Electric Potential and Potential Difference

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

   คำตอบ: A

   1 Work done by electric force: $W = q ( V A - V B )$. 2 $\mathrm { VA } - \mathrm { VB } = \mathrm { W } / \mathrm { q } = \left( - 8 \times 10 ^ { - 4 } \right) / \left( 4 \times 10 ^ { - 6 } \right) = - 200 \mathrm {~V}$.
   ดูในชุดข้อสอบเต็ม 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
   ดูคำตอบและวิธีทำ

   คำตอบ: 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.
   ทำข้อสอบเต็มชุด CSCA Physics March 2026 Past Paper — จับเวลาและให้คะแนน
3. CSCA Physics April 2026 Past Paper
   A charge of $+ 5 \times 10 ^ { - 6 } \mathrm { C }$ moves from $A$ to $B$. The electric force does $+ 1 \times 10 ^ { - 3 } \mathrm {~J}$ of work. The potential difference $U _ { A B }$ is
   • A．- 200 V
   • B．200 V
   • C．- 0.2 V
   • D．0.2 V
   ดูคำตอบและวิธีทำ

   คำตอบ: B

   $U _ { A B } = \frac { W _ { A B } } { q } = \frac { 1 \times 10 ^ { - 3 } } { 5 \times 10 ^ { - 6 } } = 200 \mathrm {~V}$. (Positive work on a positive charge implies $U _ { A B } > 0$ : the charge moves from higher to lower potential.)
   ทำข้อสอบเต็มชุด CSCA Physics April 2026 Past Paper — จับเวลาและให้คะแนน