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If I light a torch and hold it against a wall, will the wall feel any force? If yes, what factors does the magnitude of such a force depend upon? (Area of the wall covered by the beam, intensity of light etc).

If the answer for the above question is yes, how will energy be conserved in this process? If the light is incident on a movable object (say a toy car),light would be reflected back and also some work would be done (the car would move a little).

light energy -> light energy + work ???

Will the reflected light be reduced in intensity in order to conserve energy?

Can this force be explained using wave nature of light?

P.S I am a programmer and not very good at physics. Sorry if the question sounds stupid. Thanks for any help in advance!

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  • $\begingroup$ Yes, there will be force, but it will be because of radiation pressure, not "weight". $\endgroup$ – HDE 226868 Sep 6 '15 at 20:28
  • $\begingroup$ Yes, electromagnetic waves carry energy and momentum. Light does exert a well defined pressure when it is absorbed and reflected. Energy conservation in this case is no different than in the case of the mechanics of inelastic and elastic collisions. If a ball bounces off a fixed wall in an inelastic collision it retains is kinetic energy. If the wall starts moving as a result of that collision the ball loses kinetic energy. In case of light the wavelength will change. $\endgroup$ – CuriousOne Sep 6 '15 at 20:31
  • $\begingroup$ Here is a similar question: physics.stackexchange.com/q/55964. $\endgroup$ – Ernie Sep 6 '15 at 20:35

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