Question 4
Why is the potential difference a cell supplies to a circuit less than its electromotive force?
The right answer is the one marked above.
A current also flows through the inside of the cell, which has its own resistance. A small potential difference appears across that internal resistance. Subtract it from the e.m.f. and what is left is what reaches the external circuit.
This is why a torch dims as its cells age: the internal resistance rises, so more of the e.m.f. is spent inside the cell and less comes out.