CRAC Class B (2025) — Questions 891–900
U0606. In the system of legal units of measurement, what are the mathematical significance and textual meaning of the prefix μ? ('x＾m' denotes 'x to the power of m'.)
在法定计量单位中，词头μ的数学意义和文字含义分别为： （“x＾m”表示“x的m次方”）
Exam tips · 考试提示
The prefix μ (micro, 微) represents 10^-6. Option A is correct. B is mega, C is milli, and D is kilo — all different prefixes.
U0607. In the system of legal units of measurement, what are the mathematical significance and textual meaning of the prefix G? ('x＾m' denotes 'x to the power of m'.)
在法定计量单位中，词头G的数学意义和文字含义分别为： （“x＾m”表示“x的m次方”）
Exam tips · 考试提示
The prefix G (giga, 吉) represents 10^9. Option A is correct. B (mega, 10^6), C (tera, 10^12), and D (pico, 10^-12) are different prefixes.
U0608. In the system of legal units of measurement, what are the mathematical significance and textual meaning of the prefix n? ('x＾m' denotes 'x to the power of m'.)
在法定计量单位中，词头n的数学意义和文字含义分别为： （“x＾m”表示“x的m次方”）
Exam tips · 考试提示
The prefix n (nano, 纳) represents 10^-9. Option A is correct. B is giga, C is tera, and D is pico — all different prefixes.
U0609. In the system of legal units of measurement, what are the mathematical significance and textual meaning of the prefix T? ('x＾m' denotes 'x to the power of m'.)
在法定计量单位中，词头T的数学意义和文字含义分别为： （“x＾m”表示“x的m次方”）
Exam tips · 考试提示
The prefix T (tera, 太) represents 10^12. Option A is correct. B (pico, 10^-12), C (giga, 10^9), and D (nano, 10^-9) are all different prefixes.
U0610. In the system of legal units of measurement, what are the mathematical significance and textual meaning of the prefix p? ('x＾m' denotes 'x to the power of m'.)
在法定计量单位中，词头p的数学意义和文字含义分别为： （“x＾m”表示“x的m次方”）
Exam tips · 考试提示
The prefix p (pico, 皮) represents 10^-12. Option A is correct. B (tera, 10^12), C (nano, 10^-9), and D (giga, 10^9) are different prefixes.
U0611. Which of the following amateur radio abbreviations can express the term "radio frequency" or specifically refer to a certain frequency used for radio purposes?
以下哪个业余无线电通信缩语可以表述术语“射频”或特指无 线电用途的某个频率？
Exam tips · 考试提示
RF (radio frequency, 射频) is the abbreviation that denotes radio frequency or a radio-used frequency. HF (high frequency), AF (audio frequency), and MF (medium frequency) are band/signal designations, not the general term for radio frequency itself.
U0612. The term "audio frequency" (音频) refers to the frequency of sounds that people can generally hear. Which of the following descriptions is correct?
术语“音频”是指人们可以普遍听到的声音的频率。以下描述 正确的是：
Exam tips · 考试提示
音频 (audio frequency) is the range of sound audible to humans, approximately 16 Hz to 20 kHz (A). C gives a too-high and too-narrow range, and B/D wrongly place audio inside radio bands (VLF–MF, VHF) — audio is a baseband signal, not a radio-frequency band.
U0613. The commonly used nominal impedances of the transmission interfaces for radio communication and related test equipment, television equipment, and audio equipment are, respectively:
无线电通信及相关测试设备、电视设备和音频设备常用的传输 接口标称阻抗分别为：
Exam tips · 考试提示
Radio/RF and test equipment commonly use a 50 ohm interface, television (coaxial) equipment uses 75 ohm, and audio (balanced line) equipment uses 600 ohm. Option A lists them in the correct order: 50 Ω, 75 Ω, 600 Ω.
U0614. 1,805,000 Hz can be expressed as:
1,805,000Hz可以表述为：
Exam tips · 考试提示
1,805,000 Hz = 1.805 × 10^6 Hz = 1.805 MHz. Option A is correct. B (kHz) would be 1,000 times too small, C (mHz = 10^-3 Hz) is absurd, and D (GHz) is 1,000 times too large.
U0615. 2430 MHz can be expressed as:
2430MHz可以表示为：
Exam tips · 考试提示
2430 MHz = 2.430 × 10^9 Hz = 2.43 GHz. Option A is correct. B (243 GHz) is 100× too large, C (nHz) is vanishingly small, and D (kHz) is 10^6× too small.