Name: measuring light with wavelength and frequency
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 12 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

The Wave Nature of Light

La lumière du soleil, les micro-ondes utilisées pour cuisiner et les ondes radio émises par les routeurs wi-fi sont tous des exemples de rayonnement électromagnétique. Le rayonnement électromagnétique est la transmission de l'énergie qui provient du mouvement des particules chargées électriquement. Ce mouvement crée des champs électriques et magnétiques oscillants perpendiculaires se propageant dans l'espace sous la forme d'ondes.Comme toutes les ondes, les ondes électromagnétiques sont caractérisées par leur amplitude, longueur d'onde et la fréquence. L'amplitude de crête est la distance entre la ligne médiane et le pic ou creux d'une onde. Il détermine l'intensité de l'onde.Par exemple, l'amplitude de la lumière visible est liée à sa luminosité;plus l'amplitude est grande, plus la lumière est brillante ou intense. La longueur d'onde est la distance entre des points identiques sur des ondes adjacentes, telles que des pics ou des creux successifs;elle est symbolisée par la lettre grecque lambda. Le rayonnement électromagnétique peut être classé par longueur d'onde, qui peut aller de kilomètres à picomètres.Par exemple, la gamme de longueurs d'onde de la lumière visible est d'environ 400 à 750 nanomètres, ce qui correspond à la lumière violette et rouge, respectivement. La fréquence, qui est symbolisée par la lettre grecque nu, est le nombre de cycles d'ondes qui passent à travers un point de référence en une seconde et est mesurée en hertz, ou cycles par seconde. La longueur d'onde est la largeur d'un cycle.La vitesse d'une onde est le produit de la fréquence et de longueur d'onde. Par conséquent, la fréquence d'une onde est directement proportionnelle à la vitesse à laquelle l'onde se déplace. Cependant, il est inversement proportionnelle à sa longueur d'onde.Par conséquent, les ondes de grande longueur d'onde, telles que les ondes radio, ont des fréquences basses. Ces ondes sont moins énergétiques que les ondes avec des fréquences élevées et des longueurs d'onde courtes, telles que les rayons gamma.

le caractère ondulatoire de la lumière

La nature de la lumière a fait l'objet d'une enquête depuis l'antiquité. Au XVIIe siècle, Isaac Newton a réalisé des expériences avec des lentilles et des prismes, et il a pu démontrer que la lumière blanche se compose des couleurs individuelles de l'arc-en-ciel combinées ensemble. Newton a expliqué ses résultats optiques du point de vue " corpusculaire " de la lumière, dans lequel la lumière était composée de flux de particules extrêmement petites se déplaçant à des vitesses élevées selon les lois du mouvement de Newton.  
 
 D'autres au XVIIe siècle, comme Christiaan Huygens, avaient montré que des phénomènes optiques, tels que la réflexion et la réfraction, pouvaient également être expliqués en termes de lumière telle des ondes se propageant à grande vitesse à travers un milieu appelé " éther luminifère " qui était censé imprégner tout l'espace. Au début du XIXe siècle, Thomas Young a démontré que la lumière passant par des fentes étroites et étroitement espacées produisait des modèles d'interférence qui ne pouvaient pas être expliqués en termes de particules newtoniennes, mais qui pouvaient être facilement expliqués en termes d'ondes. Plus tard au XIXe siècle, après que James Clerk Maxwell ait développé sa théorie du rayonnement électromagnétique et montré que la lumière était la partie visible d'un vaste spectre d'ondes électromagnétiques, la vision de particule de la lumière a été complètement discréditée.  
 
 À la fin du XIXe siècle, les scientifiques considéraient l'univers physique comme comportant à peu près deux domaines distincts : la matière composée de particules se déplaçant selon les lois du mouvement de Newton et le rayonnement électromagnétique composé d'ondes régies par les équations de Maxwell. Aujourd'hui, ces domaines sont appelés mécanique classique et électrodynamique classique (ou électromagnétisme classique). Bien qu'il y avait quelques phénomènes physiques qui ne pouvaient être expliqués dans ce cadre, les scientifiques de l'époque étaient si confiants de la solidité globale de ce cadre qu'ils considéraient ces aberrations comme des paradoxes déroutants qui seraient finalement résolus, d'une manière ou d'une autre, dans ce cadre. Ces paradoxes ont conduit à un cadre contemporain qui relie intimement les particules et les ondes à un niveau fondamental appelé la dualité onde-particule, qui a remplacé la vision classique. 
 
 La lumière visible et les autres formes de rayonnement électromagnétique jouent un rôle important en chimie puisqu'elles peuvent être utilisées pour déduire les énergies des électrons à l'intérieur des atomes et des molécules. Une grande partie de la technologie moderne est basée sur le rayonnement électromagnétique. Par exemple, les ondes radio provenant d'un téléphone portable, les rayons X utilisés par les dentistes, l'énergie utilisée pour cuire des aliments dans votre four micro-ondes, la chaleur rayonnante provenant d'objets chauds rouges et la lumière de votre écran de télévision sont des formes de rayonnement électromagnétique qui présentent toutes un comportement ondulatoire. 
 
 <h4>Ondes </h4>
 
 Une onde est une oscillation, ou un mouvement périodique, qui peut transporter de l'énergie d'un point de l'espace à un autre. Des exemples courants d'ondes se trouvent tout autour de nous. Secouer l'extrémité d'une corde transfère l'énergie de votre main à l'autre extrémité de la corde, faire tomber un galet dans un étang provoque des vagues se propageant vers l'extérieur le long de la surface de l'eau, et la dilatation de l'air qui accompagne un coup de foudre génère des ondes sonores (tonnerre) qui peuvent se déplacer vers l'extérieur sur plusieurs kilomètres. Dans chacun de ces cas, l'énergie cinétique est transférée par la matière (la corde, l'eau ou l'air) alors que la matière reste essentiellement en place.  
 
 Les ondes ne doivent pas être restreintes pour se propager à travers la matière. Comme Maxwell l'a montré, les ondes électromagnétiques consistent en un champ électrique oscillant par pas avec un champ magnétique perpendiculaire, tous deux étant perpendiculaires à la direction de la propagation. Ces ondes peuvent se propager dans le vide à une vitesse constante de 2,998 &times 108 m/s, la vitesse de la lumière (notée c). 
 
 Toutes les ondes, y compris les formes de rayonnement électromagnétique, sont caractérisées par une longueur d'onde (notée λ, la lettre grecque lambda en minuscule), par une fréquence (notée ν, la lettre grecque nu en minuscule) et par une amplitude.  
 
 La longueur d'onde est la distance entre deux pics ou creux consécutifs dans une onde (mesurée en mètres dans le système SI). Les ondes électromagnétiques ont des longueurs d'onde qui se situent sur une plage énorme ; des longueurs d'onde allant des kilomètres (103 m) aux picomètres (10−12 m) ont été observées. La fréquence est le nombre de cycles d'une onde qui passent par un point précis dans l'espace pendant une durée de temps précise (dans le système si, ceci est mesuré en secondes). Un cycle correspond à une longueur d'onde complète. L'unité de la fréquence, exprimée en cycles par seconde [s−1], est le hertz (Hz). Les multiples courants de cette unité sont le mégahertz (1 MHz = 1 × 106 Hz) et le gigahertz (1 GHz = 1 × 109 Hz).  
 
 L'amplitude correspond à l'ampleur du déplacement de l'onde, ce qui correspond à la moitié de la hauteur entre les pics et les creux. L'amplitude est liée à l'intensité de l'onde, qui est l'intensité lumineuse pour la lumière, et l'intensité sonore pour le son. Le produit de la longueur d'onde d'une onde (λ) et de sa fréquence (ν), &lamda;ν, est la vitesse de l'onde. Ainsi, pour le rayonnement électromagnétique dans le vide, la vitesse est égale à la constante fondamentale, c : 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/974/974_Equations-01.png" style="height: 40px;" />
 
 La longueur d'onde et la fréquence sont inversement proportionnelles : à mesure que la longueur d'onde augmente, la fréquence diminue. Le spectre électromagnétique est la gamme de tous les types de rayonnement électromagnétique.  
 
 Ce texte est adapté de <a href="https://openstax.org/books/chemistry-2e/pages/6-1-electromagnetic-energy">Openstax, Chimie 2e, Section 6.1 : Énergie électromagnétique.</a>

Le caractère ondulatoire de la lumière

La nature de la lumière a fait l’objet d’une enquête depuis l’Antiquité. Au XVIIe siècle, Isaac Newton réalise des expériences avec des lentilles et des prismes...

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measuring light with wavelength and frequency

Light can be described as an electromagnetic wave, and its behavior helps explain many patterns seen in science. For centuries, scientists have tried to understand light. Newton used lenses and prisms to show that white light is made of the colors of the rainbow mixed together. He explained light as tiny particles moving at high speed.

Other scientists, including Christiaan Huygens, showed that reflection and refraction could also be explained by treating light as a wave. At the time, people imagined these waves traveling through a medium called luminiferous aether, which was thought to fill all space. In the early 1800s, Thomas Young showed that light passing through two narrow slits makes an interference pattern. That result fit the wave model much better than the particle model.

James Clerk Maxwell later developed electromagnetic theory and showed that visible light is part of a much larger spectrum of electromagnetic waves. By the end of the nineteenth century, many scientists accepted a split view of the physical world. Matter was described as particles, while electromagnetic radiation was described as waves. These ideas are now called classical mechanics and classical electrodynamics, or classical electromagnetism.

Some experimental results did not fit that classical picture. Scientists first saw them as strange puzzles that might still be solved within the old framework. Those puzzles eventually led to wave-particle duality, a modern idea that links waves and particles at a basic level. This idea replaced the older view.

Electromagnetic radiation matters in chemistry because it can help reveal the energies of electrons in atoms and molecules. It also powers many technologies. Radio waves from a mobile phone, X-rays used by dentists, microwave energy used to cook food, radiant heat from red-hot objects, and the light from a television screen are all forms of electromagnetic radiation. Each of these shows wavelike behavior.

A wave is an oscillation, or repeating motion, that carries energy from one place to another. Rope waves, ripples on water after a pebble falls in, and sound waves from thunder are common examples. In these cases, energy moves through the rope, water, or air while the material itself stays mostly in place. Waves do not have to travel through matter, because electromagnetic waves can move through empty space.

Maxwell showed that electromagnetic waves contain an electric field and a magnetic field that oscillate together. These fields are perpendicular to each other and to the direction the wave travels. In a vacuum, electromagnetic waves move at 2.998 × 10^8 m/s, which is the speed of light, c. Like all waves, they are described by wavelength, frequency, and amplitude.

Wavelength is the distance between two peaks or two troughs. Frequency is the number of wave cycles that pass a point in a given time. Amplitude is the size of the wave’s displacement, which is half the height between a peak and a trough. Amplitude is related to intensity, so for light it affects brightness, and for sound it affects loudness. Wavelength and frequency are linked by the equation λν = speed, so in a vacuum c = λν. As wavelength increases, frequency decreases. Electromagnetic waves span a huge range, from kilometers to picometers, and the full set is called the electromagnetic spectrum.

Measuring Light with Wavelength and Frequency

measuring-light-with-wavelength-and-frequency

the wave nature of light

Light can be described as an electromagnetic wave, and its behavior helps explain many patterns seen in science. For centuries, scientists have tried to understand light. Newton used lenses and prisms to show that white light is made of the colors of the rainbow mixed together. He explained light as tiny particles moving at high speed. Other scientists, including Christiaan Huygens, showed that reflection and refraction could also be explained by treating light as a wave. At the time, people...

the electromagnetic spectrum

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The electromagnetic spectrum includes all electromagnetic radiation arranged by frequency and wavelength. Visible light is only a small part of it, and each color of visible light has its own frequency and wavelength. Different parts of the spectrum also use different units. Radio waves are usually measured in MHz, while the visible range is often measured in nm or angstroms. The spectrum is organized from radio waves to gamma rays as frequency increases and wavelength decreases. Radio waves...

interference and diffraction

Wave Patterns from Light and Slits

Light can form wave patterns through interference and diffraction. When two electromagnetic waves meet with their peaks and troughs lined up, they combine into a larger wave. This is constructive interference, and the waves are in phase. When a peak of one wave meets a trough of the other, the waves reduce each other. This is destructive interference, and the result has a much lower amplitude. Diffraction is another wave behavior. When light passes through a slit that is about the same size as...

photoelectric effect

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the bohr model

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emission spectra

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the de broglie wavelength

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the uncertainty principle

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the quantum-mechanical model of an atom

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quantum numbers

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atomic orbitals

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Electron filling order in atomic orbitals follows the aufbau principle and Hund's rule. To write an electron configuration, we build atoms in order of atomic number. Starting with hydrogen and moving across the periods of the periodic table, one proton is added to the nucleus and one electron is placed into the correct subshell. This process describes the ground-state electron configurations of the elements. The aufbau principle comes from the German word aufbau, which means "to build up." It...

electron configuration of multielectron atoms

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Valence Electrons and Noble Gas Shorthand

Valence electrons and noble gas shorthand help show how electrons are arranged in multielectron atoms. Sodium, the alkali metal with atomic number 11, has one more electron than neon. That extra electron goes into the lowest-energy subshell available, the 3s orbital, so sodium has the configuration 1s2 2s2 2p6 3s1. Electrons in the outermost shell, where n is highest, are called valence electrons. Electrons in the inner shells are called core electrons. Because core electrons often match a...

key terms and concepts

Explore light as an electromagnetic wave, including wavelength, frequency, amplitude, the speed of light, and examples from the electromagnetic spectrum.

Measuring Light with Wavelength and Frequency | JoVE K12

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Pennsylvania State Academic Standards

9-12

Earth and Space Science

Earth's Systems

3.3.9-12.H

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3.3.9-12.B

Weather and Climate

3.3.9-12.E

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Waves and Electromagnetic Radiation

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Earth’s Place In The Universe

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Waves and Their Applications in Technologies for Information Transfer

PHYS.PS4.7

CHEM1.PS4.1

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ES.2

ES.2.a

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HS+C.P1

HS+C.P1U1.2

CHEM.6

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HS-PS4-3

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Florida Department of Education

SC.912.E.5

SC.912.E.5.8

SC.912.P.8

SC.912.P.8.3

SC.912.P.12

SC.912.P.12.7

PHYS.9

PHYS.9.A

PHYS.9.C

PHYS.9.D

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South Carolina College and Career Ready Science Standards

C-PS4-4

P-PS3-3

P-PS4-1

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New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-7.

HS. Waves and Electromagnetic Radiation

HS-PS4-3.

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IPC.7.A

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Physical and Chemical Properties of Matter

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Atomic Radii and Effective Nuclear Charge

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IPC.7.B

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Measuring Light with Wavelength and Frequency

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