13. A parallel-plate capacitor is charged and then disconnected from the battery. The plate separation is then reduced to half its original value. By what factor does the stored energy in the capacitor change?
(A) It remains the same.
(B) It is doubled.
(C) It decreases by a factor of 2.
(D) It increases by a factor of 4.
(E) It decreases by a factor of 4

14. A charged particle moves through a uniform magnetic field. Which of the following statements about the magnetic force on the particle is true? (A) It exerts a force on the particle parallel to the field. (B) It exerts a force on the particle along the direction of its motion. (C) It increases the kinetic energy of the particle. (D) It changes the momentum of the particle. (E) None of the above.

15. A light ray travels from medium 1 into medium 2, and then into medium 3, as shown in the figure. Which of the following correctly represents the magnitudes of the relative index of refraction, n1, n2, n3? (A) $n3 > n1 > n2$ (B) $n3 > n2 > n1$ (C) $n2 > n3 > n1$ (D) $n1 > n3 > n2$ (E) none of the above. 

16. A plane electromagnetic wave in vacuum propagates in the $+\mathbf{x}$ direction with frequency $f = 900\mathrm{Mhz}$. The magnetic field oscillates perpendicular to $\mathbf{x}$ with amplitude $B_0 = 2.0uT$. What is the expression for electrical field $E(x,t)$? (Use $c = 3\times 10^{8}m / s$). (A) $6.67 \times 10^{-14} \cos(18.85x - 5.65 \times 10^{9}t)$ (B) $600 \cos(18.85x - 5.65 \times 10^{9}t)$ (C) $6.67 \times 10^{-1} \cos(0.33x - 5.65 \times 10^{9}t)$ (D) $600 \cos(0.33x - 5.65 \times 10^{9}t)$

17. A bar magnet is held vertically above a circular conducting loop lying in the horizontal plane, as shown in the figure. The south pole of the magnet faces the loop. The magnet is then released and allowed to fall freely toward the loop. As viewed from above, which statement correctly describes the direction of the induced current in the loop? (A) It is always counterclockwise. (B) It is always clockwise. (C) It is counterclockwise as the magnet falls toward the loop, and then clockwise after it has passed through the loop. (D) It is clockwise as the magnet falls toward the loop, and then counterclockwise after it has passed through the loop. (E) There is no induced current.

18. The RC circuit shown in the figure $(\mathrm{R} = 100\Omega, \mathrm{C} = 10\mu \mathrm{F})$ is called a low-pass filter because it passes low-frequency AC signals with less attenuation than high-frequency signals. The frequency at which the voltage ratio $\mathrm{A} = \mathrm{v_{out}} / \mathrm{v_{in}}$ drops to $1 / \sqrt{2}$ of its maximum value is known as cutoff frequency. What is the cutoff frequency of this circuit?(A) $159.2\mathrm{Hz}$(B) $1\mathrm{kHz}$(C) $6.28\mathrm{kHz}$(D) $1.59\mathrm{MHz}$(E) $10\mathrm{MHz}$

19. A radio-wave transmitter and a receiver are separated by a horizontal distance $d = 60.0 \, \text{m}$. Both antennas are located at a height $h = 40.0 \, \text{m}$ above the ground, as shown in the figure. The receiver detects two signals: one travels directly from the transmitter, and the other is reflected from the ground. Assume the ground is perfectly level and that a $180^{\circ}$ phase shift occurs upon reflection. What is the longest wavelength that results in destructive interference at the receiver?(A) $20.0\mathrm{m}$ (B) $26.7\mathrm{m}$ (C) $40\mathrm{m}$ (D) $80\mathrm{m}$ (E) $160\mathrm{m}$

20. A square coil consists of $N = 10$ closely wrapped turns and has side length $a = 0.50 \, \text{m}$. The coil is hinged along the y-axis, and its plane makes an angle $\theta = 60.0^{\circ}$ with the x-axis, as shown in the figure. The current in the coil is $I = 1.50 \, \text{A}$ in the direction indicated, and the coil is placed in a uniform magnetic field $B = 0.40 \, \text{T}$ directed along the positive x-axis. What is the torque exerted on the coil by the magnetic field, and what is its direction when viewed from above (looking down along the +y-axis)?(A) $0.75\mathrm{N}\cdot \mathrm{m}$ clockwise (B) $0.75\mathrm{N}\cdot \mathrm{m}$ counter-clockwise(C) $1.3\mathrm{N}\cdot \mathrm{m}$ clockwise (D) $1.3\mathrm{N}\cdot \mathrm{m}$ counter-clockwise (E) None of the above

1. 2025年2月份，因水氣充足又夜間低溫，高雄市區形成濃霧及低雲，讓海拔約300多公尺的壽山出現罕見的雲瀑及雲海，屬於「平流霧+輻射霧」，其成因不是下列何者？ (A)暖濕空氣接觸到冷表面 (B)空氣絕熱膨脹冷卻 (C)有充足的凝結核 (D)地表輻 射散熱，降溫至露點。

2. 2026年3月3日19點04分到20點03分發生月全食的天文奇景，若天氣晴朗，臺灣會有哪 一個情形？ (A)臺灣沿海地區這一天會有暴潮 (B)臺灣在此時可看到太陽 (C)月 全食當下，月亮會被地球影子遮住，所以看不到月亮 (D)這一天臺灣各地的潮差比平 常大。

3. 2024年1月1日下午16點10分(日本當地時間)，日本石川縣能登地區發生Mw 7.5的地 震，震源深度為10公里(USGS)，地震主要起源於狼煙沖逆衝斷層，造成大規模劇 烈震動、土壤液化、建築物崩塌、火災等災害，最大震度達7級，最大地表加速度達2.7G。關於這個地震的說明，下列哪個選項是對的？ (A)此地震主要是壓力作用產 生斷層破裂 (B)此地震屬於中源地震 (C)只要地震規模夠大，就一定會發生土壤液 化 (D)此地震發生在歐亞地震帶上。

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