# Radiation pressure Definition and 7 Discussions

Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is absorbed, reflected, or otherwise emitted (e.g. black-body radiation) by matter on any scale (from macroscopic objects to dust particles to gas molecules). The associated force is called the radiation pressure force, or sometimes just the force of light.
The forces generated by radiation pressure are generally too small to be noticed under everyday circumstances; however, they are important in some physical processes and technologies. This particularly includes objects in outer space, where it is usually the main force acting on objects besides gravity, and where the net effect of a tiny force may have a large cumulative effect over long periods of time. For example, had the effects of the Sun's radiation pressure on the spacecraft of the Viking program been ignored, the spacecraft would have missed Mars' orbit by about 15,000 km (9,300 mi). Radiation pressure from starlight is crucial in a number of astrophysical processes as well. The significance of radiation pressure increases rapidly at extremely high temperatures and can sometimes dwarf the usual gas pressure, for instance, in stellar interiors and thermonuclear weapons. Furthermore, large lasers operating in space have been suggested as a means of propelling sail craft in beam-powered propulsion.
Radiation pressure forces are the bedrock of laser technology and the branches of science that rely heavily on lasers and other optical technologies. That includes, but is not limited to, biomicroscopy (where light is used to irradiate and observe microbes, cells, and molecules), quantum optics, and optomechanics (where light is used to probe and control objects like atoms, qubits and macroscopic quantum objects). Direct applications of the radiation pressure force in these fields are, for example, laser cooling (the subject of the 1997 Nobel Prize in Physics), quantum control of macroscopic objects and atoms (2013 Nobel Prize in Physics), interferometry (2017 Nobel Prize in Physics) and optical tweezers (2018 Nobel Prize in Physics).Radiation pressure can equally well be accounted for by considering the momentum of a classical electromagnetic field or in terms of the momenta of photons, particles of light. The interaction of electromagnetic waves or photons with matter may involve an exchange of momentum. Due to the law of conservation of momentum, any change in the total momentum of the waves or photons must involve an equal and opposite change in the momentum of the matter it interacted with (Newton's third law of motion), as is illustrated in the accompanying figure for the case of light being perfectly reflected by a surface. This transfer of momentum is the general explanation for what we term radiation pressure.

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1. ### Does radiation pressure depend on the wave phase?

Hello to all, Does radiation pressure depends on the wave phase of the electromagnetic wave hitting a surface? Or, can the radiation pressure be modeled as a sin/cos wave function, where force due to radiation pressure F = P/c would be the average over one cycle? (P = power, c = light speed...
2. ### Estimate the radiation pressure

Homework Statement a) Estimate the radiation pressure due to a 100 W bulb at a distance of .08 m from the center of the bulb. b) Estimate the force exerted on your fingertip if you place it at this point. (Assume an area of .0001 m2 for the fingertip.) Homework Equations F=PradA The Attempt...
3. ### [Solved] Force due to radiation pressure in oblique incidence

The radiation pressure for a perfect mirror is given by: P = 2 Ef/c * cos²(θ) Where Ef is the energy flux per area (Power/A), and θ is the angle of incidence (from: https://en.wikipedia.org/wiki/Radiation_pressure) Since force due to pressure is F = PA, force due to radiation pressure become...
4. ### Momentum in a Box of Light

Homework Statement Homework Equations <S>=c \epsilon E2/2 \Delta P = A \Delta t <S>/c The Attempt at a Solution My question is if we need the "box height"? This is my work which I'm assuming is wrong. :C If there's another problem like this on here please put a link. I didn't see any...
5. ### Why E/c = p ?

Hi people, I studying electromagnetic waves (intermediate) and I don't understand how the expression for linear momentum of a wave is obtained, if the wave doesn't carry any mass. In particular, I have to explain why the radiation pressure on a perfect absorber is half that on a perfect...
6. ### Derive Radiation Pressure in terms of N, V, hf

Homework Statement Compute the radiation pressure exerted by a gas of photons (according to kinetic theory). There are N photons, each with energy hf, the momentum is hf/c, and the walls are perfectly reflecting. Express the pressure in terms of N, V, and the product hf. Homework Equations...
7. ### Do parallel mirrors keep accelerating away from each other?

Lets say you have two perfectly reflective parallel mirrors in a frictionless vacuum. You fire off a beam of light between them, so that it bounces between them continuously. Do they continuously accelerate away from each other due to radiation pressure? I think the answer must be no, but I...