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The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI) and is defined as one cycle per second.〔"hertz". (1992). ''American Heritage Dictionary of the English Language'' (3rd ed.), Boston: Houghton Mifflin.〕 It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves. One of the unit's most common uses is in the description of sine waves and musical tones, particularly those used in radio and other audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven. == Definition == The hertz is equivalent to cycles per second.〔(【引用サイトリンク】 SI brochure: Table 3. Coherent derived units in the SI with special names and symbols )〕 In defining the second, the International Committee for Weights and Measures declared that "the standard to be employed is the transition between the hyperfine levels F = 4, M = 0 and F = 3, M = 0 of the ground state 2S1/2 of the cesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz" thereby effectively defining the hertz and the second simultaneously. In English, "hertz" is also used as the plural form.〔(NIST Guide to SI Units – 9 Rules and Style Conventions for Spelling Unit Names ), National Institute of Standards and Technology〕 As an SI unit, Hz can be prefixed; commonly used multiples are kHz (kilohertz, 103 Hz), MHz (megahertz, 106 Hz), GHz (gigahertz, 109 Hz) and THz (terahertz, 1012 Hz). One hertz simply means "one cycle per second" (typically that which is being counted is a complete cycle); 100 Hz means "one hundred cycles per second", and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, or a human heart might be said to beat at 1.2 Hz. The rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second (1/s or s−1) in general or, the specific case of radioactive decay, becquerels.〔"(d) The hertz is used only for periodic phenomena, and the becquerel (Bq) is used only for stochastic processes in activity referred to a radionuclide." (【引用サイトリンク】title=BIPM – Table 3 )〕 Whereas 1 Hz is 1 cycle per second, 1 Bq is 1 aperiodic radionuclide event per second. Even though angular velocity, angular frequency and the unit hertz all have the dimension 1/s, angular velocity and angular frequency are not expressed in hertz,〔(【引用サイトリンク】 SI brochure, Section 2.2.2, paragraph 6 )〕 but rather in an appropriate angular unit such as radians per second. Thus a disc rotating at 60 revolutions per minute (rpm) is said to be rotating at either 2 rad/s ''or'' 1 Hz, where the former measures the angular velocity and the latter reflects the number of ''complete'' revolutions per second. The conversion between a frequency ''f'' measured in hertz and an angular velocity ''ω'' measured in radians per second is : and . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hertz」の詳細全文を読む スポンサード リンク
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