OCR Physics A G485 - Frontiers of Physics - 18th June 2015 Watch

Elcor
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#961
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#961
Can someone explain how the temperature of the Universe and the cosmic background radiation are linked?
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[email protected]
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#962
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#962
Anyone have good videos on this topic?
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L'Evil Fish
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#963
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#963
(Original post by Elcor)
Can someone explain how the temperature of the Universe and the cosmic background radiation are linked?
Wavelengths have associated temperatures

OCR say, gamma rays cooled down to microwaves, and their associated temperature is around 3K

So the fact the universe is 2.7K is proof that this cool down did occur as calculated
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actanide
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(Original post by SkilledNChilled)
REPOST: What actually is primordial helium? And what is a concise list and explanations of the evidence for the big bang? The book is quite vague. Thank you!
primordial helium is basically just a name given for a helium-4 that was produced during the big bang, few seconds after it was cool enough for the quarks to become baryons and fuse together to create helium nuclei
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maattwileman
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#965
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(Original post by SkilledNChilled)
REPOST: What actually is primordial helium? And what is a concise list and explanations of the evidence for the big bang? The book is quite vague. Thank you!
Pre-Morial helium is to do with all the fusion that happened at the start of the universe and that there was a huge imbalance of neutrons and protons mate
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rachelc142
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#966
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(Original post by [email protected])
Anyone have good videos on this topic?
YouTube channel "LSCphysics" they have G485 lectures :-)

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Elcor
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#967
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#967
What's the definition of binding energy according to a mark scheme?
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rachelc142
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(Original post by Elcor)
What's the definition of binding energy according to a mark scheme?
off the top of my head I believe it is something along the lines of
"the amount of energy required to separate a nucleus into its constituent parts"

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The Room Student
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#969
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#969
Okay... so, for a flat universe, does the universe:

- stop accelerating after an infinite amount of time, or
- stop expanding after an infinite amount of time?

The graphs that I've seen show the 'flat' line tends to the horizontal, meaning that the universe would eventually stop expanding altogether, but the text in my OCR textbook says that it would only stop accelerating (and hence still keep expanding, but at a constant rate, forever).

Can someone help clarify this for me?
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rachelc142
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#970
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(Original post by The Room Student)
Okay... so, for a flat universe, does the universe:

- stop accelerating after an infinite amount of time, or
- stop expanding after an infinite amount of time?

The graphs that I've seen show the 'flat' line tends to the horizontal, meaning that the universe would eventually stop expanding altogether, but the text in my OCR textbook says that it would only stop accelerating (and hence still keep expanding, but at a constant rate, forever).

Can someone help clarify this for me?
it will keep expanding towards a finite limit that it will never reach
ie expands for infinite amount of time but into finite amount of space
so it tends towards this limit but doesn't reach it

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The Room Student
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#971
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#971
(Original post by rachelc142)
it will keep expanding towards a finite limit that it will never reach
ie expands for infinite amount of time but into finite amount of space
so it tends towards this limit but doesn't reach it
Thanks! So after a (theoretical) infinite amount of time, it would stop growing, in effect...

Not that it ever actually would. But mathematically speaking. That makes good sense.
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emparker1
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#972
(Original post by The Room Student)
Okay... so, for a flat universe, does the universe:

- stop accelerating after an infinite amount of time, or
- stop expanding after an infinite amount of time?

The graphs that I've seen show the 'flat' line tends to the horizontal, meaning that the universe would eventually stop expanding altogether, but the text in my OCR textbook says that it would only stop accelerating (and hence still keep expanding, but at a constant rate, forever).

Can someone help clarify this for me?
The rate of expansion or acceleration will tend towards zero, therefore the size of the universe will expand to eventually reach a finite size when rate of expansion is 0.
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nothepreacher
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#973
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#973
Does anyone have the specimen paper for this exam? specimen or specification?

Found it on the OCR website. Don't worry.
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Jim997
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#974
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#974
(Original post by Elcor)
Can someone explain how the temperature of the Universe and the cosmic background radiation are linked?
cbr was supoosedly created at the Big Bang and it's the tempreture is the same as the temp of universe which supports big bang?
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rachelc142
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#975
(Original post by The Room Student)
Thanks! So after a (theoretical) infinite amount of time, it would stop growing, in effect...

Not that it ever actually would. But mathematically speaking. That makes good sense.
Yeah! ah I am glad :-) I can't remember where I first read that but yeah I liked that way of describing it too haha :-p

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xy0mz
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#976
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#976
Is it safe to not revise B scans and Pet scans since it came up last year? Or do they sometimes consecutively repeat things


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Makashima
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#977
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#977
(Original post by xy0mz)
Is it safe to not revise B scans and Pet scans since it came up last year? Or do they sometimes consecutively repeat things


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i dont think it will come up
so no point learning them, cos if it did come up; we can all basically copy off mark scheme answer out from last year
and gain full marks
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Elcor
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(Original post by emparker1)
The rate of expansion or acceleration will tend towards zero, therefore the size of the universe will expand to eventually reach a finite size when rate of expansion is 0.
..That's not true; if the rate of expansion decreased to 0, the Universe would still be expanding.

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jcwh97
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#979
(Original post by Makashima)
i dont think it will come up
so no point learning them, cos if it did come up; we can all basically copy off mark scheme answer out from last year
and gain full marks
There is nothing stopping them from repeating questions. It has happened before.
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jcwh97
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#980
(Original post by emparker1)
The rate of expansion or acceleration will tend towards zero, therefore the size of the universe will expand to eventually reach a finite size when rate of expansion is 0.
The rate of expansion never reaches 0 because that implies the universe will stop expanding and reach the finite limit, but the theory states the universe never reaches this limit. The rate of expansion is asymptotic.
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