Answer the following with reference to electric potential difference.
(a) Define electric potential difference between two points in an electric field.
(b) State the sign convention for the work done when a charge is moved (i) along the direction of the electric field and (ii) against the direction of the electric field.
(c) Write the mathematical relation connecting work done, charge moved and potential difference, clearly mentioning the meaning of each symbol.
(d) If moving a unit positive charge from point R to point S requires positive work by an external agent, which point is at a higher potential? Justify your answer briefly.