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

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

(edited 8 years ago)

Reply 964

maattwileman

3

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

Reply 965

Original post by chem@uni

Anyone have good videos on this topic?

YouTube channel "LSCphysics" they have G485 lectures :-)

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Reply 966

Elcor

14

What's the definition of binding energy according to a mark scheme?

Reply 967

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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Reply 968

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?

Reply 969

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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Reply 970

The Room Student

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. :smile:

Reply 971

emparker1

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.

Reply 972

nothepreacher

18

Does anyone have the specimen paper for this exam? specimen or specification?

Found it on the OCR website. Don't worry. :smile:

(edited 8 years ago)

Reply 973

Jim997

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?

Reply 974

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. :smile:

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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Reply 975

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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Reply 976

Makashima

16

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

Reply 977

Elcor

14

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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Reply 978

jcwh97

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.

Reply 979

jcwh97