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Next exam on November 14 – 15, 2026:
All concepts

Electric Potential and Potential Difference

电势与电势差

The definition of potential and the choice of zero, how potential relates to field lines, computing potential difference, and the work done by the electrostatic force.

5 real-exam questions · 4 sittings10 in mock papers10 practice

Formulas

  • Work done by the electrostatic force

    Formula
    WAB=qUABW_{AB}=qU_{AB}

    Applies when：Path-independent: it depends only on the potential difference between the endpoints

  • Definition of potential difference

    Definition
    UAB=φA−φB=WABqU_{AB}=\varphi_A-\varphi_B=\frac{W_{AB}}{q}

    Applies when：Potential difference is independent of the zero reference, although potential itself is not

How the real exam tests it

Questions from real CSCA papers that test this concept. Work each one out before you open the answer.

  1. CSCA Physics December 2025 Past Paper
    A point charge with a charge of +4×10−6C+ 4 \times 10 ^ { - 6 } \mathrm { C } is moved from point A to point B in an electric field. The electric force does negative work of 8×10−4 J8 \times 10 ^ { - 4 } \mathrm {~J}. The potential difference between points AA and BB is ( ).
    • A．- 200 V
    • B．200 V
    • C．- 2000 V
    • D．2000 V
    Show answer & solution

    Answer: A

    1 Work done by electric force: W=q(VA−VB)W = q ( V A - V B ). 2 VA−VB=W/q=(−8×10−4)/(4×10−6)=−200 V\mathrm { VA } - \mathrm { VB } = \mathrm { W } / \mathrm { q } = \left( - 8 \times 10 ^ { - 4 } \right) / \left( 4 \times 10 ^ { - 6 } \right) = - 200 \mathrm {~V}.
    See it in the full CSCA Physics December 2025 Past Paper
  2. CSCA Physics March 2026 Past Paper
    In a uniform electric field, which statement is correct?
    • A．Potential is equal everywhere
    • B．Field strength is equal everywhere
    • C．Field lines are curved
    • D．Field direction varies everywhere
    Show answer & solution

    Answer: B

    Uniform field: same magnitude and direction everywhere (B). Lines are parallel and equally spaced (C wrong). Direction is uniform (D wrong). Potential decreases along the field (A wrong). Answer: B.
    Take the full CSCA Physics March 2026 Past Paper — timed & graded
  3. CSCA Physics April 2026 Past Paper
    A charge of +5×10−6C+ 5 \times 10 ^ { - 6 } \mathrm { C } moves from AA to BB. The electric force does +1×10−3 J+ 1 \times 10 ^ { - 3 } \mathrm {~J} of work. The potential difference UABU _ { A B } is
    • A．- 200 V
    • B．200 V
    • C．- 0.2 V
    • D．0.2 V
    Show answer & solution

    Answer: B

    UAB=WABq=1×10−35×10−6=200 VU _ { A B } = \frac { W _ { A B } } { q } = \frac { 1 \times 10 ^ { - 3 } } { 5 \times 10 ^ { - 6 } } = 200 \mathrm {~V}. (Positive work on a positive charge implies UAB>0U _ { A B } > 0 : the charge moves from higher to lower potential.)
    Take the full CSCA Physics April 2026 Past Paper — timed & graded

Real-exam evidence

Recorded past-paper appearances are listed below; online verification is labelled separately.

5 questions across 4 sittings1 of 4 sittings available to verify free online

10 questions across 6 mock papers — our own papers, so a coverage signal rather than real-exam evidence

10 related practice questions availablePractise free: Electrostatics

Sitting evidence comes from the CSCA past papers on record; questions whose original paper is missing are excluded, and sprint papers are deliberately not counted.

Glossary

voltage

Related concepts

Electric Field and Field StrengthSteady Current and DC Circuits