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

A luz do sol, as micro-ondas utilizadas para cozinhar alimentos, e as ondas de rádio emitidas por roteadores wi-fi são exemplos de radiação eletromagnética. A radiação eletromagnética é a transmissão da energia que provém do movimento de partículas carregadas de eletricidade. Este movimento cria campos elétricos e magnéticos de oscilação perpendicular que se propagam pelo espaço sob a forma de ondas.Como todas as ondas, as ondas eletromagnéticas são caracterizadas pela sua amplitude, comprimento da onda e frequência. A amplitude do pico é a distância desde a linha média até ao pico ou à calha de uma onda. Determina a intensidade da onda.Por exemplo, a amplitude da luz visível está relacionada com o seu brilho;quanto maior a amplitude, mais brilhante ou mais intensa é a luz. O comprimento da onda é a distância entre pontos idênticos em ondas adjacentes, tais como os picos sucessivos ou calhas;é simbolizado pela letra grega lambda. A radiação eletromagnética pode ser dividida por comprimento da onda, que pode variar entre quilômetros e picômetros.Por exemplo, a variedade de comprimentos das ondas de luz visível é entre 400 e 750 nanometros, que correspondem à luz violeta e vermelha, respetivamente. A frequência, que é simbolizada pela letra grega nu, é o número de ciclos de ondas que passam por um ponto de referência num segundo e é medida em hertz ou ciclos por segundo. O comprimento da onda é a largura de um ciclo.A velocidade de uma onda é o produto da sua frequência e comprimento da onda. Assim, a frequência de uma onda é diretamente proporcional à velocidade em que a onda está a viajar. No entanto, é inversamente proporcional ao comprimento da onda.Portanto, ondas com comprimentos longos, tais como ondas de rádio, têm frequências baixas. Estas ondas são menos enérgicas do que as ondas com altas frequências e comprimentos de onda curtos, tais como os raios gama.

a natureza ondulatória da luz

A natureza da luz tem sido um assunto de investigação desde a antiguidade. No século XVII, Isaac Newton realizou experiências com lentes e prismas e foi capaz de demonstrar que a luz branca consiste na combinação das cores individuais do arco-íris. Newton explicou as suas descobertas ópticas em termos de uma visão "corpuscular" da luz, na qual a luz era composta por correntes de partículas extremamente pequenas que viajavam a altas velocidades de acordo com as leis de movimento de Newton. 

Outros no século XVII, como Christiaan Huygens, mostraram que fenómenos ópticos como reflexão e refração poderiam ser igualmente bem explicados em termos de luz como ondas que viajam a alta velocidade através de um meio chamado "éter luminífero" que se pensava permear todo o espaço. No início do século XIX, Thomas Young demonstrou que a luz que passa por aberturas estreitas e próximas produzia padrões de interferência que não podiam ser explicados em termos de partículas Newtonianas, mas que poderiam ser facilmente explicados em termos de ondas. Mais tarde no século XIX, depois de James Clerk Maxwell ter desenvolvido a sua teoria da radiação eletromagnética e mostrado que a luz era a parte visível de um vasto espectro de ondas eletromagnéticas, a visão particular da luz tornou-se completamente desacreditada. 

No final do século XIX, os cientistas viam o universo físico como contendo aproximadamente dois domínios separados: matéria composta por partículas que se movem de acordo com as leis de movimento de Newton, e radiação eletromagnética que consiste em ondas governadas pelas equações de Maxwell. Hoje, esses domínios são referidos como mecânica clássica e eletrodinâmica clássica (ou eletromagnetismo clássico). Embora houvesse alguns fenómenos físicos que não podiam ser explicados neste quadro, os cientistas nessa altura estavam tão confiantes da solidez global deste quadro que encaravam estas aberrações como paradoxos intrigantes que, em última análise, seriam resolvidos de alguma forma dentro deste quadro. Estes paradoxos conduziram a um quadro contemporâneo que liga intimamente partículas e ondas a um nível fundamental chamado dualidade onda-partícula, que substituiu a visão clássica.

A luz visível e outras formas de radiação eletromagnética desempenham papéis importantes na química, uma vez que podem ser usadas para inferir as energias de eletrões dentro de átomos e moléculas. Grande parte da tecnologia moderna baseia-se na radiação eletromagnética. Por exemplo, as ondas de rádio de um telemóvel, os raios X utilizados por dentistas, a energia utilizada para cozinhar alimentos no microondas, o calor radiante de objetos de um vermelho quente, e a luz do ecrã da sua televisão são formas de radiação eletromagnética que apresentam um comportamento ondulatório.

<h4>Ondas</h4>

Uma onda é uma oscilação ou movimento periódico que pode transportar energia de um ponto no espaço para outro. Exemplos comuns de ondas estão em toda a nossa volta. Agitar a extremidade de uma corda transfere a energia da sua mão para a outra extremidade da corda, deixar cair uma pedra em uma lagoa causa ondulação ao longo da superfície da água, e a expansão do ar que acompanha um raio gera ondas sonoras (trovões) que podem viajar por vários quilómetros. Em cada um destes casos, a energia cinética é transferida através da matéria (corda, água, ou ar), enquanto que a matéria permanece essencialmente no lugar. 

As ondas não precisam estar restringidas a percorrer através da matéria. Como mostrou Maxwell, as ondas eletromagnéticas consistem em um campo elétrico que oscila a passo com um campo magnético perpendicular, ambos perpendiculares à direção de deslocamento. Estas ondas podem percorrer um vácuo a uma velocidade constante de 2,998 × 108 m/s, a velocidade da luz (indicada por c).

Todas as ondas, incluindo formas de radiação eletromagnética, são caracterizadas por um comprimento de onda (indicado por λ, a letra Grega lambda minúscula), uma frequência (indicada por ν, a letra Grega minúscula nu), e uma amplitude. 

O comprimento de onda é a distância entre dois picos ou vales consecutivos em uma onda (medida em metros no sistema SI). As ondas eletromagnéticas têm comprimentos de onda que se situam dentro de um enorme alcance - comprimentos de onda de quilómetros (103 m) a picómetros (10−12 m) foram observados. A frequência é o número de ciclos de onda que passam um ponto específico no espaço em um determinado período de tempo (no sistema SI, isto é medido em segundos). Um ciclo corresponde a um comprimento de onda completo. A unidade de frequência, expressa em ciclos por segundo [s−1], é o hertz (Hz). Múltiplos comuns desta unidade são o megahertz (1 MHz = 1 × 106 Hz) e o gigahertz (1 GHz = 1 × 109 Hz). 

A amplitude corresponde à magnitude do deslocamento da onda, o que corresponde a metade da altura entre os picos e os vales. A amplitude está relacionada com a intensidade da onda, que para a luz é a luminosidade, e para o som é a intensidade sonora. O produto do comprimento de onda de uma onda (λ) com a sua frequência (ν), λν, é a velocidade da onda. Assim, para a radiação eletromagnética em um vácuo, a velocidade é igual à constante fundamental, c:

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/974/974_Equations-01.png" style="height: 40px;" />

O comprimento de onda e a frequência são inversamente proporcionais: À medida que o comprimento de onda aumenta, a frequência diminui. O espectro eletromagnético é o intervalo de todos os tipos de radiação eletromagnética. 

Este texto foi adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/6-1-electromagnetic-energy">Openstax, Chemistry 2e, Section 6.1: Electromagnetic Energy.</a>

A Natureza Ondulatória da Luz

A natureza da luz tem sido objeto de investigação desde a antiguidade. No século XVII, Isaac Newton realizou experimentos com lentes e prismas ...

Education

JoVE Core

Chemistry

Química

Electronic Structure of Atoms

Estrutura Eletrônica dos Átomos

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

Electromagnetic Waves: Uses Across the Spectrum

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

Why Light Ejects Electrons from Metals

Light can eject electrons from a metal surface when it has the right frequency. This process is called the photoelectric effect. Each metal has its own threshold frequency, which is the minimum light frequency needed to free electrons. Light below the threshold frequency cannot cause emission, even if it is very bright. When the light frequency is above the threshold, electrons are ejected. In that case, the number of electrons released is directly proportional to the intensity, or brightness,...

the bohr model

Bohr’s Quantized Atomic Orbits

Bohr’s quantized atomic orbits explain why hydrogen atoms can stay stable. Early in the twentieth century, Ernest Rutherford and his colleagues described atoms as tiny dense nuclei with lighter electrons moving around them. This picture was called the planetary model because it compared the atom to a miniature solar system, with electrons orbiting the nucleus like planets around the sun. The simplest atom is hydrogen. It has one proton in the nucleus and one electron moving around it. In the...

emission spectra

Line Spectra from Heated Gases

Line spectra are produced when heated gases give off light at specific wavelengths. In contrast, hot solids, liquids, or condensed gases radiate excess energy as a continuous spectrum. That spectrum contains an unbroken range of wavelengths. A gas at low partial pressure can produce a line spectrum when it is excited by an electric current or heated. Fluorescent light bulbs and neon signs work in this way. Each element has its own characteristic set of lines, and molecules can also produce...

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Electron waves and standing orbits explain how tiny particles can behave like waves. Large objects in the macroscopic world, like a billiard ball on a table, follow classical physics. A ball keeps moving in a straight line unless it hits another ball or a force such as friction acts on it. It also has a well-defined position, velocity, and momentum, where momentum is mass times velocity. Waves behave differently from macroscopic particles. When waves interact, they can form interference...

the uncertainty principle

Electron Position and Momentum Limits

Heisenberg’s uncertainty principle sets a limit on how precisely we can know an electron’s position and momentum at the same time. Momentum is the motion of a particle, and the two measurements affect each other. If the momentum is known more accurately, the position becomes less certain, and the reverse is also true. Heisenberg described this limit with an equation that uses Planck’s constant. The equation shows the smallest possible uncertainty for position and momentum together. It explains...

the quantum-mechanical model of an atom

Electron Orbitals in Quantum Mechanics

Quantum mechanics explains how electrons behave in atoms using waves and probability. Erwin Schrödinger built on de Broglie’s idea that an electron in hydrogen could act like a circular standing wave instead of moving in fixed circular paths. He then derived the Schrödinger equation, which became a major step in modern atomic theory. When Schrödinger applied his equation to hydrogen-like atoms, it matched Bohr’s energy expression and the Rydberg formula for hydrogen spectra. He described...

quantum numbers

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Electron orbitals are described by quantum numbers that show where an electron is most likely to be found around the nucleus. These numbers come from the quantum mechanical model, which is based on solutions of the Schrödinger equation. They also help explain why electron energy comes in set values instead of changing smoothly. The principal quantum number, n, labels the energy level. It can be 1, 2, 3, and so on, and higher n values usually mean higher electron energy. This number also tells...

atomic orbitals

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Electron regions in atomic orbitals show where an electron is most likely to be found in an atom. These three-dimensional regions are often drawn as boundary surfaces around the densest part of the cloud. The shape of an orbital depends on the angular momentum quantum number, l. This value can range from 0 to n - 1, where n is the principal quantum number. For n = 1, only l = 0 is allowed. For n = 2, both l = 0 and l = 1 are allowed. Orbitals with the same value of l form a subshell. The l =...

the pauli exclusion principle

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Electron spin and orbital pairing explain why only two electrons can fit in one atomic orbital. Electron configuration describes how electrons are arranged in an atom’s orbitals. It is written with three parts: the principal quantum number, n, the orbital type, or subshell, and a superscript that shows how many electrons are in that subshell. For example, 2p4 means four electrons in a p subshell with n = 2, and 3d8 means eight electrons in a d subshell with n = 3. The three quantum numbers...

the energies of atomic orbitals

Shielding and Orbital Penetration

Shielding and orbital penetration help explain why electrons in an atom have different energies. Electrons are attracted to the positive nucleus, but they also repel one another in atoms with more than one electron. The strength of these forces depends on the charge and the distance between the particles. Opposite charges attract, like charges repel, and the force gets weaker as the particles move farther apart. An electron that stays closer to the nucleus is held more tightly. That means...

the aufbau principle and hund's rule

Electron Filling Order in Atomic Orbitals

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

electron-configuration-of-multielectron-atoms

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

chemistry

JoVE Core - Química dá vida a conceitos gerais de química usando vídeos de animação fáceis de entender. Além disso, nos vídeos Cientistas em ação, demonstramos experimentos de pesquisa clássicos e originais realizados atualmente por cientistas em laboratórios em todo o mundo.

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Earth's Systems

3.3.9-12.H

Space Systems

3.3.9-12.B

Weather and Climate

3.3.9-12.E

Physical Science

Waves and Electromagnetic Radiation

3.2.9-12.X

Louisiana Student Standards for Science

Earth Science

Earth’s Place In The Universe

HS-ESS1-1

HS-ESS1-2

Earth’s Systems

HS-ESS2-4

Energy

HS-PS3-3

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Ohio’s Learning Standards and Model Curriculum

Physics

Waves

Light phenomena

Tennessee Academic Standards

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Waves and Their Applications in Technologies for Information Transfer

PHYS.PS4.7

CHEM1.PS4.1

Virginia  Standards of Learning

HIgh School

ES.2

ES.2.a

Arizona Science Standards

HS+C.P1

HS+C.P1U1.2

CHEM.6

CHEM.6.C

Alabama Course of Study Science

Matter and Its Interactions

9-12.C.1.1.c

Earth's Place in the Universe

9-12.ESS.1.2

9-12.ESS.1.2.a

9-12.ESS.1.2.b

Next Generation Science Standards

HS-PS4-1

HS-PS4-3

Earth’s Place in the Universe

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

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS4-4

P-PS3-3

P-PS4-1

new-york-state-science-learning-standards

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.B

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Measuring Light with Wavelength and Frequency

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