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# AQA Physics PHYA5 - Thursday 18th June 2015 [Exam Discussion Thread] watch

1. (Original post by CD223)
Parallel lines never cross so light from the object would never be able to be projected onto a screen.

How do you mean "magnified and at infinity"? Where have you seen that written?

Because I'd have thought you couldn't "magnify" an object at infinity by its very definition - the light rays never cross so no magnification can take place?

If it helps to think about it like that, then I suppose you could say they are captured at infinity, but I find it easier to grasp that they just never cross so you can't capture them.

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2. (Original post by CD223)
We don't need to know about them only type 1a, which occurs in some, but not all, white dwarf stars.

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Ahh okay thanks!
3. (Original post by JaySP)
Oh I see, sorry I thought you were talking about a single converging lens.

In normal adjustment, magnification takes place due to the relative positions of the eyepiece and objective lens.

In that case, because in normal adjustment parallel rays both enter the objective and exit the eyepiece remaining parallel, there is the effect that the image is magnified, but the rays are still parallel. Meaning the image can never be captured. It is said to be at "infinity", where we have arbitrarily said these parallel rays do cross, even though in reality they don't.

Does that help at all? It's rather abstract and hard to explain

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4. (Original post by CD223)
Oh I see, sorry I thought you were talking about a single converging lens.

In normal adjustment, magnification takes place due to the relative positions of the eyepiece and objective lens.

In that case, because in normal adjustment parallel rays both enter the objective and exit the eyepiece remaining parallel, there is the effect that the image is magnified, but the rays are still parallel. Meaning the image can never be captured. It is said to be at "infinity", where we have arbitrarily said these parallel rays do cross, even though in reality they don't.

Does that help at all? It's rather abstract and hard to explain

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Okay okay I get it thank you!

One last question, whatdo the backwards dashed lines represent?
5. (Original post by JaySP)
Okay okay I get it thank you!

One last question, whatdo the backwards dashed lines represent?
They're lines that point to a virtual image - where the image "appears" to be coming from

That's why for a single converging lens ray diagram, for an object between F and the lens, we draw construction lines backwards to see where the dashed lines intersect so we can determine where the image appears to be coming from, even though like I say, they never cross in reality.

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6. Any good exercises for Astrophysics? I seriously need practice.
7. (Original post by simonli2575)
Any good exercises for Astrophysics? I seriously need practice.
Have you done all the past papers?

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8. (Original post by CD223)
Have you done all the past papers?

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No, I plan on doing those near the exams.
9. (Original post by simonli2575)
No, I plan on doing those near the exams.
Try physicsandmathstutor

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10. (Original post by CD223)
Try physicsandmathstutor

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Right, shouldn't have forgotten about that.
Just wondering though, do you know where the questions come from
http://www.physicsandmathstutor.com/...on/aqa-unit-5/
for AQA Unit 5 questions by topic?
And why are some questions from the Edexcel and OCR list that don't seem to be in AQA?
11. (Original post by simonli2575)
Right, shouldn't have forgotten about that.
Just wondering though, do you know where the questions come from
http://www.physicsandmathstutor.com/...on/aqa-unit-5/
for AQA Unit 5 questions by topic?
And why are some questions from the Edexcel and OCR list that don't seem to be in AQA?
I must say I'd never noticed that before

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12. Spec: maximising use of W and Qout in CHP schemes?

Unit 5C applies phyics
Any ideas?
13. Im confused on the stars as black bodies, do stars only give off white light? Why do they mention only visible part if the curve (a section in the curve with all the colours), what does the others look like? and why are all stars blue, white yellow orange red? Any help would be great, thanks!
14. anyone else doing applied physics as the optional unit?
15. (Original post by getback339)
Im confused on the stars as black bodies, do stars only give off white light? Why do they mention only visible part if the curve (a section in the curve with all the colours), what does the others look like? and why are all stars blue, white yellow orange red? Any help would be great, thanks!
The black body radiation means that stars emit waves across the entire spectrum, but we only see the visible light section (unless using specialised telescopes etc.) and that's usually where the peak in the spectrum is for stars. This peak is the the frequency of most emitted radiation and so it decides the colour of the star. The peak is dependent on temperature therefore the colour of the star is also dependent on temperature.

Basically whatever colour the peak frequency corresponds to will be the colour of the star. The exception is "green" stars - as green is in the middle of the spectrum, lots of light is given off to either side of the peak as well so when the peak is green you get a white star.
16. (Original post by Lau14)
The black body radiation means that stars emit waves across the entire spectrum, but we only see the visible light section (unless using specialised telescopes etc.) and that's usually where the peak in the spectrum is for stars. This peak is the the frequency of most emitted radiation and so it decides the colour of the star. The peak is dependent on temperature therefore the colour of the star is also dependent on temperature.

Basically whatever colour the peak frequency corresponds to will be the colour of the star. The exception is "green" stars - as green is in the middle of the spectrum, lots of light is given off to either side of the peak as well so when the peak is green you get a white star.
thanks! great explanation
17. (Original post by Lau14)
The black body radiation means that stars emit waves across the entire spectrum, but we only see the visible light section (unless using specialised telescopes etc.) and that's usually where the peak in the spectrum is for stars. This peak is the the frequency of most emitted radiation and so it decides the colour of the star. The peak is dependent on temperature therefore the colour of the star is also dependent on temperature.

Basically whatever colour the peak frequency corresponds to will be the colour of the star. The exception is "green" stars - as green is in the middle of the spectrum, lots of light is given off to either side of the peak as well so when the peak is green you get a white star.

Is it essentially a case of you have red, blue and white stars only?

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18. http://filestore.aqa.org.uk/subjects...1-QP-JUN13.PDF
Can someone please explain question 4biii), as our teacher didn't go through this type of question
19. (Original post by CD223)

Is it essentially a case of you have red, blue and white stars only?

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They can definitely ask us about the first bit because that's just the basics of black body radiation (Wien's law), and I'd say the second bit isn't a huge jump (our teacher talked about it a fair bit) so it could come up I expect.
Yeah, you just have the colours in the table for OBAFGKM - basically anything except green can turn up!
20. GUYS!
Just an fyi for everyone doing this exam, got some info that I thought might help everyone:
No need to thank me.
Spoiler:
Show

Oh, I'm just an AS student :P, but ya 18th of June is my birthday!

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