Name: electromagnetic modes in a microwave cavity
Uploaded: 2023-09-18T17:11:21.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Physical Science

PS.7

PS.7.a

Standing Waves in a Cavity

Los hornos de microondas utilizan ondas electromagnéticas para calentar los alimentos.
La mayoría de los alimentos contienen moléculas polares como el agua, que se mueven de un lado a otro con el campo eléctrico alterno. Al voltear, las moléculas sufren fricción con otras moléculas, como resultado, se genera calor.
La cámara de microondas actúa como una cavidad de resonancia donde se forman ondas electromagnéticas estacionarias por reflexión de la superficie metálica. Las dos superficies metálicas se colocan en planos nodales.
Por lo tanto, la distancia entre los planos debe ser un múltiplo integral de la mitad de la longitud de onda.
Las longitudes de onda que satisfacen esta condición se denominan longitudes de onda características, y las frecuencias correspondientes se denominan frecuencias características.
Cada frecuencia característica, forma de onda y patrón de nodo constituye un conjunto de modos normales.
Por ejemplo, un microondas doméstico típico funciona a 2,4 gigahercios, lo que corresponde a una longitud de onda fácilmente absorbida por las moléculas de agua.
Esta longitud de onda tiene nodos a 6,1 centímetros de distancia, lo que significa que la comida estará fría en estos puntos y calentada al máximo en los antinodos.
Por lo tanto, el plato giratorio del microondas se gira para tener una distribución de calor uniforme.

<ol>
	<li>Young, H.D. y Freedman, R.A. (2012). Física Universitaria con Física Moderna. San Francisco, CA: Pearson. Sección 32.5; Página 1071.</li>
</ol>

ondas estacionarias en una cavidad

Un horno de microondas y los láseres son ejemplos de ondas electromagnéticas estacionarias en una cavidad. Cuando se colocan dos placas de metal conductor paralelas en los planos nodales, se crea una cavidad donde se forman ondas estacionarias. La cavidad entre las dos placas es análoga a una cuerda estirada sostenida en los puntos x = 0 y x = L. Aquí, la distancia 'L' entre las dos placas debe ser un múltiplo entero de la mitad de la longitud de onda. Las longitudes de onda que satisfacen esta condición están dadas por: <img alt="Equation1" src="/files/ftp_upload/14213/14213_Equation_1.png" style="text-align: center; height: 40px;"> Las frecuencias correspondientes son: <img alt="Equation2" src="/files/ftp_upload/14213/14213_Equation_2.png" style="text-align: center; height: 40px;"> Cada frecuencia característica, forma de onda y patrón de nodos constituyen un conjunto de modos normales. La longitud de onda se puede estimar midiendo las posiciones de los nodos, y si se conoce la frecuencia, también se puede determinar la velocidad de la onda. Además de las superficies conductoras, la reflexión de las ondas electromagnéticas también puede ocurrir en una interfaz entre dos materiales aislantes con diferentes propiedades dieléctricas o magnéticas. El análogo mecánico es una unión de dos cuerdas con igual tensión pero diferente densidad de masa linear. Típicamente, una onda incidente en dicha superficie límite se transmite parcialmente al segundo material y se refleja parcialmente al primero. Por ejemplo, la luz se transmite a través de una ventana de vidrio, pero sus superficies también reflejan la luz.

Ondas estacionarias en una cavidad

Un microondas doméstico y láseres son ejemplos de ondas electromagnéticas estacionarias en una cavidad. Cuando se colocan dos placas metálicas conductoras ...

Education

Educación

JoVE Core

Physics

Física

Unit 1

Unidad 1

Electromagnetic Waves

Ondas electromagnéticas

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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, wave shape, and node pattern is a normal mode.

Node positions can be measured to estimate the wavelength. If the frequency is known, the wave speed can also be found. Electromagnetic waves can also reflect at the boundary between two insulating materials with different dielectric or magnetic properties.

This kind of boundary acts like a junction between two strings with the same tension but different linear mass density. A wave that reaches the boundary is partly transmitted into the second material and partly reflected back. Light passing through a glass window is one example, since the surfaces transmit some light and also reflect some of it.

Electromagnetic Modes in a Microwave Cavity

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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,...

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Electromagnetic Modes in a Microwave Cavity | JoVE K12

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PS.7.b

Electromagnetic Modes in a Microwave Cavity

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