A "frozen-in" uniform polarisation density P exists in a very large block of dielectric with a cubic hole in the middle. The cube is oriented such that P is parallel to one its edges. There are no free charges. (a) Write down an expression for the bound charge density on the surfaces of the cubic hole. (b) Using the results of part (a) or otherwise, find the electric field at the centre of the cubic hole. nation: x = -b = -b b (x + y + b)-3/2 dxdy = 4