Name: radiation pressure in light and space
Uploaded: 2023-09-18T17:11:21.000Z
Duration: 1 min 9 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Place in the Universe

ESS.EES.1.4

Radiation Pressure: Problem Solving

Consideriamo un satellite in orbita attorno alla Terra. La sua distanza dal sole è di 1,5 X 1011 metri. Il sole irradia con una potenza media di 3,8 X 1026 watt.
Se i suoi pannelli solari di raccolta avessero una superficie totale di 20 metri quadrati, quale sarebbe la pressione di radiazione sui pannelli solari e la forza ad essa dovuta?
L'intensità della radiazione solare è uguale alla potenza solare media per unità di superficie. Il suo valore al satellite è quindi di 1,3 X 103 watt per metro quadrato.
Supponendo che i pannelli solari assorbano completamente tutta la luce solare incidente, la pressione di radiazione sui pannelli solari è uguale all'intensità della radiazione solare alla velocità della luce, che è di 4,3 X 10-6 newton per metro quadrato.
La forza di radiazione è il prodotto della pressione di radiazione e dell'area dei pannelli solari. Il suo valore è calcolato in 8,6 X 10-5 newton.

<ol>
	<li>OpenStax. (2019). Fisica universitaria Vol. 2. [Versione web]. Estratto da <a href="https://openstax.org/books/university-physics-volume-2/pages/16-4-momentum-and-radiation-pressure">https://openstax.org/books/university-physics-volume-2/pages/16-4-momentum-and-radiation-pressure</a>; sezione 16.4; pagine 719-721.</li>
	<li>Young, H.D e Freedman, R.A. (2012). Fisica universitaria con fisica moderna. San Francisco, CA: Pearson; sezione 32.4; pagine 1068-1069.</li>
</ol>

pressione di radiazione: risolvere i problemi

La pressione di radiazione applicata da un'onda elettromagnetica su una superficie perfettamente assorbente è uguale alla densità energetica dell'onda. Quando un'onda elettromagnetica viene completamente assorbita da una superficie, il momento dell'onda viene trasferito anche alla superficie stessa. Il tasso a cui viene trasmesso il momento a una superficie assorbente perpendicolare alla direzione di propagazione è uguale alla forza sulla superficie.

Il valore medio del tasso di trasferimento del momento diviso per l'area assorbente rappresenta la forza media per unità di area o la pressione di radiazione dovuta all'onda. Se il materiale è perfettamente riflettente, come una superficie metallica, e l'incidenza avviene lungo la normale alla superficie, allora la pressione esercitata raddoppia perché la direzione del momento si inverte al riflesso.

La luce solare esercita una pressione di radiazione molto più forte all'interno del sole rispetto a quella esercitata sulla Terra. La pressione di radiazione all'interno delle stelle che sono significativamente più massive e luminose del sole è così elevata che aumenta notevolmente la pressione interna del gas, impedendo a queste stelle di collassare a causa della propria gravità. A volte, la pressione di radiazione delle stelle può influenzare significativamente il materiale nelle loro vicinanze immediate.

La pressione di radiazione gioca un ruolo nello spiegare molti altri fenomeni astronomici osservati, inclusa l'apparizione delle comete. Quando una cometa si avvicina al sole, si riscalda, e la sua superficie inizia a evaporare. Alcuni dei gas e della polvere formano code quando lasciano la cometa. Una cometa ha due code; la prima è la coda ionica, composta principalmente da gas ionizzati. Questi ioni interagiscono elettromagneticamente con il vento solare. La forza del vento solare sui gas ionizzati è abbastanza forte da far sì che la coda ionica punti quasi sempre direttamente lontano dal sole.

La seconda coda è composta da particelle di polvere. Poiché la coda di polvere è elettricamente neutra, non interagisce con il vento solare. Tuttavia, questa coda è influenzata dalla pressione di radiazione prodotta dalla luce del sole. Anche se piuttosto debole, questa pressione è abbastanza forte da far deviare la coda di polvere dalla traiettoria della cometa.

Pressione di radiazione: risolvere i problemi

La pressione di radiazione applicata da un'onda elettromagnetica su una superficie perfettamente assorbente è uguale alla densità di energia dell'onda. Lo slancio dell'onda...

Education

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JoVE Core

Physics

Fisica

Unit 1

Unità 1

Electromagnetic Waves

Onde elettromagnetiche

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 strikes it straight on, the pressure doubles. That happens because the momentum changes direction after reflection.

Radiation pressure is much stronger inside the sun than it is on Earth. In stars that are more massive and brighter than the sun, it can greatly increase the internal gas pressure. This extra pressure helps keep those stars from collapsing under their own gravity.

Radiation pressure also helps explain comet tails. As a comet moves close to the sun, it warms up and its surface begins to evaporate. Gas and dust escape and form tails.

A comet has two tails. The ion tail is made mainly of ionized gas, and it interacts with the solar wind. That force is strong enough that the ion tail usually points directly away from the sun. The dust tail is electrically neutral, so it does not interact with the solar wind. Instead, sunlight pushes on it through radiation pressure, and this small force can make the dust tail bend away from the comet’s path.

Radiation Pressure in Light and Space

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...

generating electromagnetic radiations

Hertz's Spark Gaps and Radio Waves

Heinrich Hertz used sparks and tuned circuits to show that electromagnetic waves could be produced in the lab. Starting in 1887, the German physicist ran experiments that confirmed electromagnetic waves exist and travel at the speed of light. Hertz built an alternating-current RLC circuit. RLC stands for resistor, inductor, and capacitor. The circuit was set to a known resonant frequency and connected to a loop of wire. High voltage across the gap in the loop created sparks. Those sparks gave...

the electromagnetic spectrum

Electromagnetic Waves in Everyday Technology

Electromagnetic waves are grouped by wavelength and frequency. This set of waves is called the electromagnetic spectrum. It includes radio waves, microwaves, infrared, visible light, X-rays, and gamma rays. Radio waves have wavelengths from millimeters to kilometers. They are often used for audio communication, such as radios. In many cases, they come from alternating current in the wires of a broadcast antenna. Radio waves also carry AM and FM radio, cellular phone signals, and TV signals. <br...

electromagnetic wave equation

How Maxwell Linked Light to Waves

Maxwell's equations show how electric and magnetic fields behave in a vacuum, or empty space. They are written as differential equations and describe fields created by source charges, whether the charges are still or moving. These fields also act on a test charge, and its motion can be found with the right boundary conditions. The key question in empty space is what happens when there are no source charges. In the vacuum form of Maxwell's four equations, the first-order partial differential...

plane electromagnetic waves i

Transverse Fields in Electromagnetic Waves

Electromagnetic waves are made of electric and magnetic fields that move through space together. Maxwell's equations predict these waves, and they can travel in free space without a medium. The electric field acts on a stationary charge, while the magnetic field acts on a moving charge. For a wave traveling along the x-axis, the fields are written as Ey(x, t) and Bz(x, t). In free space, there are no free charges or currents, so the charge enclosed and current terms in Maxwell's equations are...

plane electromagnetic waves ii

Faraday’s Law in a Plane Wave

Faraday’s law can be used to link the electric and magnetic fields in a plane electromagnetic wave. Here, the wavefront moves in the x-direction at a constant speed. The goal is to show how the field strengths must be related for the wave to stay consistent with Faraday’s law. To apply the law, a rectangle of width a is placed with its area vector in the positive z-direction. The line integral is taken counterclockwise around the rectangle. One side lies outside the wavefront, so the electric...

propagation speed of electromagnetic waves

propagation-speed-of-electromagnetic-waves

Maxwell’s Equations and Light Speed

Electromagnetic waves follow Ampere’s law when there is no conduction current. A plane wavefront moves in the positive x-direction. To analyze it, a rectangle is placed in the xz-plane with its area vector pointing in the positive y-direction. The line integral around the rectangle is taken counterclockwise. The magnetic field is zero on some sides and perpendicular on others. It is parallel to one side, and that side gives a non-zero contribution to the integral. Because the left side of...

electromagnetic waves in matter

How Light Slows in Materials

Electromagnetic waves can travel through matter as well as through vacuum. Light is one example. It can move through air, water, or glass. When an electromagnetic wave passes through a dielectric medium, the equations that describe it change. In Ampere's law, the permittivity of free space, ε0, is replaced by the permittivity of the dielectric, ε. The vacuum permeability, μ0, is also replaced by the permeability of the medium, μ. The wave speed c in vacuum is then replaced by a lower speed, v,...

energy carried by electromagnetic waves

How EM Waves Transfer Energy

Electromagnetic waves transfer energy through their electric and magnetic fields. This energy can be easy to notice, like the warmth from the summer sun, or harder to feel, like the energy in gamma rays that can damage living cells. The fields in an electromagnetic wave can exert forces on charges in a system. They can move those charges and do work on them. Even if a wave is not absorbed right away, it still carries energy away from its source. If some of the wave energy is absorbed, the...

intensity of electromagnetic waves

Poynting Vector and Light Intensity

The Poynting vector describes the energy flux of an electromagnetic wave. It tells how much energy passes through a unit area in a unit time at a specific moment. For a plane electromagnetic wave moving along the x-axis, the energy flux depends on the peak electric field E0 and the peak magnetic field B0. For high-frequency waves, the energy flux changes very quickly with time. Visible light has a frequency on the order of 10^14 Hz, so its energy flux varies too fast to track directly. Most...

momentum and radiation pressure

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...

radiation pressure: problem solving

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...

standing electromagnetic waves

Electromagnetic Wave Reflection at Conductors

Electromagnetic waves can reflect from a conductor or a dielectric. When the reflected wave combines with the incoming wave, the result is a standing electromagnetic wave. This is similar to the standing waves formed on a stretched string. To see how this happens, consider a perfect conductor placed in the yz-plane. A linearly polarized electromagnetic wave moving in the negative x-direction strikes the surface. The electric field cannot have a component parallel to the surface of a perfect...

standing waves in a cavity

Electromagnetic Modes in a Microwave Cavity

Electromagnetic waves can form standing patterns inside a cavity. Household microwaves and lasers are common examples of this effect. When two conducting metal plates are placed parallel at the nodal planes, they create a space where standing waves can exist. The cavity between the plates works like a stretched string fixed at x = 0 and x = L. The distance L must be an integer multiple of half a wavelength. The wavelengths that meet this condition have matching frequencies, and each frequency,...

key terms and concepts

Explore how electromagnetic waves transfer momentum, how reflection changes radiation pressure, and why sunlight shapes star balance and comet tails.

Radiation Pressure in Light and Space | JoVE K12

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JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Pennsylvania State Academic Standards

Earth and Space Science

Earth's Systems

3.3.9-12.H

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-ESS2-4

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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

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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.

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First Law of Thermodynamics

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Energy Dynamics

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Radiation Pressure in Light and Space

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