Edexcel physics unit 5 - Physics from Creation to Collapse ~ 19th June 2014

Original post by Kaneda

guys, you know the protostar to white dwarf process and the one which turns into a black hole
when the protostar has accreted much more mass it will turn into a blue supergiant and then into a red giant but why not into a red supergiant?

As the red giant has fused to the point where it is mostly iron, so it can no longer undergo fusion causing it to stop producing energy which prevents it from expanding anymore.
I think.. that's what it basically says in my book anyway

Reply 42

Kaneda

9

Original post by Gandalfthewhite

As the red giant has fused to the point where it is mostly iron, so it can no longer undergo fusion causing it to stop producing energy which prevents it from expanding anymore.
I think.. that's what it basically says in my book anyway

makes sense this causes it to contract-high density sudden burst of energy BOOM
Iswear the apple physics book is mch more detailed but rather complicated... do you think im missing out on info when i use the red book?

Reply 43

Kaneda

9

ImageUploadedByStudent Room1402684101.810689.jpg

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Reply 44

Original post by Kaneda

makes sense this causes it to contract-high density sudden burst of energy BOOM
Iswear the apple physics book is mch more detailed but rather complicated... do you think im missing out on info when i use the red book?

Yeah my teacher says the red books aren't very useful, and that you should just do every past paper as many times as you can

Reply 45

can anyone explain why the gas laws don't work at high pressures and low temps ??

(edited 9 years ago)

Reply 46

Original post by 13142vp

can anyone explain why the gas don't work at high pressures and low temps ??

The conditions in which a real gas will behave more and more like an ideal gas is either at:
-Very high temperatures, as the molecules of the gas have so much energy that the intermolecular forces and energy lost in collisions is negligible
-Very low pressures, as the molecules of the gas rarely collide or come into close enough proximity for intermolecular forces to be significant.

(edited 9 years ago)

Reply 47

binbinbinnn

8

hey my birthday is on the 12th as well. Happy birthday

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Reply 48

Original post by Gandalfthewhite

The conditions in which a real gas will behave more and more like an ideal gas is either at:
-Very high temperatures, as the molecules of the gas have so much energy that the intermolecular forces and energy lost in collisions is negligible
-Very low pressures, as the molecules of the gas rarely collide or come into close enough proximity for intermolecular forces to be significant.

thankss
so there are intermolecular forces at low temp?

Reply 49

Original post by 13142vp

thankss
so there are intermolecular forces at low temp?

Yeah and the energy lost is significant ..I think:s

(edited 9 years ago)

Reply 50

binbinbinnn

8

Can someone explain the process from the protostar to the white dwarf??and also Do we have to know about the nebula?
Thx

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Reply 51

Original post by binbinbinnn

Can someone explain the process from the protostar to the white dwarf??and also Do we have to know about the nebula?
Thx

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Protostar - formed from a cloud of hydrogen and helium atoms attracted by gravitational forces. cloud collapses and GPE transferred to KE leading to increase in temp. So molecules collide more until nuclear fusion occurs- leads to release in energy as EM radiation.
Sun like star - stable - Gravity=radiation pressure
- fusion of H to He
- When H runs out pressure drops, core collapses.
Sun expands to a red giant
Red giant - fusion of He
- surface temp decreases due to work done on expanding
- when He runs out, undergoes big collapse gravity takes hold
Nova/nebula - some material thrown out into space
WD- star contracts to much smaller size
- heats up
- very dense
hope that helps :smile:

please someone add if I'm missing anything

Reply 52

can anyone explain what is geostationary orbit and why satellite has to be in geostationary orbit ?

Thankss

Reply 53

MO2898

OP

7

Original post by 13142vp

can anyone explain what is geostationary orbit and why satellite has to be in geostationary orbit ?

Thankss

geostationary orbit is when a satellite remains above ONE FIXED POINT on earth...
should ideally be in a fixed point for ease of distance calculations. Also, if it was above the other side of the earth, the signal would not be able to curve around the atmosphere. Lastly, if it was moving the outgoing signal would miss it. think about it, if your computer was constantly moving about all the time how would you get to it?

Reply 54

Original post by MO2898

geostationary orbit is when a satellite remains above ONE FIXED POINT on earth...
should ideally be in a fixed point for ease of distance calculations. Also, if it was above the other side of the earth, the signal would not be able to curve around the atmosphere. Lastly, if it was moving the outgoing signal would miss it. think about it, if your computer was constantly moving about all the time how would you get to it?

ohh kk thannkss I think i got it now

Reply 55

MO2898

OP

7

Original post by 13142vp

ohh kk thannkss I think i got it now

Need I add, T for GS satellite=T for earth = 24 hours

Reply 56

nparbhoo

After reading through some examiner reports i've came up with a list of a few things to remember as well as key definitions which seem to be universal for all markschemes:

-When a question arises about radiation and its penetration, always mention what it can be stopped by and be precise ex- when talking about alpha radiation state that it can be stopped by a few mm of air.

-When asked to define the word spontaneous: "Decay cannot be influenced by external factors"

-Internal Energy: Sum of molecular potential and kinetic energies.

-Majority of the gas laws question where it says state an assumption you've made its usually "That the gas acts as an ideal gas"

-SHM: Resultant force is proportional to its displacement in the opposite direction (Or towards equilibrium position) *Depends on context.

-When speaking of resonance always state which object energy is being transferred from and to and that there is a large increase in amplitude.

-When speaking of damping its vibrations are either absorbed OR dissipated into the surroundings *Depends on context, therefore Amplitude decreases Exponentially over time.

-When speaking of how to reduce resonance when it is undesirable in a situation ex- a bridge
1.Add more damping (Shock absorbers which introduce friction and dissipate energy as heat to surroundings)
2.Change the natural frequency by making it more stiffer.

-Etot = 1/2kA^2
-Ke Max when displacement 0
-Pe Max when displacement is Max

Standard candles: Astronomical objects of known luminosity.

When mentioning radiant flux in a question: State that it is measured from earth.

-Gravitational forces and electrostatic forces both obey an inverse square law.

-Age of universe is given by 1/Ho

-Redshift: Fractional increase of light received on earth due to a recession of the source from the observer.

-When speaking about fusion and the reason for high temperatures and densities:
High Temp: Needed to overcome strong electrostatic repulsion forces
High Densities: Needed to ensure a sufficient collision rate.

And finally an explanation of the of the sun if it follows the path Main S->Red G-> White D

1. In the main sequence
-Undergoes Hydrogen fusion
-When hydrogen burns to helium core collapses under gravity.

2. Red Giant
-Sun expands to become a red giant
-Core becomes hot enough to undergo helium fusion
-When helium runs out core collapses under gravity

3.White D
-Outer layers of sun ejected into space.
-Star shrinks to become white giant
(As the core does not become hot enough for further fusion to occur)

**Hr diagram Temperature scale is reversed and its exponential.

(edited 9 years ago)

Reply 57

janine803

thanks nparbhoo for posting that for all of us! :smile:

btw, whenever we talk about fusion/fission, is it

fusion: 2 small nuclei make 1 large nuclEUS

fission: 1 large nucleus splits into 2 smaller nucleI?

i mean...what's the difference between nucles and nuclei, when do we use one and not the other??

I just did the June 2013 unit 5 for GCE and the Jan 2014 for IAL and got 70+ for both of the papers. (no wonder A* boundary for jan 2014 was 67) I don't know why they're so ridiculously easy..maybe that means the upcoming one will be hard! :frown:

Reply 58

nparbhoo