BR polarization quesion 10.2b in physics II book

[hellocubed]

I was wondering if anyone could help me out with this problem, which doesnt make any sense to me.

The question makes it clear (and the solution also states) that when the light with E wave parallel to the surface, it is more likely to reflect than refract.

And in order to have LESS light pass through the filter, how should you orient the polarization axis?
They say you should orient it 90 degrees, which makes it perpendicular and hence actual promotes LESS reflection and more refraction. Completely contradicting itself...

This question does not seem to make sense to me at all.

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[hellocubed]

Also, what do they mean when they say "respect to the ground?"

Cause, i mean the polarizing filter is ON the ground. So 90 degrees repect to the ground means its popping UP and OUT of the ground perpendicular to the surface?

 

[chiddler]

a lot more people would help you if you present the question.

 

[MedPR]

As irritating as it is when people ask for help, but aren't even willing to take the time to type out the question, I'm already open to this chapter so here goes.

This question is asking you how to reduce the intensity of light in the direction parallel to the ground. It tells you that the light moving parallel to the ground is more intense than the other direction of the unpolarized light. So, how do you take away the parallel light? By putting in a filter (polarizer) that doesn't allow light through. You want a filter that is perpendicular to the direction of the light. So you want a filter that is 90deg to the light, which is parallel to the ground. So a 90deg filter with respect to the ground is what you want.

 

[hellocubed]

thanks~ sorry for not posting the question. I would now, but I'm at work.


basically this:

http://imgur.com/jlD6c


Just make a wall to stop it

 

[SaCkO]

Ok i understood that we need to put a filter to block the one kind of light..
What iam not understanding is the Intensity thingy. Where is this thing discussed? they just threw in different concepts in this question talking about refraction, reflection and intensity of the light and Iam trying to link everything together to get to a conclusion and its not working

 

[MedPR]

Ok i understood that we need to put a filter to block the one kind of light..
What iam not understanding is the Intensity thingy. Where is this thing discussed? they just threw in different concepts in this question talking about refraction, reflection and intensity of the light and Iam trying to link everything together to get to a conclusion and its not working

The intensity of the light is probably irrelevent. It's just there to throw you off/tell you that you are trying to block like that is polarized horizontally. Therefore you need a vertical polarizer to cancel out glare.

 

[SaCkO]

The intensity of the light is probably irrelevent. It's just there to throw you off/tell you that you are trying to block like that is polarized horizontally. Therefore you need a vertical polarizer to cancel out glare.

Yes these type of questions are typical for passage questions (MCAT type), i don't know why they threw those in the chapter where iam supposed to understand the concepts presented. Anyways from what i have read so far the presentation of this chapter has been just awkward.

 

[MrNeuro]

so the vertical polarizer is allowing more of the horizontally polarized light THROUGH the lens right? its not reflecting it off?

and is the following statement correct

unpolarized light on a polarizer with vertical polarizer allows horizontally polarized light through...

got that from wiki somewhere on this forum people were claiming the opposite..

Since electric field components parallel to the wires are reflected, the transmitted wave has an electric field purely in the direction perpendicular to the wires, and is thus linearly polarized. Note that the polarization direction is perpendicular to the wires; the notion that waves "slip through" the gaps between the wires is incorrect.[2]

 

[MedPR]

so the vertical polarizer is allowing more of the horizontally polarized light THROUGH the lens right? its not reflecting it off?

My understanding is that the polarizer prevents light from passing through, therefore no light is passing over the mirror and t here is no glare produced. Horizontal light cannot pass through a vertical polarizer.

 

[MrNeuro]

My understanding is that the polarizer prevents light from passing through, therefore no light is passing over the mirror and t here is no glare produced. Horizontal light cannot pass through a vertical polarizer.

well according to wiki and a bunch of other reputable PHYSICS sources thats wrong....

horizontal light cannot pass through a horizontal polarizer.

Note that the polarization direction is perpendicular to the wires; the notion that waves "slip through" the gaps between the wires is incorrect

again im 99.999% SURE TBR IS WRONG on this one

 

[MedPR]

well according to wiki and a bunch of other reputable PHYSICS sources thats wrong....

horizontal light cannot pass through a horizontal polarizer.



again im 99.999% SURE TBR IS WRONG on this one

Imo, hyperphysics trumps all other sources.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html

 

[MrNeuro]

Imo, hyperphysics trumps all other sources.

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html

how about this empirical experiment

http://www.youtube.com/watch?v=Qv7Y-Er7rgc

@ around 0:30 sec to 1:30

and hyperphysics says

Light waves with electric fields parallel to these chains are strongly absorbed because of the dissipative effects of the electron motion in the chains. The direction perpendicular to the polyvinyl alcohol chains is the "pass" direction since the electrons cannot move freely to absorb energy.

which AGREES w/ the youtube video and wiki.....but not TBR

the large arrows on the side show what polarized light will get through the little arrows that appear then disappear is the orientation of the polarizer's wires....

is that enough evidence to prove TBR wrong? the answer should be either 0 or 180 then

EDIT:
OHHHHHHHHHHHH I got it the keyword here is POLARIZATION AXIS

TBRs figure is wrong though if the lines represent the wires of the polarizer but right if they represent the polarization axis...

So C is still right because you don't want to let in horizontal light (a horizontal polarization axis would allow it in this would have vertical wires in the polarizer) thus you'd use a polarizer with a vertical polarization axis which would have horizontal wires in the polarizer

CONCLUSION: TBR's FIGURE IS WRONG

 

[MedPR]

how about this empirical experiment

http://www.youtube.com/watch?v=Qv7Y-Er7rgc

@ around 0:30 sec to 1:30

and hyperphysics says



which AGREES w/ the youtube video and wiki.....but not TBR

the large arrows on the side show what polarized light will get through the little arrows that appear then disappear is the orientation of the polarizer's wires....

is that enough evidence to prove TBR wrong? the answer should be either 0 or 180 then

EDIT:
OHHHHHHHHHHHH I got it the keyword here is POLARIZATION AXIS

TBRs figure is wrong though if the lines represent the wires of the polarizer but right if they represent the polarization axis...

So C is still right because you don't want to let in horizontal light (a horizontal polarization axis would allow it in this would have vertical wires in the polarizer) thus you'd use a polarizer with a vertical polarization axis which would have horizontal wires in the polarizer

CONCLUSION: TBR's FIGURE IS WRONG

That video is saying everything that hyperphysics says and that I have been saying and learned from TBR.. Which part of the video are you thinking disproves TBR? And what figure are you talking about? There is no figure associated with this question or explanation.

Paraphrasing what TBR says, you get the following: "A vertical polarizer will block horizontally polarized light," which is 100% true.

 

[MrNeuro]

That video is saying everything that hyperphysics says and that I have been saying and learned from TBR.. Which part of the video are you thinking disproves TBR? And what figure are you talking about? There is no figure associated with this question or explanation.

Paraphrasing what TBR says, you get the following: "A vertical polarizer will block horizontally polarized light," which is 100% true.

the part that was confusing me is that when they say vertical polarizer i was assuming they were talking about the orientation of the wires in the polarizer. When they say vertical polarizer they are referring to a polarizer with a vertical polarization axis. If you look at their figure w/ the polarizer and the E waves coming out the lines in the polarizer are parallel to the e waves coming out. The figure is correct if the orientation of the lines in the polarizer represent the polarization axis which is NOT what the polarizer looks like in its physical form ( by physical form im referring to the orientation of the wires). A vertical polarization axis is achieved w/ horizontal wires in your polarizer. So i guess moral of the story is when they say vertical polarizer they're referring to the orientation of the light that moves through/out NOT the orientation of the wires in the polarizer.....which sort of makes sense in hindsight...

 

[MedPR]

the part that was confusing me is that when they say vertical polarizer i was assuming they were talking about the orientation of the wires in the polarizer. When they say vertical polarizer they are referring to a polarizer with a vertical polarization axis. If you look at their figure w/ the polarizer and the E waves coming out the lines in the polarizer are parallel to the e waves coming out. The figure is correct if the orientation of the lines in the polarizer represent the polarization axis which is NOT what the polarizer looks like in its physical form ( by physical form im referring to the orientation of the wires). A vertical polarization axis is achieved w/ horizontal wires in your polarizer. So i guess moral of the story is when they say vertical polarizer they're referring to the orientation of the light that moves through/out NOT the orientation of the wires in the polarizer.....which sort of makes sense in hindsight...

Not all polarizers use a wire grid, so that's the first thing.

Secondly, the image you are talking about doesn't say anything about the kind of light that exists after the polarizer. The E field and mag field are always going to be perpendicular to the propagation of the light ray and the E field is also going to be parallel to the direction of the polarizer regardless of whether it is horizontal polarized light or vertical polarized light. The big bold line after the polarizer is just showing the propagation direction, you don't know if the light is horizontal or vertical.

 

[MrNeuro]

Not all polarizers use a wire grid, so that's the first thing.

Secondly, the image you are talking about doesn't say anything about the kind of light that exists after the polarizer. The E field and mag field are always going to be perpendicular to the propagation of the light ray and the E field is also going to be parallel to the direction of the polarizer regardless of whether it is horizontal polarized light or vertical polarized light. The big bold line after the polarizer is just showing the propagation direction, you don't know if the light is horizontal or vertical.

when you say direction of the polarizer you're referring to the polarization axis correct? if so then i agree...

and are we to assume for the MCAT when they show us a polarizer the direction is representative of the polarization axis NOT the wires unless explicitly stated otherwise?

 

[MedPR]

when you say direction of the polarizer you're referring to the polarization axis correct? if so then i agree...

and are we to assume for the MCAT when they show us a polarizer the direction is representative of the polarization axis NOT the wires unless explicitly stated otherwise?

I'm kind of confused why you're hung up on this whole wire thing. Polarizers block light that is perpendicular to their direction. Wheels on a car are oriented vertically, but cars can only drive horizontally.. When we say a car is moving, we don't ask about which way the tires are oriented.

 

[MrNeuro]

I'm kind of confused why you're hung up on this whole wire thing. Polarizers block light that is perpendicular to their direction. Wheels on a car are oriented vertically, but cars can only drive horizontally.. When we say a car is moving, we don't ask about which way the tires are oriented.

yeah i know i fret over small details sometimes and freak myself out...thanks brah

 

[SaCkO]

yeah i know i fret over small details sometimes and freak myself out...thanks brah

Its all BR fault man.. these last 3 chapters about electricity and light are really built up wrongly.. This is my second time studying for MCAT and first time using BR. I got 11 on PS first time and iam hating how these chapters are presenting the material. I mean i know that Mcat passages tend to be confusing and misleading sometimes however why would you put confusing material in the chapter itself why not leave it for the passages after. I will finish these chapters here however iam sure i will go back to my old material (PR) and study them there to get the big picture again.