amplitude
American Heritage Dictionary:
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am·pli·tude
(ăm'plĭ-tūd', -tyūd') 
n.
n.
- Greatness of size; magnitude.
- Fullness; copiousness.
- Breadth or range, as of intelligence.
- Astronomy. The angular distance along the horizon from true east or west to the intersection of the vertical circle of a celestial body with the horizon.
- Physics. The maximum absolute value of a periodically varying quantity.
- Mathematics.
- The maximum absolute value of a periodic curve measured along its vertical axis.
- The angle made with the positive horizontal axis by the vector representation of a complex number.
- Electronics. The maximum absolute value reached by a voltage or current waveform.
[Latin amplitūdō, from amplus, large.]
Wiley Book of Astronomy:
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amplitude
(1) The maximum departure of a cyclical quantity from its mean value. (2) The difference between the maximum and minimum magnitudes of a variable star, i.e., the total range of its brightness.
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The maximum magnitude (value without regard to sign) of the disturbance of a wave. The term “disturbance” refers to that property of a wave which perturbs or alters its surroundings. It may mean, for example, the displacement of mechanical waves, the pressure variations of a sound wave, or the electric or magnetic field of light waves. Sometimes in older texts the word amplitude is used for the disturbance itself; in that case, amplitude as meant there is called peak amplitude. This is no longer common usage.
If the medium which a wave disturbs dissipates the wave by some nonlinear behavior or other means, then the amplitude will, in general, depend upon position. See also Light; Sound; Wave motion.
Computer Desktop Encyclopedia:
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amplitude
The strength or volume of a signal, usually measured in decibels. See wavelength.
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Roget's Thesaurus:
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amplitude
noun
- Great extent, amount, or dimension: bulk, magnitude, mass, size, volume (often used in plural). See big/small/amount.
- The quality or state of being large in amount, extent, or importance: bigness, greatness, largeness, magnitude, sizableness, size. See big/small/amount.
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Of oscillation or vibration, the maximum displacement from the mean position.
Columbia Encyclopedia:
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amplitude
amplitude (ăm'plĭtūd'), in physics, maximum displacement from a zero value or rest position. In the harmonic motion of a pendulum, the amplitude of the swing is the greatest distance reached to either side of the central rest position. Amplitude is important in the description of a wave phenomenon such as light or sound. In general, the greater the amplitude of the wave, the more energy it transmits (e.g., a brighter light or a louder sound).
Investopedia Financial Dictionary:
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Amplitude
The difference in price from the midpoint of a trough to the midpoint of a peak of a security. Amplitude is positive when calculating a bullish retracement (when calculating from trough to peak) and negative when calculating a bearish retracement (when calculating from peak to trough).
Investopedia Says:
Amplitude is calculated often in technical analysis. For example, it is the amount of retracement in a price and also the width of a channel in a range-bound market.
Chart pattern analysis says that after a retracement, price will continue to move at least a distance equal to the retracement's amplitude.
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Hate getting stopped out right before the price reverses? This forex trading strategy may help. Forex: The Memory Of Price Strategy
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McGraw-Hill Dictionary of Aviation:
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amplitude
i. The amplitude of a wave is the maximum displacement, or the maximum value, it attains from its mean position during a cycle. It is both positive and negative. With sound waves, the greater the amplitude, the louder is the sound.
ii. Angular distance north or south of the prime vertical; the arc of the horizon or the angle at the zenith between the prime vertical and a vertical circle, measured north or south from the prime vertical circle. The term is used customarily only to refer to bodies whose centers are on the celestial horizon and is prefixed “E” or “W” as the body is rising or setting, respectively, and suffixed “N” or “S” to agree with the declination.
ii. Angular distance north or south of the prime vertical; the arc of the horizon or the angle at the zenith between the prime vertical and a vertical circle, measured north or south from the prime vertical circle. The term is used customarily only to refer to bodies whose centers are on the celestial horizon and is prefixed “E” or “W” as the body is rising or setting, respectively, and suffixed “N” or “S” to agree with the declination.
Oxford Dictionary of Biochemistry:
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amplitude
Saunders Veterinary Dictionary:
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amplitude
Largeness, fullness; wideness or breadth of range or extent.
- a. mode — see A-mode ultrasonography.
Random House Word Menu:
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categories related to 'amplitude'
- Electricity and Electronics - amplitude: maximum deviation of AC current from its average value during its cycle; peak value of waveform
Wikipedia on Answers.com:
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Amplitude
For quantum-mechanical amplitude, see probability amplitude. For the video game of the same name, see Amplitude (video game). Peak to Peak redirects here. For the school of that name, see Peak to Peak Charter School
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This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2007) |
Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system is drawn with the oscillating variable as the vertical axis and time as the horizontal axis, the amplitude is visually represented by the vertical distance between the extrema of the curve and the equilibrium value.
In older texts the phase is sometimes very confusingly called the amplitude.[1]
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Contents
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Concepts
Peak-to-peak amplitude
Peak-to-peak amplitude is the change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative). With appropriate circuitry, peak-to-peak amplitudes can be measured by meters or by viewing the waveform on an oscilloscope. Peak-to-peak is a straightforward measurement on an oscilloscope, the peaks of the waveform being easily identified and measured against the graticule. This remains a common way of specifying amplitude, but sometimes other measures of amplitude are more appropriate.
Peak amplitude
In audio system measurements, telecommunications and other areas where the measurand is a signal that swings above and below a zero value but is not sinusoidal, peak amplitude is often used. This is the maximum absolute value of the signal.
Semi-amplitude
Semi-amplitude means half the peak-to-peak amplitude.[2] It is the most widely used measure of orbital amplitude in astronomy and the measurement of small semi-amplitudes of nearby stars is important in the search for exoplanets.[3] For a sine wave, peak amplitude and semi-amplitude are the same.
Some scientists[4] use "amplitude" or "peak amplitude" to mean semi-amplitude, that is, half the peak-to-peak amplitude.[2]
Root mean square amplitude
Root mean square (RMS) amplitude is used especially in electrical engineering: the RMS is defined as the square root of the mean over time of the square of the vertical distance of the graph from the rest state.[5]
For complex waveforms, especially non-repeating signals like noise, the RMS amplitude is usually used because it is both unambiguous and has physical significance. For example, the average power transmitted by an acoustic or electromagnetic wave or by an electrical signal is proportional to the square of the RMS amplitude (and not, in general, to the square of the peak amplitude).[6]
1 = Peak amplitude (
),2 = Peak-to-peak amplitude (
),3 = RMS amplitude (
),4 = Wave period (not an amplitude)
For alternating current electrical power, the universal practice is to specify RMS values of a sinusoidal waveform. One property of root mean square voltages and currents is that they produce the same heating effect as DC in a given resistance.
The peak-to-peak voltage of a sine wave is about 2.8 times the RMS value. The peak-to-peak value is used, for example, when choosing rectifiers for power supplies, or when estimating the maximum voltage insulation must withstand. Some common voltmeters are calibrated for RMS amplitude, but respond to the average value of a rectified waveform. Many digital voltmeters and all moving coil meters are in this category. The RMS calibration is only correct for a sine wave input since the ratio between peak, average and RMS values is dependent on waveform. If the wave shape being measured is greatly different from a sine wave, the relationship between RMS and average value changes. True RMS-responding meters were used in radio frequency measurements, where instruments measured the heating effect in a resistor to measure current. The advent of microprocessor controlled meters capable of calculating RMS by sampling the waveform has made true RMS measurement commonplace.
Ambiguity
In general, the use of peak amplitude is simple and unambiguous only for symmetric periodic waves, like a sine wave, a square wave, or a triangular wave. For an asymmetric wave (periodic pulses in one direction, for example), the peak amplitude becomes ambiguous. This is because the value is different depending on whether the maximum positive signal is measured relative to the mean, the maximum negative signal is measured relative to the mean, or the maximum positive signal is measured relative to the maximum negative signal (the peak-to-peak amplitude) and then divided by two. In electrical engineering, the usual solution to this ambiguity is to measure the amplitude from a defined reference potential (such as ground or 0 V). Strictly speaking, this is no longer amplitude since there is the possibility that a constant (DC component) is included in the measurement.
Pulse amplitude
In telecommunication, pulse amplitude is the magnitude of a pulse parameter, such as the voltage level, current level, field intensity, or power level.
Pulse amplitude is measured with respect to a specified reference and therefore should be modified by qualifiers, such as "average", "instantaneous", "peak", or "root-mean-square".
Pulse amplitude also applies to the amplitude of frequency- and phase-modulated waveform envelopes.[7]
Formal representation
In this simple wave equation
A is the peak amplitude of the wave,
x is the oscillating variable,
t is time,
K and b are arbitrary constants representing time and displacement offsets respectively.
The units of the amplitude depend on the type of wave, but are always in the same units as the oscillating variable. A more general representation of the wave equation is more complex, but the role of amplitude remains analogous to this simple case.
For waves on a string, or in medium such as water, the amplitude is a displacement.
The amplitude of sound waves and audio signals (which relates to the volume) conventionally refers to the amplitude of the air pressure in the wave, but sometimes the amplitude of the displacement (movements of the air or the diaphragm of a speaker) is described. The logarithm of the amplitude squared is usually quoted in dB, so a null amplitude corresponds to −∞ dB. Loudness is related to amplitude and intensity and is one of most salient qualities of a sound, although in general sounds can be recognized independently of amplitude. The square of the amplitude is proportional to the intensity of the wave.
For electromagnetic radiation, the amplitude of a photon corresponds to the changes in the electric field of the wave. However radio signals may be carried by electromagnetic radiation; the intensity of the radiation (amplitude modulation) or the frequency of the radiation (frequency modulation) is oscillated and then the individual oscillations are varied (modulated) to produce the signal.
Waveform and envelope
The amplitude may be constant (in which case the wave is a continuous wave) or may vary with time and/or position. The form of the variation of amplitude is called the envelope of the wave.
If the waveform is a pure sine wave, the relationships between peak-to-peak, peak, mean, and RMS amplitudes are fixed and known, as they are for any continuous periodic wave. However, this is not true for an arbitrary waveform which may or may not be periodic or continuous.
For a sine wave the relationship between RMS and peak-to-peak amplitude is:
.
For other waveforms the relationships are not (necessarily) arithmetically the same as they are for sine waves.
See also
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Look up amplitude in Wiktionary, the free dictionary. |
- Waves and their properties:
- Amplitude modulation
Notes
- ^ Knopp, Konrad; Bagemihl, Frederick (1996). Theory of Functions Parts I and II. Dover Publications. p. 3. ISBN 0-486-69219-1.
- ^ a b Tatum, J. B. Physics - Celestial Mechanics. Paragraph 18.2.12. 2007. Retrieved 2008-08-22.
- ^ Uriel A. Goldvais. Exoplanets, pp.2-3.
- ^ Regents of the University of California. Universe of Light: What is the Amplitude of a Wave? 1996. Retrieved 2008-08-22
- ^ Department of Communicative Disorders University of Wisconsin–Madison. RMS Amplitude. Retrieved 2008-08-22
- ^ Ward, Electrical Engineering Science, pp141-142, McGraw-Hill, 1971.
- ^
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Amplitude
Dansk (Danish)
n. - vidde, udstrækning
Nederlands (Dutch)
amplitude, uitgestrektheid, overvloed
Français (French)
n. - (Astron, Phys) amplitude, ampleur (d'une pensée)
Deutsch (German)
n. - (electr.) Amplitude, Schwingungsweite
Ελληνική (Greek)
n. - εύρος, πλάτος, ευρύτητα, αφθονία
Italiano (Italian)
ampiezza, abbondanza
Português (Portuguese)
n. - amplitude (f), extensão (f), abundância (f), plenitude (f)
Español (Spanish)
n. - amplitud, extensión, abundancia
Svenska (Swedish)
n. - vidd, bredd, amplitud
中文（简体）(Chinese (Simplified))
广阔, 广大, 振幅, 丰富, 充足, 射程
中文（繁體）(Chinese (Traditional))
n. - 廣闊, 廣大, 振幅, 豐富, 充足, 射程
日本語 (Japanese)
n. - 広さ, 豊富, 振幅
العربيه (Arabic)
(الاسم) اتساع, وفره, مدى, نطاق
עברית (Hebrew)
n. - גודל, משרעת, שפע, שפעה
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