What is the electric potential V at a distance r from a point charge Q? Write down an expression describing the electric potential due to a continuous charge distribution. Consider a disk of radius R which carries a uniform surface charge distribution. (a) Find the total charge on the disc. (b) Find the potential at a point on the axis of the disc lying at a distance x from the disc. (c) What is the form of the potential when x becomes much larger than R? Comment on your result.