Wavelength
Wavelength refers to the distance between consecutive crests or troughs of a wave, which is a fundamental characteristic of both sound and electromagnetic (EM) waves. Waves are cyclic disturbances that can be described by parameters such as frequency, which indicates how often the wave cycles occur within a specific time frame, and velocity, the speed at which the wave travels through a medium. The electromagnetic spectrum encompasses a continuous range of wavelengths, from radio waves to gamma rays, with visible light representing a small segment of this spectrum.
In the context of sound waves, their behavior is often described as longitudinal waves, where particle displacement occurs in the same or opposite direction of the wave. Conversely, EM waves are transverse waves, with their electric and magnetic components oscillating at right angles to the direction of propagation. Each category of wave has specific applications influenced by its wavelength; for example, lower frequency waves are commonly used in communication technologies, while higher frequency waves like x-rays and gamma rays have unique properties that allow them to penetrate solid materials and interact with atomic structures.
Overall, understanding wavelength is crucial in various scientific and technological fields, as it plays a significant role in how waves interact with matter, the resolution of imaging devices, and the transmission of information across different mediums.
Wavelength
FIELDS OF STUDY: Electromagnetism; Electronics
ABSTRACT: This article discusses aspects of physical and electromagnetic waves, with regard to their wavelength. Waves are described as either longitudinal or transverse. The time required for one cycle of any wave is the period of the wavelength. Wavelengths are related to both the frequency and the speed at which waves travel through a medium.
Principal Terms
- aperture: an adjustable opening in a barrier through which light or other electromagnetic emission can pass.
- crest: the highest point of a wave from its neutral value.
- electromagnetic spectrum: the continuous range, or continuum, of the frequencies of electromagnetic waves.
- frequency: the number of cycles of a property that occur in a certain amount of time.
- resolution: the ability of a detector to differentiate or separate different wavelengths.
- phase: a stage in a wave property; typically used to describe the relationship of two or more waves.
- trough: the lowest point of a wave from its neutral value.
- velocity: the speed and direction of motion.
Wave Characteristics
All waves can be thought of as cyclic disturbances in some property. The number of times that the cycle occurs in a certain amount of time is the frequency of the wave. When there is no disturbance, a property (such as a wave) has a neutral value. For waves, the value of the property alternates continuously between equal positive and negative variations. The crest (high point) and trough (low point) seen in water waves are classic examples. The neutral value of a water wave is a perfectly smooth surface. As a water wave progresses, the level rises to a maximum value at the crest, then falls to an equal distance below the neutral point in the trough. Such a "sinusoidal" wave (one that is shaped like a sine curve) is at its neutral value three times in each cycle: at the beginning, the middle, and the end. Wavelength is the distance between adjacent crests or troughs.
Sound waves behave in a similar manner. Sound waves and water waves are examples of "longitudinal" waves. Their particles displace in either the same or the opposite direction (depending on the type) of the wave. A medium’s effect on a wave can be seen in the compression-rarefaction sequence. Compression displaces matter from its neutral value. Rarefaction displaces the matter in the opposite sense. Graphs of displacement in both sound waves and water waves exhibit sinusoidal shapes.
The velocity of longitudinal waves depends on the density of the medium through which they travel. The denser the medium, the faster longitudinal waves travel through. The speed of sound in air, for example, is 331 meters per second (1,087 feet per second) at 0 degrees Celsius (32 degrees Fahrenheit) and 342 meters per second (1,123 feet per second) at 18 degrees Celsius (65 degrees Fahrenheit). In water, the speed of sound is about 1,140 meters per second (4,724 feet per second). The density of liquid water is about 770 times that of air.
The waves of the electromagnetic spectrum are described as "transverse" waves because the direction of their displacement is at right angles to the direction of their spread. Electromagnetic (EM) waves are not as simply described as longitudinal or physical waves because they are independent of matter and do not spread in the same way. An EM wave is perhaps best thought of as the vector combination of an electric value and a magnetic value with a single velocity. All EM waves travel at the speed of light. The magnitudes of the electric and magnetic components of an EM wave exhibit are sinusoidal, as is typical of other kinds of waves and wavelike cyclic behaviors.
The Electromagnetic Spectrum
The EM spectrum is a continuum of wavelengths, or frequencies, ranging from zero to infinity. The complete absence of any EM wave is the zero point, having neither frequency nor wavelength. At the opposite extreme, frequencies and wavelengths are theorized to become so compacted as to be indistinguishable from solid matter. Visible light, detectable by the human eye, makes up just one small part of the EM spectrum, with wavelengths ranging from 770 nanometers to 400 nanometers. (A nanometer is one-billionth of a meter.) The corresponding frequencies range from about 1013 to 1016 hertz (Hz). (One hertz is one cycle per second.) By comparison, x-rays have frequencies of about 1018 Hz, and gamma rays have frequencies of 1020 Hz and beyond.
The frequency (f) and the wavelength (λ) of EM radiation are inversely related. The greater the frequency is, the shorter the wavelength. The common factor for all EM radiation is its velocity (v), the speed of light. Unlike longitudinal waves, the velocity of EM waves is constant rather than dependent on the medium. As a result, considering the speed of EM waves is generally not useful in practical applications. Instead, an EM wave is referred to by its frequency in hertz or its wavelength in meters. In spectroscopy, the designation of "wave number" is commonly used. The wave number of an EM frequency is the reciprocal of the wavelength, normally stated in 1/cm.
Applications
EM radiation has a number of applications determined by the wavelength range of the appropriate frequencies. Analytical applications rely on the interaction between the particular EM radiation and the electron cloud in atoms and molecules. Lower frequencies have longer wavelengths and can be used in communications. Adjusting amplitude and phase relations of EM signals enables the speed-of-light transmission of information by radio waves and microwaves. The wavelengths of this region of the EM spectrum are mostly too large to interact effectively with atoms and molecules. Such interaction cannot happen until the energy and wavelengths of the EM waves become similar in dimension to those of the atoms and molecules. Thus, microwaves effectively transmit energy into materials placed in a microwave oven by stimulating the vibrational energy of water molecules and certain kinds of chemical bonds in the material.
Wavelength continues to decrease into and across the infrared and visible region of the EM spectrum. All wavelengths of EM radiation from this point on have application in analytical methods because they can interact with matter in specific ways. Infrared, visible, and ultraviolet wavelengths are readily absorbed and emitted by atoms and molecules. Electrons’ patterns of absorbing or emitting EM wavelengths are routinely analyzed and used for identification and monitoring methods. Above the ultraviolet range of wavelengths are the x-ray wavelengths. These wavelengths are too short to interact with electrons effectively. However, they are closer in size to atomic nuclei and can interact with the nuclear structure of atoms. Thus, they are able to pass through solid matter fairly readily and can be diffracted by the nuclei of atoms. X-ray diffraction is used to analyze crystal structures and solid surfaces. Above the x-ray range of wavelengths are the gamma-ray wavelengths. Because of their extremely high energy and short wavelength, gamma rays destroy matter, and their use is very limited outside of astronomy.
Wavelength and Resolution
The wavelengths of EM radiation are typically detected by electronic devices that convert the analog frequency of the radiation into a digital equivalent. Such detectors use an aperture to restrict the EM radiation that enters the device, where it is then resolved into component wavelengths. The resolution of the devices depends strictly on the ability of gratings and other components to differentiate the wavelengths of the light or other EM radiation that they receive. The finer the resolution, the more precise the incoming information is. High-definition cameras, microscopes, and telescopes, for example, provide clearer images than devices with lower resolution.
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