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

dragozox
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#1501
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#1501
(Original post by Agiyuki)
Well, IIRC you can only get a red giant if it's less than 3 solar masses, like our SUn over here. the red giant's core is eventually ejected as a planetary nebulae and the core is a stupidly hot and dense white dwarf.

IF however the original mass is more than 3 solar masses it turns into a SUPER red giant which is different. eventually the super red giant explodes (which is called a supernova) and the remaining core is a Neutron star, IF the mass was even larger (or denser) the neutron core collapses more and becomes a black hole (i think)
Thanks !!!
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Wing:)
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(Original post by fatart123)
MRI, evidence for BB model and maybe a tiny bit on image intensifiers? Hoping for lots of calcs and stuff like that tbh
I really hope MRI comes up. MRI didn't come up for quite a few years. Image intensifiers, what is this?
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Jackasnacks
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Praying for as much medical physics as in jan 13 haha
Electric fields magnetic fields are just nope can't be dealing with that
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fatart123
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(Original post by Wing:))
I really hope MRI comes up. MRI didn't come up for quite a few years. Image intensifiers, what is this?
Read the X-Rays chapter. They're used to improve the brightness of an X-Ray image using the PE effect, phosphor and then accelerating the resulting electrons into a screen to light it up. More detail than that it the textbook ofc.
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Jackasnacks
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What's the r^2 here? Don't think I've ever seen/learnt this..
The q was state olbers paradox and the two assumptions made on the universe
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fatart123
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(Original post by Jackasnacks)
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What's the r^2 here? Don't think I've ever seen/learnt this..
The q was state olbers paradox and the two assumptions made on the universe
SA of sphere (universe) = 4pir^2 so number of stars you can see is prop to r^2. Intensity of light from stars follows inverse square law so implying that OP is false due to inverse square law is incorrect due to the amount of stars increasing at the same rate. So OP can't be disproved this way.

I think that's correct...
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Jackasnacks
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(Original post by fatart123)
SA of sphere (universe) = 4pir^2 so number of stars you can see is prop to r^2. Intensity of light from stars follows inverse square law so implying that OP is false due to inverse square law is incorrect due to the amount of stars increasing at the same rate. So OP can't be disproved this way.

I think that's correct...
Ah that's great cheers!
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fatart123
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(Original post by Jackasnacks)
Ah that's great cheers!
Np lad
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MO2898
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(Original post by Jackasnacks)
Praying for as much medical physics as in jan 13 haha
Electric fields magnetic fields are just nope can't be dealing with that
That's probably what made the jan 2013 grade boundaries high! People acing the medical physics memory game.
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MO2898
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(Original post by dragozox)
Hello everyone!! im one of the all nighters!!
I have a question can someone explain to me what happens after red giant based on the original mass of the star, thats
the only thing i cant find a good definition or explanation of.
thanks
For M ~ 3Msun

When iron-56 has been achieved in the core fusion stops so outward pressure reduces. This causes a brief contraction of the star which causes it's temperature to increase drastically. Due to electron degeneracy pressure the star rapidly expands and the outer layers are blown outwards into surrounding space. This is a planetary nebula. Once all the material has been blown off there remains the iron core which burns white hot. This is known as a white dwarf. After some time this may cool and become a brown dwarf.

For M > 3Msun

From a red supergiant similarly to above a supernova occurs (equivalent to planetary nebula except for much more massive stars and hence much more energetic). From here, according to the mass of the core relative to the Chanresekhar Limit (read below), it may progress to become either a neutron star or black hole.

Chandresekhar Limit - the boundary between the range of masses of a white dwarf which can either cause it to become a neutron star or black hole. Similar to critical density for the universe except for stars.

Edit: fellow all nighter here! I was actually going to sleep when I read your post and thought "screw it, I'm off to save my grade"

Haha, stay sane


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WillGood
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#1511
Man i hate all exams greater than 1h30m they just take the mick. Especially this one. Its hard core thinking for 2 hours straight.

School should have chose AQA. Short (30mins) and straight to the point. No nonsense like you lose marks for saying the same thing without the overly fancy words.
As long as you get it everything cool. Content in exams is content in text books. No chinese.

Looked at the papers and they are not as bad as people say they are.
MS is actually helpful with ECF and other things.
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L'Evil Fish
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#1512
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#1512
Fasting better not cost me
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MO2898
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(Original post by WillGood)
Man i hate all exams greater than 1h30m they just take the mick. Especially this one. Its hard core thinking for 2 hours straight.

School should have chose AQA. Short (30mins) and straight to the point. No nonsense like you lose marks for saying the same thing without the overly fancy words.
As long as you get it everything cool. Content in exams is content in text books. No chinese.

Looked at the papers and they are not as bad as people say they are.
MS is actually helpful with ECF and other things.
Edexcel isn't bad either at 1hr30 and an average of 65/80 required for A* yes please.

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dragozox
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(Original post by MO2898)
For M ~ 3Msun

When iron-56 has been achieved in the core fusion stops so outward pressure reduces. This causes a brief contraction of the star which causes it's temperature to increase drastically. Due to electron degeneracy pressure the star rapidly expands and the outer layers are blown outwards into surrounding space. This is a planetary nebula. Once all the material has been blown off there remains the iron core which burns white hot. This is known as a white dwarf. After some time this may cool and become a brown dwarf.

For M > 3Msun

From a red supergiant similarly to above a supernova occurs (equivalent to planetary nebula except for much more massive stars and hence much more energetic). From here, according to the mass of the core relative to the Chanresekhar Limit (read below), it may progress to become either a neutron star or black hole.

Chandresekhar Limit - the boundary between the range of masses of a white dwarf which can either cause it to become a neutron star or black hole. Similar to critical density for the universe except for stars.

Edit: fellow all nighter here! I was actually going to sleep when I read your post and thought "screw it, I'm off to save my grade"

Haha, stay sane


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thanks!! u saved my grade aswell hahaha
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WillGood
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Can some please explain the Photo-electric Effect for the scattering and absorption of Xray Photons.

The textbook is extremely useless. Its not straight forward. Even the explaination of the compton effect was horrible. Dont explain Compt.Eff. I get Compt.Eff.
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Leechayy
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(Original post by WillGood)
Can some please explain the Photo-electric Effect for the scattering and absorption of Xray Photons.

The textbook is extremely useless. Its not straight forward. Even the explaination of the compton effect was horrible. Dont explain Compt.Eff. I get Compt.Eff.
X-ray photon hits matter, x-ray photons are absorbed and electron is ejected as a result
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Leechayy
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Okay, so it looks like from here, I'm the last man standing

Best of luck to you all, fingers crossed we get our ideal test
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Alex621
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I just had a dream that it was a really easy paper and then I woke up to realise I hadn't even sat it yet
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MO2898
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(Original post by AlexParmenter)
I just had a dream that it was a really easy paper and then I woke up to realise I hadn't even sat it yet
Haha no way! Just four hours to go now though!
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rachelc142
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I always feel ready then come on this thread like "lol nope"

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