Why is it that when we change the light from un polarized to polarized

  • Context: Undergrad 
  • Thread starter Thread starter elabed haidar
  • Start date Start date
  • Tags Tags
    Change Light
Click For Summary

Discussion Overview

The discussion revolves around the transition from unpolarized light to polarized light, specifically addressing the reasons behind the reduction in intensity to half its original value and the focus on the electric field component in polarization.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why the intensity of light decreases to half when transitioning from unpolarized to polarized light, and whether polarization pertains solely to the electric field.
  • Another participant explains that polarization is defined in terms of the electric vector and describes how a polarizer selects components of the electric field vector, leading to an average power reduction to half.
  • A participant expresses confusion about the inability to measure the magnetic component of light, prompting a response that both electric and magnetic fields can be measured in different contexts.
  • One participant suggests that unpolarized light can be thought of as the incoherent sum of two polarized beams with orthogonal polarizations, which contributes to the energy reduction when polarized.
  • Another participant references a source that discusses the relationship between electric and magnetic fields, noting that the electric field is often considered due to its greater magnitude compared to the magnetic field in many scenarios.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the measurement of electric and magnetic components, and there is no consensus on the implications of these measurements or the reasons behind the intensity reduction.

Contextual Notes

Some statements rely on assumptions about the nature of light and polarization, and the discussion includes references to external sources that may not be universally accepted or verified within the thread.

elabed haidar
Messages
133
Reaction score
1
why is it that when we change the light from un polarized to polarized light the intensity goes to half its value and is the polarization only have to the electric field and why?? thank you
 
Science news on Phys.org


To avoid confusion (!?) we always define polarisation in terms of the Electric vector. There is, of course, a Magnetic field vector, too.
A Polariser selects the Component of the field vector in a particular plane. Vectors of all sorts can be resolved in the same way; think of an inclined plane which can give you a whole range of effective g values by varying the angle by 'choosing' the appropriate component.

Light from most sources behaves as many sources, each with a random angle of polarisation. What gets through a polariser will be the sum of all components of all the waves in the chosen plane. The average value will be 1/root2 so the power will be 1/2 of the original power.
 


so that's why i heard because we can measure the electric component but i didnt get why can't we measure the magnetic component
 


You can't actually measure either, easily with light but you can make an E probe or an M probe to measure RF fields.
 


Think of unpolarized light as the incoherent sum of two polarized beams, with orthogonal polarizations. When you polarize the light, you are letting through the beams with the one polarization and not the other, so you have half the energy getting through. The polarization of an electromagnetic wave is the electric field vector after the wave dependence has been factored out, different from the induced polarization of a material. The magnetic field vector is always there, but in free space it is trivially related to the electric field vector, so we ignore it.
 


thank you fluidistic very much i got it
 

Similar threads

Replies
10
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 6 ·
Replies
6
Views
14K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K