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.
U0590. The physical quantity "current" describes:
物理量"电流"描述的是：
Exam tips · 考试提示
电流 (current) is charge flow per unit time — here described as electrons passing per unit time (A). B is not a standard
quantity; C lacks the "per unit time" rate; D is drift speed, not
current.
U0591. The physical quantity "resistance" describes:
物理量"电阻"描述的是：
Exam tips · 考试提示
电阻 (resistance) is a circuit's opposition to current flow
between two points (A). B and C describe energy (that is power dissipation, not resistance itself); D describes a time, which
resistance is not.
U0592. The physical quantity "power" describes:
物理量"功率"描述的是：
Exam tips · 考试提示
功率 (power) is work (energy) per unit time — here, the work done by current per unit time (A). B and C are energy (not
rate); D is not a quantity of power.
U0593. Ohm's law for DC circuits states: (Choose all that apply.)
直流电路欧姆定律是说：
Exam tips · 考试提示
Ohm's law: I = U/R, so current is proportional to voltage and
inversely proportional to resistance (A); equivalently U = I·R, so voltage is proportional to both current and resistance (B). C
wrongly makes current proportional to R; D wrongly makes voltage inversely proportional to R.
U0594. The kinds of current that are not impeded by resistance in a
circuit are:
在电路中不受电阻阻碍的电流，种类如下：
Exam tips · 考试提示
Every real current encounters resistance (including RF, audio,
and DC), so there is no kind of current free of resistive opposition (A). B/C/D all do experience resistance.
U0595. The term "impedance" describes:
术语"阻抗"描述的是：
Exam tips · 考试提示
阻抗 (impedance) is the general AC opposition a circuit
presents between two points — combining resistance and reactance (A). B describes a capacitor-like behavior, C an
inductor-like behavior, D a filter behavior; none is the general definition.