Name: radiation pressure in light and comets
Uploaded: 2023-04-30T12:46:50.000Z
Duration: 1 min 20 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Earth's Systems

3.3.9-12.H

Momentum And Radiation Pressure

As ondas eletromagnéticas transportam impulso enquanto viajam pelo espaço. A densidade de momento correspondente é expressa em termos da magnitude do vetor de Poynting e da velocidade da luz.
Substituindo o volume ocupado pela onda que passa por uma área em um curto intervalo de tempo, pode-se obter a vazão de momento por unidade de área.
A taxa média de transferência de momento por unidade de área é obtida substituindo o valor médio do vetor de Poynting pela intensidade.
Devido à transferência de momento, as ondas eletromagnéticas exercem pressão na superfície, conhecida como pressão de radiação.
Agora, a taxa média de variação do momento é igual à força média e a força por unidade de área é a pressão de radiação.
Assim, a pressão de radiação é diretamente proporcional à intensidade da onda.
Se a superfície absorver perfeitamente a onda eletromagnética, o momento correspondente também é transferido completamente para a superfície.
Para uma superfície perfeitamente refletora, a mudança de momento será dupla. Assim, a pressão de radiação também dobra.

<ol>
	<li>OpenStax. (2019). Física Universitária Vol. 2. [Versão Web]. Obtido de <a href="https://openstax.org/books/university-physics-volume-2/pages/16-4-momentum-and-radiation-pressure">16.4 Momento e Pressão de Radiação - University Physics Volume 2 | OpenStax</a></li>
</ol>

momento e pressão de radiação

Um objeto que absorve uma onda eletromagnética experimentaria uma força na direção de propagação da onda. Essa força ocorre porque as ondas eletromagnéticas contêm e transportam momento. A força representa a pressão de radiação da onda exercida sobre o objeto. A previsão de Maxwell foi confirmada em 1903 por Nichols e Hull, que mediram precisamente as pressões de radiação com uma balança de torção. O instrumento de medição continha espelhos suspensos em uma fibra mantidos dentro de um recipiente de vidro. Nichols e Hull obtiveram uma leve deflexão mensurável dos espelhos ao incidir luz em um deles. A partir da deflexão medida, eles calcularam a força não equilibrada sobre o espelho e obtiveram concordância com o valor previsto. A pressão de radiação aplicada por uma onda eletromagnética em uma superfície perfeitamente absorvente acaba sendo igual à densidade de energia da onda. Suponha que o material seja perfeitamente refletor e as ondas eletromagnéticas incidam normalmente na superfície. Nesse caso, a pressão exercida é o dobro, porque a direção do momento se inverte ao refletir.

A pressão de radiação desempenha um papel na explicação de muitos fenômenos astronômicos observados, incluindo o aparecimento de cometas. Quando um cometa se aproxima do Sol, ele se aquece e sua superfície, composta de gases congelados e partículas de rocha e poeira, evapora. A coma do cometa é a área nebulosa ao seu redor composta pelos gases e poeira. Alguns dos gases e poeira formam caudas quando deixam o cometa. A cauda iônica é composta principalmente por gases ionizados. Esses íons interagem eletromagneticamente com o vento solar, que consiste de um fluxo contínuo de partículas carregadas emitidas pelo Sol. A força do vento solar sobre os gases ionizados é tão forte que a cauda iônica quase sempre aponta diretamente para longe do Sol. A segunda cauda é composta por partículas de poeira. Como a cauda de poeira é eletricamente neutra, ela não interage com o vento solar. No entanto, essa cauda é afetada pela pressão de radiação produzida pela luz Solar. Embora relativamente pequena, essa pressão é forte o suficiente para fazer com que a cauda de poeira seja desviada do caminho do cometa.

Momento E Pressão de Radiação

Um objeto absorvendo uma onda eletromagnética experimentaria uma força na direção da propagação da onda. Essa força ocorre porque ...

Education

JoVE Core

Physics

Física

Unit 1

Unidade 1

Electromagnetic Waves

Ondas Eletromagnéticas

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

radiation pressure in light and comets

Radiation pressure is the force that electromagnetic waves can exert on matter. It appears because light carries momentum, so an object that absorbs a wave feels a push in the direction the wave travels. This same force helps explain why sunlight can affect small particles in space.

Maxwell predicted radiation pressure, and Nichols and Hull confirmed it in 1903. They used a torsion balance with mirrors suspended from a fiber inside a glass container. When they shone light on one mirror, the mirrors shifted slightly. From that tiny deflection, they calculated the unbalanced force and found agreement with the predicted value.

The size of the pressure depends on the surface. For a perfectly absorbing surface, the radiation pressure equals the energy density of the wave. For a perfectly reflecting surface with the wave hitting straight on, the pressure is twice as large because the light reverses momentum when it reflects.

Radiation pressure also helps explain comet tails. When a comet nears the Sun, it warms up and releases frozen gases, rock, and dust. This forms a coma, which is the hazy cloud around the comet, and it can also create tails.

The ion tail is made mostly of ionized gases. These ions interact with the solar wind, a stream of charged particles from the Sun, and the tail usually points away from the Sun. The dust tail is different. It contains neutral dust, so it does not respond to the solar wind. Instead, sunlight’s radiation pressure pushes the dust tail away from the comet’s path.

Radiation Pressure in Light and Comets

electromagnetic waves

Maxwell’s Equations Behind EM Waves

Maxwell’s equations explain how electric and magnetic fields work together to create electromagnetic waves. James Clerk Maxwell brought together the ideas of Oersted, Coulomb, Gauss, and Faraday and built a single theory of electromagnetism. Together with the Lorentz force law, his equations describe the laws of electricity and magnetism. A key part of Maxwell’s work is the symmetry in the equations. Faraday’s law shows that a changing magnetic field produces an electric field. Maxwell added...

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momentum and radiation pressure

Radiation pressure is the force that electromagnetic waves can exert on matter. It appears because light carries momentum, so an object that absorbs a wave feels a push in the direction the wave travels. This same force helps explain why sunlight can affect small particles in space. Maxwell predicted radiation pressure, and Nichols and Hull confirmed it in 1903. They used a torsion balance with mirrors suspended from a fiber inside a glass container. When they shone light on one mirror, the...

radiation pressure: problem solving

Radiation Pressure in Light and Space

Radiation pressure is the push that light can exert on matter. When an electromagnetic wave is completely absorbed by a surface, its energy density is transferred as momentum to that surface. The rate of momentum transfer on a surface perpendicular to the wave gives the force, and the force per unit area is the radiation pressure. A perfectly absorbing surface receives this pressure directly from the incoming wave. If the surface is perfectly reflecting, such as a metal surface, and the light...

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key terms and concepts

Explore how light carries momentum, creates radiation pressure, and was measured by Nichols and Hull. See how it helps shape comet tails.

Radiation Pressure in Light and Comets | JoVE K12

physics

JoVE Core - Fisica apresenta a teoria e a aplicação de tópicos fundamentais da física, incluindo cinemática, dinâmica, mecânica dos fluidos, estática, ondas e acústica, com vídeos animados concisos e de fácil compreensão. Além disso, os vídeos de cientistas em ação demonstram a aplicação de conceitos relacionados em experimentos de pesquisa clássica e original realizados nos laboratórios de todo o mundo hoje em dia.

Weather and Climate

3.3.9-12.E

Physical Science

Waves and Electromagnetic Radiation

3.2.9-12.V

Louisiana Student Standards for Science

High School

Earth Science

Earth’s Systems

HS-ESS2-1

HS-ESS2-4

waves-and-their-applications-in-technologies-for-information-transfer

Waves And Their Applications In Technologies For Information Transfer

HS-PS4-1

Virginia  Standards of Learning

HIgh School

PS.7

PS.7.a

Alabama Course of Study Science

Waves and Their Applications in Technologies for Information Transfer

9-12.PS.2.2.e

9-12.P.3.7.c

Florida Department of Education

SC.912.P.10

SC.912.P.10.19

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

South Carolina College and Career Ready Science Standards

P-PS4-4

Earth and Space Science (ESS)

Earth’s Place in the Universe

E-ESS1-2.

E-ESS2-4.

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Waves and Electromagnetic Radiation

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3.3.9-12.L

Radiation Pressure in Light and Comets

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