AQA Physics PHYA5 - 28th June 2016 [Exam Discussion Thread]

Could you possibly outline this for me?

I haven't been able to revise properly until tonight due to FP3 and S2 as well so I'm so far behind. Any ideas what to focus on? I'm so so screwed

Anyone doing Turning Points feel like they're ****ed? the mark schemes are soo specific

Formation:
-stars formed in gas clouds such as nebulae
-the dust particles are attracted towards eachother by gravity
-they form a clump which heats up as it gets more massive
-eventually forming a protostar
-as the core heats up, hydrogen can fuse into helium, this is when the star is a main sequence star
-the outward pressure of the large amounts of energy released by hydrogen fusion prevents the star from collapsing under its own gravity

Formation of a Red Giant
-the hydrogen in the core beings to run out. As the Hydrogen to helium core burning stops, the star expands and the outer layers (shells) cool down (this is when the star becomes red)
-the core heats up enough to allow helium to oxygen and carbon core burning.
-Hydrogen to helium shell burning occurs.
-Once the helium in the core runs out, Helium to oxygen and carbon shell burning occurs.
-In lower mass stars the core will not heat up to allow any more fusion so it contracts under its own gravity (this is eventually stopped due to electron degeneracy pressure) and into a white dwarf where it will continue to cool and fade away

-In a large star the gravity will cause it to contract more than in the above example (electron degeneracy pressure cannot prevent more contraction in this case) and will cause an explosion i.e. a supernova.
-leaving behind a black hole or neutron star


pls be on the spec I didn't memorise all of that for nothing lmao

I have no idea. I don't have a clue what special relativity is about so I'm probably going to focus on that

I agree. The mark scheme per kg is quite significant.

It is on the spec

"Stellar evolution: path of a star similar to our Sun on the Hertzsprung-Russell diagram from formation to white dwarf "

Gas cloud
- large dense gas and dust cloud at a few kelvin ( cold ) starts to collapse
- this could be due to gravity, shock waves from supernovae, ect.

protostar
- gas collapses and heats up
- gravitational energy to heat
- microwave and IR produced
- 2000-3000k

(T-Tauri phase)

Main sequence
- fusion of hydrogen to helium
- star stable
- about 90% of lifetime in this stage

subgiant - red giant
-hydrogen runs out
-core shrinks
-collapse causing temperature to increase
-fusion of heavier elements

Woah the banter is flying!

It doesn't appear to be anywhere on the spec so fingers crossed

Heycan you help me on question 1 aii) I was thinking of using theta = R/d, with R being 1 AU and d with the distance provided, but this results in an incorrect answer, isn't that what I'm supposed to do for parallax? I really don't understand why the mark scheme used s = r*theta

Question: http://prntscr.com/blswf1
Answer:http://prntscr.com/blswku

Heat pump/Refrigirators I literally don't get it

"Stellar evolution: path of a star similar to our Sun on the Hertzsprung-Russell diagram from formation to white dwarf"
that is from the spec but I've never seen it on past papers

Turning point in physics anyone????

Turning point in physics anyone????

-thermionic emission
-magnetic lens - condenses electron been towards sample
-(sample)
-objective lens - deflects and inverts scattered electrons
-(Inverted first image)
-microscopic lens- focuses on centre of first image and inverts into high resolution final image
-(final image)

-limitations
- Thickness of the sample can cause the electron beam to slow down therefore reducing de broglie wavelength and worsening resolution
- uneven thickness of sample can cause different amounts of diffraction for electron beam therefore making the distorting final image.

(I did this mainly for my own revision... but this is pretty much all you need to learn about them)

You seem pretty excited about the banter. Maybe calm yourself down a bit and you might emit a photon.