Everything about Amplitude totally explained
Amplitude is the
magnitude of change in the oscillating variable, with each
oscillation, within an oscillating system. For instance,
sound waves are oscillations in
atmospheric pressure and their amplitudes are proportional to the change in
pressure during one oscillation. If a graph of the system is drawn with the oscillating variable as the vertical axis and time as the horizontal axis then the amplitude may be measured as the vertical distance between points on the curve.
Concepts of Amplitude
Peak Amplitude
Peak amplitude is measured between a peak and the rest position of the system. In many sciences this is called
peak amplitude. In
astronomy, when measuring the wobble of a body due to the gravitational influence of another body, it's called the
semi-amplitude[1].
Peak-to-peak Amplitude
Peak-to-peak amplitude is to measure it between peak and trough. Peak-to-peak amplitudes can be measured by
meters with appropriate circuitry, or by viewing the waveform on an
oscilloscope.
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.
Ambiguity of Amplitude
The use of peak amplitude is simple and unambiguous 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 because the value obtained 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 the maximum negative signal (the
peak-to-peak amplitude) and then divided by two.
For complex waveforms, especially non-repeating signals like noise, the RMS amplitude is usually used because it's unambiguous and because it 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).
When dealing with
alternating current electrical power it's universal to specify RMS values of a sinusoidal waveform. It is important to recognise that the peak-to-peak voltage is nearly 3 times the RMS value when assessing safety, specifying components, etc.
Pulse amplitude
In
telecommunication,
pulse amplitude is the magnitude of a
pulse parameter, such as the
field intensity,
voltage level,
current level, or
power level.
Note 1: 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."
Note 2: Pulse amplitude also applies to the amplitude of
frequency- and
phase-modulated
waveform envelopes.
Source: from
Federal Standard 1037C
Amplitude in the Wave Equation
In the simple
wave equation
»
A is the amplitude of the wave.
Units of Amplitude
The units of the amplitude depend on the type of wave.
For waves on a
string, or in medium such as
water, the amplitude is a
displacement.
The amplitude of sound waves and audio signals (also referred to as 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.
Wave Forms and Amplitude
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, but this isn't true for an arbitrary waveform which may or may not be periodic.
For a
sine wave the relationship between RMS and peak-to-peak amplitude is:
» Further Information
Get more info on 'Amplitude'.
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