Wavelength, Amplitude, and Frequency

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WAVELENGTH

Wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests, or troughs, or corresponding zero crossingsas shown.

In physics, the Wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.^[1] It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns.^[2][3] Wavelength is commonly designated by the Greek letter lambda (λ). The concept can also be applied to periodic waves of non-sinusoidal shape.^[1][4] The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.^[5] The SI unit of wavelength is the meter.

Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths.^[6]

Examples of wave-like phenomena are sound waves, light, and water waves. A sound wave is a periodic variation in air pressure, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary. Water waves are periodic variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary periodically in both lattice position and time.

Wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle in the water moves in a circle of the same diameter as the wave height, unrelated to wavelength.^[7]

Contents  [hide] 1 Sinusoidal waves 1.1 Standing waves 1.2 Mathematical representation 1.3 General media 1.3.1 Nonuniform media 1.3.2 Crystals 2 More general waveforms 2.1 Envelope waves 2.2 Wave packets 3 Interference and diffraction 3.1 Double-slit interference 3.2 Single-slit diffraction 3.3 Diffraction-limited resolution 4 Subwavelength 5 See also 6 References 7 External links

AMPLITUDE

A sinusoidal curve
1 = Peak amplitude (),
2 = Peak-to-peak amplitude (),
3 = RMS amplitude (),
4 = Wave period (not an amplitude)

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]

Contents  [hide] 1 Concepts 1.1 Peak-to-peak amplitude 1.2 Peak amplitude 1.3 Semi-amplitude 1.4 Root mean square amplitude 1.5 Ambiguity 1.6 Pulse amplitude 2 Formal representation 3 Waveform and envelope 4 See also 5 Notes

FREQUENCY

Three cyclically flashing lights, from lowest frequency (top) to highest frequency (bottom). f is the frequency in hertz (Hz), meaning the number of cycles per second. T is the period in seconds (s), meaning the number of seconds per cycle. T and f arereciprocals.

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period (the interval between beats) is half a second.

Contents  [hide] 1 Definitions and units 2 Measurement 2.1 By counting 2.2 By stroboscope 2.3 By frequency counter 2.4 Heterodyne methods 3 Frequency of waves 4 Examples 4.1 Physics of light 4.2 Physics of sound 4.3 Line current 5 Period versus frequency 6 Other types of frequency 7 Frequency ranges 8 See also 9 References 10 Further reading 11 External links