Name: how light slows in materials
Uploaded: 2023-04-30T12:46:27.000Z
Duration: 1 min 30 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

Physical Science

Waves and Their Applications

PS.PSc.8.2

Electromagnetic Waves in Matter

Im Gegensatz zu mechanischen Wellen können sich elektromagnetische Wellen im Vakuum oder in jedem materiellen Medium ausbreiten.
Betrachten Sie die elektromagnetische Welle, die durch ein dielektrisches Medium fließt. In einem solchen Fall werden die Maxwell-Gleichungen modifiziert.
Im Ampereschen Gesetz wird ε0 durch ε, die Permittivität des Dielektrikums, ersetzt. Außerdem wird die Vakuumdurchlässigkeit durch die Durchlässigkeit des Mediums ersetzt.
Erinnern wir uns an die Beziehungen zwischen den elektrischen und magnetischen Feldern, die mit dem Faradayschen und dem Ampereschen Gesetz abgeleitet wurden. Da die Geschwindigkeit der Welle in einem Dielektrikum nicht die gleiche ist wie in einem Vakuum, wird die Konstante "c" durch eine reduzierte Geschwindigkeit "v" ersetzt.
Durch den Vergleich dieser beiden Beziehungen kann die Geschwindigkeit einer elektromagnetischen Welle in einem Dielektrikum ermittelt werden.
Mit Ausnahme von ferromagnetischen Materialien liegt die relative Permeabilität der meisten Dielektrika in der Regel nahe eins, und die Dielektrizitätskonstante ist immer größer als eins. Daher ist die Wellengeschwindigkeit im Vergleich zur Geschwindigkeit im Vakuum immer geringer.
Das Verhältnis der Geschwindigkeit einer elektromagnetischen Welle im Vakuum zur Geschwindigkeit in einem Material wird als Brechungsindex des Materials bezeichnet.

<ol>
	<li>Young, H.D. und Freedman, R.A. (2012). Universitätsphysik mit moderner Physik. San Francisco, Kalifornien: Pearson. Abschnitt 32.3; Seiten 1063–1064.</li>
</ol>

elektromagnetische wellen in materie

Elektromagnetische Wellen können sich sowohl im Vakuum als auch in Materie bewegen. Zum Beispiel kann sich Licht, das eine elektromagnetische Welle ist, durch Luft, Wasser oder Glas bewegen.

Betrachten wir die elektromagnetische Welle, die durch ein dielektrisches Medium verläuft. In einem solchen Fall werden Maxwells Gleichungen modifiziert. In Ampères Gesetz wird die dielektrische Permittivität des freien Raums ε0 durch die Permittivität des Dielektrikums ε ersetzt. Auch die Vakuumpermeabilität μ0 wird durch die Permeabilität des Mediums μ ersetzt.

Darüber hinaus wird die konstante Geschwindigkeit c in dem Ausdruck für die Beziehungen zwischen elektrischen und magnetischen Feldern, die durch Faradays und Ampères Gesetz abgeleitet wurden, durch eine reduzierte Geschwindigkeit v ersetzt. Durch den Vergleich dieser beiden Beziehungen kann die Geschwindigkeit einer elektromagnetischen Welle in einem Dielektrikum ermittelt werden.

<img alt="Equation1" src="/files/ftp_upload/13825/13825_Equation_1.svg" style="text-align: center; height: 38px;" />

Für die meisten Dielektrika ist die relative Permeabilität μm fast gleich eins, mit Ausnahme der isolierenden ferromagnetischen Materialien. Da die dielektrische Konstante ε immer größer als eins ist, ist die Geschwindigkeit von elektromagnetischen Wellen in einem Dielektrikum immer kleiner als die Geschwindigkeit im Vakuum.

<img alt="Equation2" src="/files/ftp_upload/13825/13825_Equation_2.svg" style="text-align: center; height: 30px;" />

In der Optik wird das Verhältnis der Geschwindigkeit im Vakuum zur Geschwindigkeit in einem Material als Brechungsindex des Materials bezeichnet. Die dielektrische Konstante ist eine Funktion der Frequenz. Zum Beispiel beträgt die dielektrische Konstante für Wasser bei konstanten Feldern 80,4, im Frequenzbereich des sichtbaren Lichts beträgt sie hingegen ungefähr 1,8.

Elektromagnetische Wellen in Materie

Elektromagnetische Wellen können sich sowohl im Vakuum als auch in Materie ausbreiten. Zum Beispiel kann sich Licht, eine elektromagnetische Welle, durch Luft, Wasser, ...

Education

Lehre

JoVE Core

Physics

Physik

Unit 1

Einheit 1

Electromagnetic Waves

Elektromagnetische Wellen

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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, in the relations found from Faraday's law and Ampere's law.

By comparing those relations, the speed of an electromagnetic wave in a dielectric can be found. For most dielectrics, the relative permeability κm is nearly 1. This is not true for insulating ferromagnetic materials. Because the dielectric constant κ is always greater than 1, electromagnetic waves travel more slowly in a dielectric than in vacuum.

In optics, the ratio of the speed in vacuum to the speed in a material is called the refractive index. The dielectric constant also changes with frequency. Water, for example, has a dielectric constant of 80.4 for steady fields, but it is about 1.8 in the visible-light range.

How Light Slows in Materials

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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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...

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plane electromagnetic waves ii

Faraday’s Law in a Plane Wave

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propagation speed of electromagnetic waves

propagation-speed-of-electromagnetic-waves

Maxwell’s Equations and Light Speed

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electromagnetic waves in matter

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

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intensity of electromagnetic waves

Poynting Vector and Light Intensity

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momentum and radiation pressure

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key terms and concepts

Learn how electromagnetic waves travel through dielectrics, why their speed drops below vacuum speed, and how refractive index and dielectric constant are related.

How Light Slows in Materials | 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.

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Waves and Their Applications in Technologies for Information Transfer

PS.Phy.7.1

Pennsylvania State Academic Standards

Waves and Electromagnetic Radiation

3.2.9-12.V

Louisiana Student Standards for Science

High School

Earth Science

Earth’s Place In The Universe

HS-ESS1-1

HS-ESS1-2

Waves And Their Applications In Technologies For Information Transfer

HS-PS4-1

Tennessee Academic Standards

PHYS.PS4.2

Virginia  Standards of Learning

HIgh School

PS.7

PS.7.a

PH.5

PH.5.c

PH.6

PH.6.b

Minnesota Academic Standards in Science

3.2.2 9P.3.1.1.2

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New Jersey Student Learning Standards for Science

HS-PS4-3

HS-PS4-4

Arizona Science Standards

HS.P4

HS.P4U1.10

Alabama Course of Study Science

9-12.PS.2.2.c

9-12.P.3.7.c

Next Generation Science Standards

Texas Essential Knowledge and Skills

PHYS.8

PHYS.8.B

Chemistry and Physics

IPC.6

IPC.6.E

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South Carolina College and Career Ready Science Standards

Chemistry

C-PS4-4

P-PS4-3

Earth and Space Science (ESS)

Earth’s Place in the Universe

E-ESS1-2.

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Waves and Electromagnetic Radiation

HS-PS4-4.

Georgia Standards of Excellence

SPS9.

electromagnetic-waves-and-mechanical-waves

Electromagnetic Waves and Mechanical Waves

SP4.

mechanical-and-electromagnetic-waves-properties

Mechanical and Electromagnetic Waves Properties

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Equations of Wave Motion

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Graphing the Wave Function

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Speed of a Transverse Wave

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Energy and Power of a Wave

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Carry out investigations to explain the quantitative and qualitative relationships among wave frequency, wave velocity, wavelength, and wave energy.

PS.PSc.8.1

James Clerk Maxwell formulated a single theory combining all the electric and magnetic effects scientists knew during that time, calling the phenomena his ...

Electromagnetic Wave Equation

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Propagation Speed of Electromagnetic Waves

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Energy Carried By Electromagnetic Waves

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Intensity Of Electromagnetic Waves

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Interference and Superposition of Waves

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Reflection of Waves

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Propagation of Waves

When a wave propagates from one medium to another, part of it may get reflected in the first medium, and part of it may get transmitted to the second ...

Sound Waves: Interference

Sound waves can be modeled either as longitudinal waves, wherein the molecules of the medium oscillate around an equilibrium position, or as pressure ...

Interference: Path Lengths

Consider two sources of sound, that may or may not be in phase, emitting waves at a single frequency, and consider the frequencies to be the same.
Two ...

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Use models to explain the wave interactions of reflection, refraction, diffraction, and interference.

PS.PSc.8.3

Standing Waves

Sometimes waves do not seem to move; rather, they just vibrate in place. Unmoving waves can be seen on the surface of a glass of milk kept in a ...

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Modes of Standing Waves - I

A close look at earthquakes provides evidence for the conditions appropriate for resonance, standing waves, and constructive and destructive interference. ...

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Modes of Standing Waves: II

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Obtain, evaluate, and communicate information to explain how instruments that transmit and detect waves are used in everyday life.

PS.PSc.8.4

Analyze the nature of waves and their applications.

How Light Slows in Materials

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