UNIT OF WAVELENGTH

Wavelength

Wavelength is defined as the measured distance between two identical points on two consecutive waves. Wavelength can be measured either between two successive crests (topmost points on a wave) or two successive troughs (bottom points on a wave). Starting from the point where the wavelength is measured, the pattern of the wave can be observed to be repeating. Wavelength can be measured in both traveling and standing waves and even in the other spatial wave patterns. Spatial frequency, which is the inverse of frequency, quantifies the number of times the sinusoidal components of a periodic structure repeats per unit of distance in space. Frequency and wavelength are inverse quantities in that when the magnitude of one increases, the value of the other goes down.

Light propagates through free space in the form of transverse waves where the direction of motion of the wave is perpendicular to the direction of oscillation of the photons of the wave. Wavelength is denoted by the Greek letter λ (lambda), and the SI unit is meter (m). However, since wavelength values can tend to be really small, units such as nanometers (nm) or micrometers (µm) are also used. The wavelength, in the case of waves, can be expressed as follows. λ = v/ f Or in the case of particles as E = hf where

• λ is the wavelength of the wave
• v is the speed of the wave. In the case of light waves travelling in a vacuum, the speed is given by the speed of light, denoted by c, which is equal to 3 x 10 8 m/ s.
• f is the frequency with which the photons in the wave oscillate
• E is the energy of the wave
• h is the Planck’s constant (6.64 x 10 -34 joule/ second)

Wavelength in Visible Light

Visible light is made up of multiple waves, each with different wavelength values. Additionally, each value range of the wavelength of visible light corresponds to a different color. Humans perceive the color of an object as a result of the reflection of light waves by that object. For example, when the visible light from the sun falls on the vegetation (trees, grass, shrubs etc.) on Earth, the molecules in them absorb all other wavelengths of light except for that of green. This green light is reflected off the leaves and falls on our eyes, making the leaves look green in color.

The sun, which is the primary source of light for the Earth, produces polychromatic light. That is, the light waves from the sun are considered to be white in color, which is the combination of all the seven visible light spectrum colors. However, in the case of lasers, the light produced will be of one specific color, and is called monochromatic because the color of the light depends on its specific wavelength values. The seven colors of the visible spectrum are violet, indigo, blue, green, yellow, orange and red.

Units of Wavelength

The SI unit of wavelength is meter because the wavelength is a measure of distance. As a measure of speed and distance, one meter is defined as the distance covered by light travelling in a vacuum in a duration of 1/ (3 x 10 8 ) seconds. Since values of wavelength can be extremely small or large in magnitude, multiples of meters are used to express it effectively. Some multiples and submultiples of meters are shown below.

Submultiples:

 Name SI symbol Value Decimeter dm 10-1 m Centimeter cm 10-2 m Millimeter mm 10-3 m Micrometer µm 10-6 m Nanometer nm 10-9 m Picometer pm 10-12 m Femtometer fm 10-15 m Attometer am 10-18 m Zeptometer zm 10-21 m Yoctometer ym 10-24 m

Multiples:

 Name SI symbol Value Decameter dam 101 m Hectometer hm 102 m Kilometer km 103 m Megameter Mm 106 m Gigameter Gm 109 m Tetrameter Tm 1012 m Pentameter Pm 1015 m Exameter Em 1018 m Zettameter Zm 1021 m Yottameter Ym 1024 m

Meter, metric units and other non SI units of distance expressed in terms of each other are given below.

Metric unit expressed in non-SI units:

 1 meter 1.0936 yard 1 meter 39.370 inches 1 centimeter 0.39370 inch 1 millimeter 0.0039370 inch 1 meter 1 x 1010 ångström 1 nanometer 10 ångström

Non-SI unit expressed in metric units:

 1 yard 0.9144 meter 1 inch 0.0254 meter 1 inch 2.54 centimeters 1 inch 25.4 millimeters 1 ångström 1 x 10-10 meter 1 ångström 100 picometers

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