Radiation pressure Definition and 63 Threads

It is a standard result that in a blackbody radiation there is a pressure (at a certain frequency), given by $$P_\nu=\frac 1 3 U_\nu$$ However, I am quite confused by this result. Firstly, how do we even define pressure in radiation gas? I would think that this would be the pressure on a small...

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...

Radiation pressure that light provides is weak. The photon rocket only gives thrust on par with rockets if you are willing to exhaust way more energy than normally used for rocketry (antimatter/matter annihilation). By that time your exhaust beam will be loaded with enough photons to nuke...

I was thinking about how much propulsion you could get out of a solar sail, so I just did a rough calculation: A solar sail 100m*100m in size (10'000m²), with 20grams of weight per m², an additional 100kg for probe and other stuff, so 300kg probe weight. Using the solar constant of 1400W/m²...

Hello, Let me first describe the situation I am thinking of: suppose we consider an object in the form of a square with some thickness (e.g. a mirror). Suppose further, that the gravitational force pulling the object towards the sun and the radiation pressure due to the sunlight are in balance...

Homework Statement Homework Equations Radiation pressure i.e.R.P is the instantaneous pressure exerted by radiation on a perfectly absorbing surface perpendicular to the propagation vector of the radiation. Maxwell has shown that R.P = u , (1) where u is energy density R.P = F/A, (2) F...

How do you account for the conservation of momentum for a photon? Specifically, if you have light traveling in a medium where the refractive index is not constant. For example, a graded index multi mode fiber optic. So here is another diagram to help articulate my question. Inside this graded...

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...

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...

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. :CIf there's another problem like this on here please put a link. I didn't see any, but...

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...

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...

Homework Statement t has been proposed that a spaceship might be propelled in the solar system by radiation pressure, using a large sail made of foil. Assume that the mass of the ship + sail is 1780.4 kg, that the sail is perfectly reflecting, and that the sail is oriented perpendicular to the...

I am confused with the fact of radiation pressure on Wiki and my homework solution. They are both arguing that the pressure produced by a ray of light to be reflected with incident angle θ and intensity I is: $$\frac{2I\cos^2(\theta)}{c}$$ My thinking We know that: $$Ft=\Delta p$$ We see the...

I have seen the radiometer (mill in a bulb with differently coloured leaves) explained by thermodynamics, but also this: where little particles are propelled by laser beam. So, does light beam actually transfer or cause momentum in some way? If it does, is there any chance to make a...

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...

The energy of photon is $$E=\frac{hc}{\lambda}$$ Now if we have an isotropic point light source of power P, Number of photons $$N=\frac{P}{E} = \frac{P \lambda}{hc}$$ Hence one can find the change in momentum and hence the force exerted by a beam or light sources. But let's say we keep an...

Homework Statement Consider the electromagnetic radiation inside a kiln, with a volume of 1 m3 and a temperature of 1500 K. Calculate the radiation pressure inside the kiln. How does it compare with the air pressure? Homework Equations PV = NkT The Attempt at a Solution I got...

Homework Statement A laser beam of intensity I reflects from a flat, totally reflecting surface of area A whose normal makes an angle θ with the direction of the beam. Write an expression for the radiation pressure Pr[θ] exerted on the surface, in terms of the pressure Pr[p] that would be...

Homework Statement Radiation of intensity I is normally incident on an object that absorbs a fraction frac of it and reflects the rest back along the original path. What is the radiation pressure on the object? Homework Equations Radiation pressure Pr (force/unit area) Pra = I/c...

Hi, I am just trying to understand the basis of radiation pressure. I understand radiation pressure due to absorption, but I am having a hard time understanding the radiation pressure due to reflection. From what I understand there will be an incoming photon with momentum p = E/c. The normal...

can anyone tell me the applications of radiation pressure? i have manged to find out one application i.e in solar sails but still my instructor is demanding more applications. i have also found an abstract of an article its about Adiabatic electron thermal pressure fluctuations in tokamak...

Homework Statement The intensity of sunlight reaching the Earth is 1360 \frac{W}{m^2}. a.) Assuming all sunlight is absorbed, what is the radiation pressure force on the earth? Give your answer in Newtons. F_r= b.) Give your answer as a fraction of the suns gravitational force on the earth...

How to relate the radiation pressure to the internal energy of an object?? How to get that formula P=u/3?? http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law#Thermodynamic_derivation Thank you.

Hello, I found myself a little bit lost in those concepts. Assume there are many linearly polarized plane waves, all with equal amplitudes, all traveling along z direction, and their polarizations are uniformly distributed in xy plane. Then by superposition principle amplitude of total...

Homework Statement A spherical shell of diameter D, filled with hydrogen orbits the earth. The average intensity of solar radiation, in a plane perpendicular to the rays is 1.4kW/m^2. Calculate the total force of solar radiation pushing it off its orbit as a function of the shell's albedo...

Homework Statement I have an exam on Monday and I'm trying to get a few concepts straight before then. I have a few questions... 1) p = E/c for a photon. Is this also true for a wave? 2) Assuming complete absorption, radiation pressure is 1/c x Poynting vector. What happens when there's...

Homework Statement A motionless spacecraft powered by a “solar sail” at a distance of 1.20 AU from the sun has a perfectly reflective sheet of lightweight material that allows the spacecraft to accelerate by using the radiation pressure from the sun. If a certain sail is in the shape of...

Hi everyone ! This is my first post! How can we prove that during the reflection of an electromagnetic wave on the surface of a perfect conductor, the magnetic field \vec{b} acting on a surface element ds is worth half the total magnetic field \vec{B} using Ampere's Law. That is...

1. Homework Statement Estimate the radiation pressure due to a 100 W bulb at a distance of 8.4 cm from the center of the bulb. 2. Relevant equations Power= Work/Time W=Force(distance) Pressure = Force/Area = Poynting vector/speed of light 3. The Attempt at a Solution I found the cross...

Homework Statement A laser is focussed on an area A=0.1cm². The radiation pressure is p=10 pascal. Whats the power of the laser when 50% of the light is absorbed? Homework Equations I'm not sure, I tried it via: Poynting vector: S= \epsilon_{0}*c*E^{2} and radiation pressure...

Hi All, First off, everyone on this forum is amazing. Period. Second, I had a thought experiment the other day that was interesting and was hoping you could comment on it: The System: Imagine an infinitely long hollow cylinder in one direction, made of a metal (perhaps aluminum). At the...

Homework Statement A laser beam of power P and diameter D is directed upward at one circular face (of diameter d < D) of a perfectly reflecting cylinder. The cylinder is levitated because the upward radiation force matches the downward gravitational force. If the cylinder's density is ρ...

There is a great deal of misconception and misinformation surrounding the topic of radiation pressure in stars. I have found there to be a widespread idea that the cores of stars are held up primarily by radiation pressure, yet this is very rarely true. To see how bad the misinformation there...

Consider a spacecraft attached to a sheet of material, a "sail," that absorbs sunlight. Assume that the sail is positioned to face the Sun and that the combined mass of the spacecraft and the sail is m. How large does the area of the sail have to be to propel the spacecraft away from the...

Homework Statement Estimate the force on Earth due to the pressure of the radiation on Earth by the Sun. (At Earth's orbit, the intensity of sunlight is 1.37 kW/m^2.)Homework Equations Radiation Pressure=I/c Pressure=F/A Using SA of earth=510,072,000 km2 The Attempt at a Solution So I have...

Homework Statement I am trying to work out the force on a solar sail at 1AU due to radiation pressure from the Sun, and also the force on it due to the Sun's gravity. I know G=6.67x10^-11; the mass of the sun M_s=2x10^30 kg; the distance from the Earth to the Sun r=1.5x10^11 meters; the speed...

it's apparently well known that light can exert pressure on a surface, which could be used as a light sail or whatever they are called, to accelerate space ships. however, light is a transverse wave, so when it interacts with charged particles it will accelerate them in a direction perpendicular...

Can you tell me the role of electromagnetic radiation in cosmology today? 1. how much energy is in the form of light? 2. what is the spectrum of the majority of galactic clusters? 3. does the EM radiation affect the expansion of the universe or the creation of structure?

A vertically pulsed laser fires a 800 MW pulse of 220 ns duration at a small 8 mg pellet at rest. The pulse hits the mass squarely in the center of its bottom side. The speed of light is 3 × 108 m/s and the acceleration of gravity is 9.8 m/s2. If the radiation is completely absorbed...

If 1 kilogram of matter is converted into radiation and contained in 1 cubic meter, and the radiation reflects perfectly off the walls, is the pressure 9 X 10^16 or 3 X 10^16? Ie.- Is the pressure pc^2 or (pc^2)/3 (where p is the equivalent mass density) as given in...

The question I have is: Assume a 100 kg reflective load with 1m2 area at a distance of 1 million kilometers from the surface of the sun. If the sun’s temperature is 6000K and radius is 695,000 km, find the radiation pressure exerted on the object. Find how far the load would be from its...

What if I put a light object like a small paper boat in front of a large subwoofer and a loud sine wave was played, will that object move away from the sub woofer? Will the paper boat move away too if the above experiment was done in microgravity? The purpose of microgravity experiment is to...

I would like to understand better the concept of radiation pressure, my main confusion comes from the fact that if the Stress-energy tensor for electromagnetic radiation is traceless, that would imply the pressure components of the tensor equal zero, and yet it's obvious radiation exerts...

Hi everyone, I am not a physicist, so I've been looking at "layman's terms" type sources for the answers to these questions, but I'm afraid they've just left me with more questions. I'll frame the questions around the concept of solar sails: 1. Solar sails are reflective -- since some of...

The known Radiation Pressure equation is based on Special Relativity as I saw here: http://farside.ph.utexas.edu/teaching/em/lectures/node90.html I do not want relativistic. I want is a classical one that shows distinctivly the factor of brightness and the factor of frequency (colour) that...

If an electromagnetic radiation passes through a transparent medium (dielectric or conductor), and if the radiation creates a pressure upon that medium, that means that a part of the photons momentum will be transferred to the medium and the radiation will exit with a higher wavelength ? How...

I have a question about the e-m explanation of radiation pressure. As I understand it, when an e-m wave with low frequency strikes a material with a much higher resonance frequency, the displacement of the electron relative to the atom will be in phase with the electric field (well opposite...

Since radion pressure in proportional to energy flux and inversely proportional the speed of light, does that mean that energy received by the surface depends on the speed of the object. Since the distance of travel is proportional to speed, and force * distance = energy, the energy depends on...

Homework Statement Estimate the radiation pressure due to a 100-W bulb at a distance of 5.0 cm from the center of the bulb. Assume that light is complitely absorbed. Estimate the force exerted on your fingertip if you place it at this point. Assume area of the fingertip to be 1.5 cm2...