Voltage as potential difference and work per unit charge

Steps:

• Voltmeter reads 1V, indicating potential at P is 1V higher than at Q.
• Potential difference V equals work done W per unit positive charge q moved from lower to higher potential: V = W/q.
• For +1C charge, q = +1C, so W = V × q = 1V × 1C = 1J.
• Direction from Q (lower potential) to P (higher potential) requires 1J input energy.

Why B is correct:

• Definition of electric potential difference: V = W/q for positive charge moved from lower to higher potential point.

Why the others are wrong:

• A: Moving +1C from P (higher) to Q (lower) releases 1J, so energy needed is -1J (or 0 input).
• C: Electron has charge -1.6×10^{-19}C; energy for one from P to Q is tiny (-1.6×10^{-19}J), not 1J.
• D: For electron from Q to P, direction aligns with field for negative charge, releasing energy, not requiring 1J.

Final answer: B