Polarization of light

[UMICHPremed]

---

Members don't see this ad.

Hey everyone,

I have a quick question regarding polarization.

Unpolarized light radiates in planes, and when it is linearly polarized, only the electric field vectors parallel to the polarizing axis passes through. This means that the magnetic half of the light is completely blocked.

This means that the energy of the light is cut in half? After passing through the polarizer, is the light with only electric field vectors still considered electromagnetic radiation? Finally, why does the filter select for electric field vectors and not magnetic? Are there magnetic polarizers? By what mechanism do polarizers work?

Sorry, I have a lot of questions. Answers to any of those are welcome.

 

[phltz]

Unpolarized light is a jumble of photons with all different polarizations. Although each individual photon is polarized, taken as a whole, the light is unpolarized. Passing such light through a plane-polarizing filter can be considered to allow through only that component which has the electric field varying in the appropriate direction. The magnetic field comes through along with it. It would not be physically possible to have just an oscillating electrical field with no magnetic field.

 

[UMICHPremed]

Thanks again!

So I am still a bit confused.

The review book explicitly says that only the electric field component passes through and the magnetic component is blocked out. And it says that "Measuring the intensity of this light in a photocell would reveal that is has half the intensity of the unfiltered natural light."

 

[kentavr]

I am not a big expert in this question, but here are some thoughts.
1. Light wave is always electric and magnetic vectors perpendicular to each other and changing its amplitude.
If book says that magnetic component is blocked and electric pass through, then the book is wrong. They both are absorbed or passed through
2. The polarizer works due to that it has a structure from long rod-like crystals, which absorb electric vector in one direction and transparent in another. Given that non polarized light have random polarization, then some of it will be absorbed.
3. The magnetic vector is much smaller then electric, and I am not aware about any physical structures that can act on only on magnetic. But acting on electric vector automatically kills the magnetic too.
4. To estimate the intensity of passing light you have to assume that all polarization input are random and equally distributed. Then you have to sum up all electric Ex vectors that passing through x-directional polarizer. The intensity is a square of amplitude, so I = Integral(A*cos(phy))^2 d(phy)
where A - initial electric amplitude, and phy - angle of all possible directions of electric vector taken from 0 to 360.
5. Passing light is: Int(A*cos(Phy)^2 = 1/2 * A^2
Indeed, Int(cos^2 + sin^2) = 1 and Int(cos^2)=Int(sin^2) gives that Int(cos^2) = 1/2.
HTH.

 

[phltz]

What book do you have? That's so wrong, it's laughable.

 

[UMICHPremed]

I read it in a 2004 Kaplan comprehensive review book a friend lent me.