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

גלים אלקטרומגנטיים מעבירים תנע תוך כדי נסיעה בחלל. צפיפות התנע המתאימה מתבטאת במונחים של גודל וקטור פוינטינג ומהירות האור.
על ידי החלפת הנפח שנכבש על ידי הגל העובר באזור במרווח זמן קצר, ניתן לקבל את קצב זרימת התנע ליחידת שטח.
הקצב הממוצע של העברת תנע ליחידת שטח מתקבל על ידי החלפת הערך הממוצע של וקטור פוינטינג בעוצמה.
בשל העברת התנע, גלים אלקטרומגנטיים מפעילים לחץ על פני השטח, המכונה לחץ קרינה.
כעת, קצב השינוי הממוצע של התנע שווה לכוח הממוצע ולכוח ליחידת שטח הוא לחץ הקרינה.
לפיכך, לחץ הקרינה עומד ביחס ישר לעוצמת הגל.
אם המשטח סופג בצורה מושלמת את הגל האלקטרומגנטי, התנע המתאים מועבר גם הוא לחלוטין אל פני השטח.
עבור משטח המשקף באופן מושלם, שינוי המומנטום יהיה כפול. לפיכך, גם לחץ הקרינה מוכפל.

<ol>
	<li>OpenStax. (2019). פיזיקה אוניברסיטאית כרך 2. [גרסת אינטרנט]. מקור: <a href="https://openstax.org/books/university-physics-volume-2/pages/16-4-momentum-and-radiation-pressure">16.4 תנע ולחץ קרינה - פיזיקה אוניברסיטאית כרך 2 | OpenStax</a></li>
</ol>

מומנטום ולחץ קרינה

<div style="direction:rtl">עצם הסופג גל אלקטרומגנטי יחווה כוח בכיוון התפשטות הגל. כוח זה מתרחש מכיוון שגלים אלקטרומגנטיים מכילים ומעבירים מומנטום. הכוח אחראי ללחץ הקרינה של הגל המופעל על העצם. התחזית של מקסוול אושרה בשנת 1903 על ידי ניקולס והאל על ידי מדידה מדויקת של לחצי קרינה עם איזון פיתול. למכשיר המדידה היו מראות תלויות מסיב שנשמר בתוך מיכל זכוכית. ניקולס והאל השיגו סטייה קלה למדידה של המראות מהאיר אור על אחת מהן. מתוך הסטייה הנמדדת, הם חישבו את הכוח הלא מאוזן על המראה וקיבלו הסכמה עם הערך החזוי של הכוח. לחץ הקרינה המופעל על ידי גל אלקטרומגנטי על משטח סופג בצורה מושלמת מתגלה כשווה לצפיפות האנרגיה של הגל. נניח שהחומר משתקף בצורה מושלמת, והגלים האלקטרומגנטיים יורדים נורמליים לפני השטח. במקרה זה, הלחץ המופעל גדול פי שניים מכיוון שכיוון המומנטום מתהפך בהשתקפות. לחץ הקרינה ממלא תפקיד בהסבר של תופעות אסטרונומיות רבות שנצפו, כולל הופעת שביטים. כשכוכב שביט מתקרב לשמש, הוא מתחמם, ופני השטח שלו, המורכבים מגזים קפואים וחלקיקי סלע ואבק, מתאדים. תרדמת השביט היא האזור המעורפל סביבו המורכב מהגזים והאבק. חלק מהגזים והאבק יוצרים זנבות כשהם עוזבים את השביט. זנב היונים מורכב בעיקר מגזים מיוננים. יונים אלה מקיימים אינטראקציה אלקטרומגנטית עם רוח השמש, זרם רציף של חלקיקים טעונים הנפלטים מהשמש. כוחה של רוח השמש על הגזים המיוננים חזק מספיק כדי שזנב היונים כמעט תמיד יצביע ישירות מהשמש. הזנב השני מורכב מחלקיקי אבק. מכיוון שזנב האבק הוא ניטרלי מבחינה חשמלית, הוא אינו יוצר אינטראקציה עם רוח השמש. עם זאת, זנב זה מושפע מלחץ הקרינה שמייצר האור מהשמש. למרות שהוא קטן יחסית, לחץ זה חזק מספיק כדי לגרום לעקירת זנב האבק מנתיב השביט.</div>

עצם הבולע גל אלקטרומגנטי יחווה כוח בכיוון ההתפשטות של הגל. כוח זה מתרחש מכיוון ש...

Education

JoVE Core

Physics

פיזיקה

Unit 1

יחידה 1

Electromagnetic Waves

גלי אלקטרומגנטיים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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...

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 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...

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 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 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.

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

HS-PS4-4.

What is Climate?

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Global Climate Change

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The Electromagnetic Spectrum

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Mechanisms of Heat Transfer II

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Students who demonstrate understanding can analyze geoscience data to make the claim that one change to Earth's surface can create feedback that causes changes to other Earth systems.  Clarification Statement: Examples should include climate feedbacks, such as how an increase in greenhouse gases causes a rise in global temperatures that melts glacial ice, which reduces the amount of sunlight reflected from Earth's surface, increasing surface temperatures and further reducing the amount of ice.  Examples could also be taken from other system interactions, such as how the loss of ground vegetation causes an increase in water runoff and soil erosion;  how dammed rivers increase groundwater recharge, decrease sediment transport, and increase coastal erosion;  or how the loss of wetlands causes a decrease in local humidity that further reduces the wetland extent.  Assessment Boundary:

Igneous Intrusive Rock

Source: Laboratory of Alan Lester - University of Colorado Boulder
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Igneous Volcanic Rock

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Making a Geologic Cross Section

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Conditions on Early Earth

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Radioactive Decay and Radiometric Dating

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Types of Radioactivity

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Alpha (&#945;) decay is the ...

Nuclear Power

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Isotopes and Radioisotopes

In the early 1900s, English chemist Frederick Soddy realized that an element could have atoms with different masses that were chemically ...

Nuclear Fusion

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Nuclear Transmutation

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determining-spatial-orientation-rock-layers-with-brunton

Determining Spatial Orientation of Rock Layers with the Brunton Compass

Source: Laboratory of Alan Lester - University of Colorado Boulder
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Dynamics of Structures

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Students who demonstrate understanding can develop a model based on evidence of Earth's interior to describe the cycling of matter by thermal convection.  Clarification Statement: Emphasis is on both a one-dimensional model of Earth, with radial layers determined by density, and a three-dimensional model, which is controlled by mantle convection and the resulting plate tectonics.  Examples of evidence include maps of Earth's three-dimensional structure obtained from seismic waves, records of the rate of change of Earth's magnetic field (as constraints on convection in the outer core), and identification of the composition of Earth's layers from high-pressure laboratory experiments.  Assessment Boundary:

3.3.9-12.I

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physical-and-chemical-properties-of-matter

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Solvents

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Adhesion

Adhesion occurs when one type of molecule is attracted to a different molecule. Water exhibits adhesive properties in the presence of polar surfaces, such ...

Students who demonstrate understanding can plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes. [cite: 44] Clarification Statement: Emphasis is on mechanical and chemical investigations with water and a variety of solid materials to provide the evidence for connections between the hydrologic cycle and system interactions commonly known as the rock cycle. [cite: 45] Examples of mechanical investigations include stream transportation and deposition using a stream table, erosion using variations in soil moisture content, or frost wedging by the expansion of water as it freezes. [cite: 46] Examples of chemical investigations include chemical weathering and recrystallization (by testing the solubility of different materials) or melt generation (by examining how water lowers the melting temperature of most solids). [cite: 47] Assessment Boundary:

3.3.9-12.K

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3.3.9-12.L

Radiation Pressure in Light and Comets

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