Polarized e/m wave and magnetism

In summary: I'll explain it. Basically, when two fields with different orientations (like E and B) come into contact, they can cancel each other out. This happens because the electric field is a vector and the magnetic field is a vector too. When they're perpendicular to each other, the electric and magnetic fields cancel each other out. But when they're not perpendicular, the electric field will reinforce the magnetic field. This is why B fields can't cancel E fields- because they're not perpendicular to each other.
  • #1
Pengwuino
Gold Member
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Ok i was wondering something. If you send some light through a polarizer... how does the magnetism get through? I know you never find E without its M... but if you can block light with a polarizer (the light coming at a different angle), why would the magnetic part come out with the light that actually made it through the polarizer (seeing as how hte magnetic part is perpendicular)
 
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  • #2
Why would it be absorbed in the first place...?What is the polarizer made of...?

Daniel.
 
  • #3
The polariser only blocks the electric field component.
 
  • #4
The convention that the polarization is in the directioon of E is just a convention.
It could just as well have been chosen to be the B direction, but E was chosen.
The E and B fields in a wave need each other. If one is absorbed the other must also decrease in proportion. Polarizers that work by absorption can absorb either the E or B field. Then the other field also is reduced because of the interconnection.
 
  • #5
A polarizer has to block either both the E and B fields, or neither of them.

A polarizer has electrons that are constrained so that they can oscillate back and forth only along a certain direction. If the incoming E field is aligned along that direction, it causes the electrons to oscillate. As the electrons oscillate, they radiate an electromagnetic wave that has its E field aligned in the same direction, and of course a B field perpendicular to it. The "new" wave is out of phase with the incoming one, so they cancel, both E and B.

If the incoming wave's E field is perpendicular to the allowed direction of oscillation of the electrons, the electrons don't oscillate. There are no "new" E and B fields to cancel the incoming ones, so the incoming fields go right on through.

An ordinary kitchen cooking rack made of parallel metal rods makes a good polarizer for microwaves. To let the waves through, you have to orient the rods perpendicular to the E field.
 
  • #6
Couldn't it be so that: given that, statistically speaking, one half of the photons (regardless of lambda) are spin +one and other half are spin -one and further, that the population penetrating a single polarizer is also 50:50. Now imagine that E is associated with say, +1 spin, and B is associated with -1 spin. When a second polarizer is coupled to the first, the transparency of both E and B photons pass freely through both when the grids are parallel but when the grids approach perpendicular the transparencies of both E and B are extinguished. Its just a thought. Cheers, Jim
 
  • #7
jtbell said:
A polarizer has to block either both the E and B fields, or neither of them.

A polarizer has electrons that are constrained so that they can oscillate back and forth only along a certain direction. If the incoming E field is aligned along that direction, it causes the electrons to oscillate. As the electrons oscillate, they radiate an electromagnetic wave that has its E field aligned in the same direction, and of course a B field perpendicular to it. The "new" wave is out of phase with the incoming one, so they cancel, both E and B.

If the incoming wave's E field is perpendicular to the allowed direction of oscillation of the electrons, the electrons don't oscillate. There are no "new" E and B fields to cancel the incoming ones, so the incoming fields go right on through.

An ordinary kitchen cooking rack made of parallel metal rods makes a good polarizer for microwaves. To let the waves through, you have to orient the rods perpendicular to the E field.


This is the best anwser. One could add that the magnetic field has always
the relation [itex] \vec{B}\ =\ \hat{R}\ \times \vec{E}[/itex], where [itex] \hat{R}[/itex] is the unit vector from the source of the
radiation. The magnetic field is not an extra degree of freedom.
(see also Jackson 14.13)

The magnetic field B is stil very useful as a separate field because the
effects of many sources from all directions may be can be added to a single
effective value B. The E components of multiple sources for instance may
cancel each other out, while the B components can add up.

Regards, Hans.
 
  • #8
Hans de Vries said:
...
The magnetic field B is stil very useful as a separate field because the
effects of many sources from all directions may be can be added to a single
effective value B. The E components of multiple sources for instance may
cancel each other out, while the B components can add up.
Could you explain how this happens. I'm not clear on why B fields can't cancel.

Thanks

Don
 

Related to Polarized e/m wave and magnetism

1. What is a polarized electromagnetic wave?

A polarized electromagnetic wave is a type of electromagnetic radiation that has its electric and magnetic fields oscillating in a specific direction. This means that the wave has a defined orientation in space, unlike unpolarized waves where the orientation is random.

2. How is polarization related to magnetism?

Polarization is related to magnetism through the interaction between the electric and magnetic fields of an electromagnetic wave. When a wave is polarized, its electric field causes charged particles to move in a specific direction, which in turn creates a magnetic field. This interaction between the electric and magnetic fields is the basis of electromagnetism.

3. What are some applications of polarized electromagnetic waves?

Polarized electromagnetic waves have a wide range of applications, including in telecommunications, optics, and medical imaging. They are also used in the production of LCD screens, where their orientation is manipulated to control the amount of light passing through the screen.

4. Can polarized electromagnetic waves be blocked or filtered?

Yes, polarized electromagnetic waves can be blocked or filtered by using materials that only allow waves with a specific orientation to pass through. This is how polarized sunglasses work - they block horizontally polarized light, reducing glare and improving visibility.

5. How is the polarization of electromagnetic waves detected?

The polarization of electromagnetic waves can be detected using special filters, called polarizers, which only allow waves with a specific orientation to pass through. These filters can be placed in front of a detector, such as a camera or a light sensor, to determine the polarization of a wave.

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