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# physics watch

1. how can plane polarization be expressed usin a tv aerial, and the tv set.
hence the tv aerial includes the reflector, and directional rods.
cheers.
2. (Original post by mathematician)
how can plane polarization be expressed usin a tv aerial, and the tv set.
hence the tv aerial includes the reflector, and directional rods.
cheers.
what do you mean by expressed?
3. an experiment be setup to show how waves r plane polarized usin a tv aerial and tv set.
the only thing i can think of is usin the directional rods of the aerial to plane polarize the microwaves then rotate the dipole ( reciever about 90 degrees and check the tv set )
but im not sure, becos the directional rods r in such a position where polarizing incoming microwaves will be difficult

Incoming wave directional rods Dipole receiver reflector Tv set
----------------> |||||||| : | []
4. Are radio waves in TV signals not polarised anyway?
5. you can rotate the aerial 90 degrees and get a weaker/stronger signal.

(Original post by hitchhiker_13)
Are radio waves in TV signals not polarised anyway?
They are polarised.
6. (Original post by elpaw)

They are polarised.

So, maybe I'm being stupid here, but can't you just rotate aerial, and you get a weak, or no, signal?
7. u cant just rotate the aerialcos how r u polarizing the waves?
8. (Original post by mathematician)
u cant just rotate the aerialcos how r u polarizing the waves?
are you using the same aerial to create AND detect the signal?
9. (Original post by mathematician)
u cant just rotate the aerialcos how r u polarizing the waves?
Do you have to polarise the waves or show that they are polarised?

(Edit: This goes back to Elpaw's question, what do you mean by expressed?)
10. either will help me understand?
11. (Original post by mathematician)
yes u are,
but hold on uve got natural unpolarized waves coming to the aerial yer?
how are they being plane polarized in the first place?

I'm not sure. Aren't they just passed through a polarising lens?
12. (Original post by mathematician)
either will help me understand?
OK, can you just go through your experiment, or tell us what you have been asked to do (i.e. if this is for an exam, tell us what they have written)
13. i think it has something to do with the directional rods acting as parrallel grilles to polarize the wave, then they are polarized, to which u can rotate the reciever 90 degrees to check if they are polarized but im not sure at all!
14. it just says OUTLINE how u can demonstrate experimentally, using the aerial and tv set, that the incoming wave was plane polarized?
15. Well, if you imagine waves like this with vertical axis polarisation ^^^^^^ (sorry it's the best i can do) approaching an upright aerial like this l

Well if you rotate the plane of polarisation, the aerial won't pick up the signal properly, because the waves won't be hitting the aerial.

So if you had horizontal axis polarisation, it would look a bit like this from above

^^^^^^^^^^^ . (aerial appears as point)

I'm sorry, I'm not explaining this very well. It would be a lot easier if you could draw diagrams.
16. (Original post by mathematician)
it just says OUTLINE how u can demonstrate experimentally, using the aerial and tv set, that the incoming wave was plane polarized?
then surely rotating the aerial about the axis parallel to the incoming wave direction will change the signal strength detected.
17. How many marks is the question worth?
I only ask, because if it's for 2 marks or something, it's unlikely to be anything complicated.
18. i c wot your saying but how are they vertical plane polarized in the first place where did they get polarized from
19. erms its on the AEA paper, erm 5 marks but it has another easy part to it
id say tht part is worth about 3 marks
20. (Original post by mathematician)
i c wot your saying but how are they vertical plane polarized in the first place where did they get polarized from
It doesnt matter how they got polarised, that is not what the question asks. they are just incoming waves. you dont know if they are polarised or not. that is what the question is asking you to determine. rotating the aerial will determine if they are polarised or not.

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