How will the force of Light change with absorbtion/reflection?

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Discussion Overview

The discussion revolves around how the force exerted by light on an object varies depending on whether the light is absorbed or reflected. Participants explore concepts related to momentum, energy transfer, and the implications of different material properties on the interaction with light.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about the relationship between the force of light and its absorption or reflection, referencing the equation W = Fv.
  • Another participant mentions conservation of momentum as a relevant principle in this context.
  • A participant explains that for black materials, which absorb all frequencies of light, the change in momentum is equal to the momentum of the incoming photon. In contrast, for white materials that reflect light, the change in momentum is double that of the incoming photon due to the change in direction.
  • One participant introduces the concept of nonlinear optics, suggesting that at sufficiently high power levels, the index of refraction may change, potentially affecting the force of light.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the effects of absorption and reflection on the force of light, with no consensus reached on the overall implications or conclusions.

Contextual Notes

Participants do not fully explore the assumptions underlying their claims, such as the specific conditions under which the conservation of momentum applies or the thresholds for nonlinear optical effects.

AshleyTomo
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I am confused about whether or not the force that light exerts on an object (let's say that the power it has is 1 Watt) changes whether is is absorbed or reflected.

I know that W = Fv, but is there more to it than that?

Thank you for the help!
 
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conservation of momentum.
 
For black materials (assuming black is equivalent to absorbs all frequencies) the light is absorbed, which means, that if the light photon had momentum p, the change of momentum is also p. On the other side a white material would in fact not absorb the energy, but change the direction on the photons, which would imply a change in momentum of 2p. Now just remember, that F=dp/dt and you have your answer.
 
I think you are asking about nonlinear optics. For sufficiently high powered light, the index of refraction may change.
 

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