U0580. If a conductor is placed in an electrostatic field, the conductor
will exhibit the following characteristics: (Choose all that
apply.)
如果将导体置于静电场中，导体将呈现如下特点：
Exam tips · 考试提示
Statement A is correct physics: at electrostatic equilibrium a
conductor is equipotential, internal field is zero, and excess charge resides on the outer surface. The official answer key
marks A and B. Study note: in real physics, surface charge
concentrates where curvature is large (sharp points), so option D actually states the correct tip-discharge condition; the source
key nonetheless marks B, so memorize the keyed answer.
U0581. Direct current (DC) is defined by the direction of charge
motion never changing. Which of the following descriptions
of direct current is correct? (Choose all that apply.)
直流电（DC）是以电荷的运动方向始终不变来定义的。关于直
流电，以下描述正确的是：
Exam tips · 考试提示
DC has fixed polarity terminals (A) and a battery supplies DC
(B). C is false — 13.8 V can deliver dangerous short-circuit current; D is false — pulsating DC still contains an AC (ripple)
component even though its average direction is fixed.
U0582. Alternating current (AC) is defined by the direction of charge
motion alternating with time. Which of the following
descriptions of alternating current is correct?
交流电（AC）是以电荷的运动方向随时间交替变化来定义的。
关于交流电，以下描述正确的是：
Exam tips · 考试提示
AC polarity alternates, so an AC source has no fixed +/− terminals (A). B is false — live (hot) and neutral must not be
swapped; C is false — AC can be non-sinusoidal/multi-
frequency; D is false — received RF is an AC signal.
U0583. Which of the following terms can be used to describe the
number of times per second that alternating current changes
polarity?
以下哪一个术语可以用来描述交流电每秒改变极性的次数？
Exam tips · 考试提示
The number of polarity reversals per second is the frequency
(频率), measured in hertz (A). Rate (B), wavelength (C), and
pulse rate (D) describe other quantities.
U0584. What is the relationship between the "wavelength" frequently
mentioned by amateur radio operators and the frequency of
radio waves?
业余无线电爱好者经常提及的"波长"与无线电波的频率有什么
关系？
Exam tips · 考试提示
Wavelength λ = c / f (speed of light ÷ frequency); higher
frequency means shorter wavelength (A). B (useless) is false — amateurs use wavelength to name bands (e.g., "20 m"); C and
D invent false fixed ratios.
U0585. The physical quantity "electromotive force (EMF)" describes:
物理量"电动势"描述的是：
Exam tips · 考试提示
电动势 (electromotive force, EMF) is the ability of a source to convert other energy forms into electrical energy (A). B
describes voltage; C describes current; D is not a standard quantity.
U0586. The physical quantity "voltage" describes:
物理量"电压"描述的是：
Exam tips · 考试提示
电压 (voltage) is the electric potential difference that drives
electrons through a circuit (A). B is EMF; C is current; D is not a standard quantity.
U0587. The peak value of a sinusoidal AC voltage or current refers to:
("x＾m" means "x to the power m")
正弦交流电压或电流的峰值（peak value）是指：（"x＾
m"表示"x的m次方"）
Exam tips · 考试提示
峰值 (peak value) is the maximum instantaneous magnitude
measured from zero (A). B confuses peak with RMS (peak × 1/ √2 gives RMS, not the other way); C and D are not definitions.
U0588. The peak-to-peak value of a sinusoidal AC voltage or current
refers to:
正弦交流电压或电流的峰-峰值（peak-to-peak value）是
指：
Exam tips · 考试提示
峰-峰值 (peak-to-peak value) is the total span from the negative
peak to the positive peak (A). B is the peak value; C and D
apply spurious powers/roots.
U0589. The RMS (root-mean-square) voltage of any AC voltage refers
to: ("x＾m" means "x to the power m")
任意交流电压的有效值（RMS voltage）是指：（"x＾m"表
示"x的m次方"）
Exam tips · 考试提示
有效值 (RMS voltage) is the DC voltage that dissipates the same
heat in the same resistor (A) — the heating-equivalent value.
Note: for a pure sine wave, RMS = peak/√2 (which is option D phrased for sine waves only), but the general definition is the
heating equivalence in A, which the key marks.