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

Ricordate le onde stazionarie formate in una corda stretta. 
Le onde stazionarie sono la combinazione di due onde che si muovono nella direzione opposta ma hanno la stessa ampiezza e frequenza.
Considera un foglio conduttore perfetto posizionato nel piano y-z. Un'onda elettromagnetica polarizzata linearmente colpisce il foglio, mentre viaggia nella direzione x negativa.
L'onda incidente induce la corrente sulla superficie del conduttore, provocando ulteriori campi elettrici, producendo un'onda riflessa con la stessa frequenza e ampiezza dell'onda incidente.
La sovrapposizione di queste due onde genera l'onda stazionaria. Semplificando queste espressioni si forniscono i punti sull'onda in cui le magnitudini del campo elettrico e del campo magnetico sono nulle. Questi sono chiamati nodi o piani nodali.
Un antinodo è un punto in cui l'ampiezza va dal massimo spostamento positivo al massimo spostamento negativo.
I nodi del campo elettrico coincidono con gli antinodi dei campi magnetici, e viceversa. Quindi, sono sfasati di 90 gradi in ogni punto.

<ol>
	<li>Young, H.D. e Freedman, R.A. (2012). Fisica universitaria con fisica moderna. San Francisco, CA: Pearson. Sezione 32.5; pagine 1069-1070.</li>
</ol>

onde elettromagnetiche stazionarie

Le onde elettromagnetiche possono essere riflesse; la superficie di un conduttore o di un dielettrico può agire come riflettore. Poiché i campi elettrici e magnetici obbediscono al principio di sovrapposizione, lo fanno anche le onde elettromagnetiche. La sovrapposizione di un'onda incidente e un'onda elettromagnetica riflessa produce un'onda stazionaria analogamente alle onde stazionarie create su una corda tesa.

Supponiamo che un foglio di un conduttore perfetto sia posto nel piano yz, e un'onda elettromagnetica polarizzata linearmente che viaggia nella direzione negativa dell'x lo colpisca. Poiché il campo elettrico non può avere una componente parallela alla superficie di un conduttore perfetto, il campo elettrico deve essere zero ovunque nel piano yz. Il campo elettrico dell'onda elettromagnetica incidente non è zero in tutti i momenti nel piano yz, ma questa onda incidente induce correnti oscillanti sulla superficie del conduttore, dando origine a un campo elettrico aggiuntivo. Il campo elettrico netto, che è la somma vettoriale di questo campo e il campo incidente, è zero ovunque all'interno e sulla superficie del conduttore. Le correnti indotte sulla superficie del conduttore producono anche un'onda riflessa che si propaga dal piano. Il principio di sovrapposizione afferma che il campo totale in qualsiasi punto è la somma vettoriale dei campi elettrici delle onde incidenti e riflessa, simile al campo magnetico. La sovrapposizione di onde incidenti e riflessa genera onde stazionarie.

<img alt="Equation1" src="/files/ftp_upload/13829/13829_Equation_1.png" style="text-align: center; height: 24px;" />

<img alt="Equation2" src="/files/ftp_upload/13829/13829_Equation_2.png" style="text-align: center; height: 22px;" />

Semplificando queste espressioni si ottengono i punti sulla superficie d'onda in cui le magnitudini del campo elettrico e magnetico sono zero. Questi sono chiamati nodi o piani nodali. A metà strada tra due piani nodali adiacenti si trovano i piani di ampiezza massima; questi sono i piani di antinodo.

Il campo elettrico totale è una funzione seno, e il campo magnetico totale è una funzione coseno. Pertanto, le variazioni sinusoidali dei due campi sono sfasate l'una rispetto all'altra in ogni punto. I nodi del campo elettrico coincidono con gli antinodi dei campi magnetici e viceversa. Di conseguenza, sono sfasati di 90° in ogni punto. Questo è in contrasto con un'onda che si propaga in una direzione, per la quale le variazioni sinusoidali dei campi elettrici e magnetici sono in fase in un punto specifico.

Onde Elettromagnetiche Stazionarie

Le onde elettromagnetiche possono essere riflesse; La superficie di un conduttore o di un dielettrico può fungere da riflettore. Poiché i campi elettrici e magnetici obbediscono ...

Education

Didattica

JoVE Core

Physics

Fisica

Unit 1

Unità 1

Electromagnetic Waves

Onde elettromagnetiche

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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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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

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4.2.1 9P.3.2.2.1

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P-PS4-2

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PS.7.b

Electromagnetic Wave Reflection at Conductors

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