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

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)

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?

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...

Ah that's great cheers!

Praying for as much medical physics as in jan 13 haha
Electric fields magnetic fields are just nope can't be dealing with that

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

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.

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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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.

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