use