Question

Explain why the potential difference between the terminals of the cell is more in open circuits and less in closed circuits?

Answer 1

There is some internal resistance for every cell. Now if current flows there will be some potential drop across the internal resistance. So the potential difference will be little less than the total electromotive force (EMF) of the cell.

Now since in open circuit there is no current, there is no potential drop across the internal resistance so the measured potential difference is equal to the total EMF of the cell.

In closed circuit there will be a current flow and hence the potential difference will be less than total EMF of cell and hence less than the open circuit.