Question

In an electrolytic cell the (-) electrode is negative because

Answer 1

The work of the electrodes in the electrolytic cell is to create a continuous current path through the cell - that means, electrons should be continuously flowing in and out. So you need two electrodes for it:

                  1) To supply/generate electrons

                  2) To take those electrons back

So, to achieve the first point (1), we use a negative electrode. The negative charge on it, repels the electrons (cuz electrons are negatively charged, you know) - thus electrons are pushed into the cell -- generation of electrons -- flowing IN.

To achieve the 2nd point, we need a positive electrode to attract those electrons  back. So electrons are removed from the cell now -- flowing OUT.

Thus the path of electrons/current in continuous and whatever reactions have to take place within the cell, happens while these electrons are flowing through the cell.

Answer 2

Answer:

Calculate the potential at the centre of a square of side √(4.5)m which carries at its four corners charges of + 5 X10-9 C, +2 X 10-9 C, -5 X 10-9 C and -7 X 10-9 C respectively.