Name: electromagnetic wave reflection at conductors
Uploaded: 2023-09-18T17:11:17.000Z
Duration: 1 min 15 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Physical Science

PS.7

PS.7.a

Standing Electromagnetic Waves

Przypomnij sobie fale stojące uformowane w ciasny sznurek. 
Fale stojące to połączenie dwóch fal, które poruszają się w przeciwnym kierunku, ale mają tę samą amplitudę i częstotliwość.
Weźmy pod uwagę idealny arkusz przewodzący umieszczony w płaszczyźnie y-z. Liniowo spolaryzowana fala elektromagnetyczna uderza w arkusz, przemieszczając się w ujemnym kierunku x.
Fala padająca indukuje prąd na powierzchni przewodnika, powodując powstanie dodatkowych pól elektrycznych, wytwarzających falę odbitą o tej samej częstotliwości i amplitudzie co fala padająca.
Nakładanie się na siebie tych dwóch fal generuje falę stojącą. Upraszczając te wyrażenia, podaj punkty na fali, w których wielkości pola elektrycznego i pola magnetycznego wynoszą zero. Są to tak zwane węzły lub płaszczyzny węzłowe.
Antywęzeł to punkt, w którym amplituda przechodzi od maksymalnego dodatniego do maksymalnego ujemnego przemieszczenia.
Węzły pola elektrycznego pokrywają się z antywęzłami pól magnetycznych i odwrotnie. W związku z tym są one przesunięte w fazie o 90 stopni w każdym punkcie.

<ol>
	<li>Young, H.D. i Freedman, R.A. (2012). Fizyka uniwersytecka z fizyką współczesną. San Francisco, Kalifornia: Pearson. Sekcja 32.5; strony 1069–1070.</li>
</ol>

stałe fale elektromagnetyczne

Fale elektromagnetyczne mogą się odbijać; powierzchnia przewodnika lub dielektryka może działać jak reflektor. Podobnie jak pola elektryczne i magnetyczne podlegają zasadzie superpozycji, podobnie jest z falami elektromagnetycznymi. Superpozycja fali padającej i odbitej fali elektromagnetycznej tworzy falę stojącą analogiczną do fal stojących tworzonych na naciągniętej strunie.

Załóżmy, że arkusz doskonałego przewodnika jest umieszczony w płaszczyźnie yz i uderza w niego spolaryzowana liniowo fala elektromagnetyczna przemieszczająca się w kierunku ujemnym x. Ponieważ pole elektryczne nie może mieć składowej równoległej do powierzchni doskonałego przewodnika, pole elektryczne musi wynosić zero w każdym miejscu płaszczyzny yz. Pole elektryczne padającej fali elektromagnetycznej nie jest zawsze równe zeru w płaszczyźnie yz, ale ta fala padająca indukuje prądy oscylacyjne na powierzchni przewodnika, powodując powstanie dodatkowego pola elektrycznego . Wypadkowe pole elektryczne, które jest sumą wektorów tego pola i pola padającego, wynosi zero wszędzie wewnątrz i na powierzchni przewodnika. Prądy indukowane na powierzchni przewodnika wytwarzają również falę odbitą, która wychodzi z płaszczyzny. Zasada superpozycji stwierdza, że całkowite pole w dowolnym punkcie jest sumą wektorową pól elektrycznych fal padających i odbitych, podobnie jak pole magnetyczne. Superpozycja fal padających i odbitych generuje fale stojące.

<img alt="Równanie1" src="/files/ftp_upload/13829/13829_Equation_1.png" style="text-align: center; height: 24px;" />

<img alt="Równanie2" src="/files/ftp_upload/13829/13829_Equation_2.png" style="text-align: center; height: 22px;" />

Uproszczenie tych wyrażeń pozwala uzyskać punkty na fali, w których natężenia pola elektrycznego i magnetycznego wynoszą zero. Nazywa się je węzłami lub płaszczyznami węzłowymi. W połowie drogi pomiędzy dowolnymi dwoma sąsiednimi płaszczyznami węzłowymi znajdują się płaszczyzny o maksymalnej amplitudzie; to są płaszczyzny antynodalne.

Całkowite pole elektryczne jest funkcją sinusową, a całkowite pole magnetyczne jest funkcją cosinus. Dlatego sinusoidalne zmiany obu pól są w każdym punkcie przesunięte w fazie. Węzły pola elektrycznego pokrywają się z antywęzłami pól magnetycznych i odwrotnie. Zatem wynoszą one 90″ poza fazą w każdym punkcie. Inaczej jest w przypadku fali przemieszczającej się w jednym kierunku, w przypadku której sinusoidalne zmiany pól elektrycznych i magnetycznych w dowolnym punkcie są zgodne w fazie.

Stałe fale elektromagnetyczne

Fale elektromagnetyczne mogą być odbijane; Powierzchnia przewodnika lub dielektryka może działać jak reflektor. Ponieważ pola elektryczne i magnetyczne są posłuszne ...

Education

JoVE Core

Physics

Fizyka

Unit 1

Jednostka 1

Electromagnetic Waves

Fale elektromagnetyczne

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

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 conductor, so the electric field must be zero everywhere in the yz-plane.

The incident wave is not zero at the surface, but it induces oscillating currents on the conductor. These currents create an additional electric field. The net electric field is the vector sum of the incident and induced fields, and it is zero everywhere inside and on the conductor's surface. The same surface currents also produce a reflected wave that moves away from the plane.

The total field at any point is the vector sum of the incident and reflected electric fields, and the same idea applies to the magnetic field. This superposition creates standing waves. The places where the electric or magnetic field magnitude is zero are called nodes, or nodal planes. The planes halfway between adjacent nodes have maximum amplitude and are called antinodal planes.

For these standing waves, the total electric field follows a sine function, while the total magnetic field follows a cosine function. The two fields are therefore 90° out of phase at each point. Electric field nodes line up with magnetic field antinodes, and magnetic field nodes line up with electric field antinodes. This is different from a wave traveling in one direction, where the electric and magnetic fields are in phase at a given point.

Electromagnetic Wave Reflection at Conductors

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key terms and concepts

Explore how reflected electromagnetic waves form standing patterns at conductors, with nodes, antinodes, and electric and magnetic fields out of phase.

Electromagnetic Wave Reflection at Conductors | JoVE K12

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Minnesota Academic Standards in Science

9-12

4.2.1 9P.3.2.2.1

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New Jersey Student Learning Standards for Science

High School

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Waves and Their Applications in Technologies for Information Transfer

HS-PS4-5

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9-12.P.3.7.c

Florida Department of Education

SC.912.P.10

SC.912.P.10.17

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South Carolina College and Career Ready Science Standards

P-PS4-2

P-PS4-4

Earth and Space Science (ESS)

Earth’s Place in the Universe

E-ESS1-2.

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PS.7.b

Electromagnetic Wave Reflection at Conductors

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