Why does three polarizers give 1/4 intensity instead of 1/6?

[UrbanXrisis]

I have a quick question about polarization. When I put a polarizer up an unpolarized source, say the polarizer blocks all the polarization in th y direction and so all the photons in the x direction comes out of the polarizer. Is the intesity halved?

It seems to me that the intensity should be halved, however, as described in http://hyperphysics.phy-astr.gsu.edu/HBASE/phyopt/polcross.html#c2"

why isn't the polarization of the of the three polarizers 1/6 the regular intensity instead of 1/4 as it describes in the example?

 

[RandallB]

why isn't the polarization of the of the three polarizers 1/6 the regular intensity instead of 1/4 as it describes in the example?

Follow the “Law of Malus” at the same web site.
After the light is polarized by filter 1 and then filter 2
Malus says 1/2 get though – and will be aligned with #2
Filter 3 is 45^o off from #2 so again
Malus says 1/2 get though – now aligned with #3

1/2 times 1/2 gives the 1/4 they were talking about
BUT remember they are comparing to the light coming though filter 1
NOT the original light.
Compared to the original assumed un-polarized source it would be 1/8.
Because, Yes the first filter removed 1/2 the light.

Another simple one:
Polarized glasses set their polarization H or V to block predominate glare caused by reflected off flat surfaces like water.
So what is the convention for defining polarization between Horizontal and Vertical?
Are Sunglasses polarized V to allow V light though, thus blocking H glare?
OR is glare V thus Sunglasses are polarized to H so that V is blocked?

What is the polarized direction aligned with in the EM wave, the E (Electric) or the M (Magnetic)?

A matter of convention - just what is the convention?
Maybe someone even knows how the convention was established.
Example: Ben Franklin or those of his time a generally credited with establishing the charge polarity convention that resulted in the electron being defined as “-" not “+”.