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

Electromagnetic waves transport momentum while traveling through space. The corresponding momentum density is expressed in terms of the Poynting vector magnitude and the speed of light.
By substituting the volume occupied by the wave that passes through an area in a short interval of time, the momentum flow rate per unit area can be obtained.
The average rate of momentum transfer per unit area is obtained by replacing the average value of the Poynting vector with intensity.
Due to the transfer of momentum, electromagnetic waves exert pressure on the surface, known as radiation pressure.
Now, the average rate of change of momentum equals average force and force per unit area is the radiation pressure.
Thus, the radiation pressure is directly proportional to the intensity of the wave.
If the surface perfectly absorbs the electromagnetic wave, the corresponding momentum is also transferred completely to the surface.
For a perfectly reflecting surface, the momentum change will be double. Thus, the radiation pressure also doubles.&#160;

momentum and radiation pressure

An object absorbing an electromagnetic wave would experience a force in the direction of propagation of the wave. This force occurs because electromagnetic waves contain and transport momentum. The force accounts for the wave&#39;s radiation pressure exerted on the object. Maxwell&#39;s prediction was confirmed in 1903 by Nichols and Hull by precisely measuring radiation pressures with a torsion balance. The measuring instrument had mirrors suspended from a fiber kept inside a glass container. Nichols and Hull obtained a slight measurable deflection of the mirrors from shining light on one of them. From the measured deflection, they calculated the unbalanced force on the mirror and obtained an agreement with the predicted value of the force. The radiation pressure applied by an electromagnetic wave on a perfectly absorbing surface turns out to be equal to the energy density of the wave. Suppose the material is perfectly reflecting, and the electromagnetic waves are incident normal to the surface. In that case, the pressure exerted is twice as much because the direction of momentum reverses upon reflection.
Radiation pressure plays a role in explaining many observed astronomical phenomena, including the appearance of comets. When a comet approaches the Sun, it warms up, and its surface, composed of frozen gases and particles of rock and dust, evaporates. The comet&#39;s coma is the hazy area around it made up of the gases and dust. Some of the gases and dust form tails when they leave the comet. The ion tail is composed mainly of ionized gases. These ions interact electromagnetically with the solar wind, a continuous stream of charged particles emitted by the Sun. The force of the solar wind on the ionized gases is strong enough that the ion tail almost always points directly away from the Sun. The second tail is composed of dust particles. Because the dust tail is electrically neutral, it does not interact with the solar wind. However, this tail is affected by the radiation pressure produced by the light from the Sun. Although relatively small, this pressure is strong enough to cause the dust tail to be displaced from the comet&#39;s path.

An object absorbing an electromagnetic wave would experience a force in the direction of propagation of the wave. This force occurs because ...

Education

JoVE Core

Physics

Unit 1

Electromagnetic Waves

KEY TERMS AND CONCEPTS

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

electromagnetic waves

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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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Radiation Pressure in Light and Space

Radiation pressure is the push that light can exert on matter. When an electromagnetic wave is completely absorbed by a surface, its energy density is transferred as momentum to that surface. The rate of momentum transfer on a surface perpendicular to the wave gives the force, and the force per unit area is the radiation pressure. A perfectly absorbing surface receives this pressure directly from the incoming wave. If the surface is perfectly reflecting, such as a metal surface, and the light...

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key terms and concepts

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

physics

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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Louisiana Student Standards for Science

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Radiation Pressure in Light and Comets

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