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

Elektromagnetische Wellen transportieren Impulse, während sie sich durch den Weltraum bewegen. Die entsprechende Impulsdichte wird in Form der Größe des Poynting-Vektors und der Lichtgeschwindigkeit ausgedrückt.
Durch Substitution des Volumens, das von der Welle eingenommen wird, die in einem kurzen Zeitintervall durch ein Gebiet geht, kann die Impulsflussrate pro Flächeneinheit erhalten werden.
Die durchschnittliche Rate der Impulsübertragung pro Flächeneinheit erhält man, indem man den Durchschnittswert des Poynting-Vektors durch die Intensität ersetzt.
Durch die Übertragung von Impuls üben elektromagnetische Wellen Druck auf die Oberfläche aus, den sogenannten Strahlungsdruck.
Nun ist die durchschnittliche Änderungsrate des Impulses gleich der durchschnittlichen Kraft und die Kraft pro Flächeneinheit ist der Strahlungsdruck.
Somit ist der Strahlungsdruck direkt proportional zur Intensität der Welle.
Absorbiert die Oberfläche die elektromagnetische Welle perfekt, wird auch der entsprechende Impuls vollständig auf die Oberfläche übertragen.
Für eine perfekt reflektierende Oberfläche ist die Impulsänderung doppelt so groß. Somit verdoppelt sich auch der Strahlungsdruck.

<ol>
	<li>OpenStax. (2019). Universitätsphysik Vol. 2. [Webversion]. Abgerufen von <a href="https://openstax.org/books/university-physics-volume-2/pages/16-4-momentum-and-radiation-pressure">16.4 Impuls und Strahlungsdruck - Universitätsphysik Band 2 | OpenStax</a></li>
</ol>

momentum und strahlungsdruck

Ein Objekt, das eine elektromagnetische Welle absorbiert, würde eine Kraft in Richtung der Ausbreitung der Welle erfahren. Diese Kraft tritt auf, weil elektromagnetische Wellen einen Impuls enthalten und transportieren. Die Kraft erklärt den Strahlungsdruck der Welle, der auf das Objekt ausgeübt wird. Maxwells Vorhersage wurde 1903 von Nichols und Hull bestätigt, indem sie Strahlungsdrücke mit einer Torsionswaage präzise maßen. Das Messinstrument hatte an einer Faser aufgehängte Spiegel, die in einem Glasbehälter aufbewahrt wurden. Nichols und Hull erzielten eine geringfügige messbare Ablenkung der Spiegel, als Licht auf einen von ihnen schien. Aus der gemessenen Ablenkung berechneten sie die unausgeglichene Kraft auf den Spiegel und erzielten eine Übereinstimmung mit dem vorhergesagten Wert der Kraft. Der Strahlungsdruck, den eine elektromagnetische Welle auf einer perfekt absorbierenden Oberfläche ausübt, erweist sich als gleich der Energiedichte der Welle. Angenommen, das Material ist perfekt reflektierend und die elektromagnetischen Wellen treffen senkrecht auf die Oberfläche, dann ist der ausgeübte Druck doppelt so groß, weil sich die Richtung des Momentums bei der Reflexion umkehrt.

Der Strahlungsdruck spielt bei der Erklärung vieler beobachteter astronomischer Phänomene eine Rolle, einschließlich des Erscheinungsbilds von Kometen. Wenn sich ein Komet der Sonne nähert, erwärmt er sich und seine Oberfläche, die aus gefrorenen Gasen und Partikeln aus Gestein und Staub besteht, verdampft. Die Koma des Kometen ist der neblige Bereich um ihn herum, der aus den Gasen und dem Staub besteht. Einige der Gase und der Staub bilden Schweife, wenn sie den Kometen verlassen. Der Ionen-Schweif besteht hauptsächlich aus ionisierten Gasen. Diese Ionen interagieren elektromagnetisch mit dem Sonnenwind, einem kontinuierlichen Strom geladener Teilchen, der von der Sonne ausgestoßen wird. Die Kraft des Sonnenwinds auf die ionisierten Gase ist stark genug, dass der Ionen-Schweif fast immer direkt von der Sonne wegzeigt. Der zweite Schweif besteht aus Staubpartikeln. Da der Staub-Schweif elektrisch neutral ist, interagiert er nicht mit dem Sonnenwind. Allerdings wird dieser Schweif durch den Strahlungsdruck, der durch das Licht von der Sonne erzeugt wird, beeinflusst. Dieser Druck ist zwar relativ gering, aber stark genug, um den Staubschweif von der Kometenbahn zu verdrängen.

Momentum und Strahlungsdruck

Ein Objekt, das eine elektromagnetische Welle absorbiert, würde eine Kraft in Richtung der Ausbreitung der Welle erfahren. Diese Kraft tritt auf, weil ...

Education

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JoVE Core

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Unit 1

Einheit 1

Electromagnetic Waves

Elektromagnetische Wellen

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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

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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...

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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

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3.3.9-12.L

Radiation Pressure in Light and Comets

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