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# Edexcel A2 Physics Unit 5 'Physics from Creation to Collapse' watch

1. (Original post by skypistol)
im sorry im not getting you :/
Ignore me and look at what yadas is telling you.

Hehe.. sorry for confusing you.
You know that the value of binding energy is calculated from ([mass of nucleons on their own] - [mass of these nucleons in the nucleus])/[number of those nucleons].
And this happens to be the way it is on that curve.
It's all right, I seem to be getting very confused today, I think I'll go over nuclear/astrophysics one more time.

So, I'll never have to justify the curve. All I need to know is that higher binding energy per nucleon = more stability (like iron with the whole stars no longer being able to fuse thing)?
2. (Original post by kappleberry)
http://cid-5432f573d3fc3f5a.office.l...0decay%20Q.doc

How would I do Q4 please?
Spoiler:
Show
a)
Power required = 55W = ΔE/Δt
Activity = ΔN/Δt
To get number of particles, we must divide the required energy by the the energy of each particle:
Er/E1 = N ; dividing both by Δt
ΔEr/E1Δt = ΔN/Δt
55/(7.65*10-13) = 7.19*1013Bq

b)
ƛ = ln2/t½ = ln2/(1620*3.15*107 = 1.358*10-11.

c)
A = ƛN => N = A/ƛ = (7.19*1013)/(1.358*10-11) = 5.29*1024.

Do you need the rest?
3. (Original post by kappleberry)
thank you buttt...I dont get the method of part a =/
activity is rate of decay of one disintergratin per second.
power is energy per second

to find the rate of disintergration energy per second must be divided by energy of one alpha particle.

hope that helped.hard to explain..sorry
4. (Original post by unamed)
So, I'll never have to justify the curve. All I need to know is that higher binding energy per nucleon = more stability (like iron with the whole stars no longer being able to fuse thing)?
Wel.. they might ask us to predict which of Carbon or Copper would be more stable (or have higher B/A), without calculations.
And you get that from the curve.
5. So a standard candle is an object in which its luminosity can be known through seperate measurements. But what are these measurements?

A variable star is one that has its brightness vary over time due to changes in apparent or absolute luminosity?
Spoiler:
Show
a)
Power required = 55W = ΔE/Δt
Activity = ΔN/Δt
To get number of particles, we must divide the required energy by the the energy of each particle:
Er/E1 = N ; dividing both by Δt
ΔEr/E1Δt = ΔN/Δt
55/(7.65*10-13) = 7.19*1013Bq

b)
ƛ = ln2/t½ = ln2/(1620*3.15*107 = 1.358*10-11.

c)
A = ƛN => N = A/ƛ = (7.19*1013)/(1.358*10-11) = 5.29*1024.

Do you need the rest?
So another eq for A could be A=Power/Energy of each particle ?
Wel.. they might ask us to predict which of Carbon or Copper would be more stable (or have higher B/A), without calculations.
And you get that from the curve.
But they'll give me the curve, yes? Like the one you posted - with all of the little annotations (and then I can just say that whichever one has the higher energy is more stable, yes?)
http://en.wikipedia.org/wiki/Variable_star
But I think we're not required to know that.
ok i scanned through that page but still, i was answering a few questions the teacher handed out and i got to this question, two cephid variable stars have different periods, one is longer than the other, but they have the same average Intensity.. they then ask 'deduce the luminosity of star B (which is the one with the longer period'
after that they ask about the distances of the two stars from the earth..?
9. (Original post by kappleberry)
So another eq for A could be A=Power/Energy of each particle ?
yp
if your not sure what to do..look at the units..it wud guide you
10. (Original post by Kameo)
So a standard candle is an object in which its luminosity can be known through seperate measurements. But what are these measurements?

A variable star is one that has its brightness vary over time due to changes in apparent or absolute luminosity?
Don't ask... We don't need to know.

Absolute, it seems. Since they calculated it using the parallax method, according to the good old Miles Hudson textbook.
11. (Original post by skypistol)
ok i scanned through that page but still, i was answering a few questions the teacher handed out and i got to this question, two cephid variable stars have different periods, one is longer than the other, but they have the same average Intensity.. they then ask 'deduce the luminosity of star B (which is the one with the longer period'
after that they ask about the distances of the two stars from the earth..?
You could find it using the flux equation, yes?
12. (Original post by Kameo)
So a standard candle is an object in which its luminosity can be known through seperate measurements. But what are these measurements?

A variable star is one that has its brightness vary over time due to changes in apparent or absolute luminosity?

(Original post by unamed)
But they'll give me the curve, yes? Like the one you posted - with all of the little annotations (and then I can just say that whichever one has the higher energy is more stable, yes?)
I guess yeah..
Anyway we know that B/A increases rapidly till Fe-56 and then slowly decreases.

(Original post by kappleberry)
So another eq for A could be A=Power/Energy of each particle ?
As A = dN/dt, and Power = dE/dt.
Hence P/E = 1/t, and we need the value of 'how many/t'.

Sorry, want to sleep already, 2am here..
I won't be here tomorrow.

Good luck with our exams everyone!
13. (Original post by unamed)
You could find it using the flux equation, yes?
ok i think i get it now
if I is the same, and L is bigger then d we need to be bigger too rite?

I guess yeah..
Anyway we know that B/A increases rapidly till Fe-56 and then slowly decreases.

As A = dN/dt, and Power = dE/dt.
Hence P/E = 1/t, and we need the value of 'how many/t'.

Sorry, want to sleep already, 2am here..
I won't be here tomorrow.

Good luck with our exams everyone!
Makes sense anyway.

Good luck to you too! [not that you need it ]
15. (Original post by skypistol)
ok i think i get it now
if I is the same, and L is bigger then d we need to be bigger too rite?
Yes, I think that would makes sense.
16. im refreshing my memory atm, so can someone please explain the process of fission and fusion only referring to details we are required to know
17. (Original post by skypistol)
im refreshing my memory atm, so can someone please explain the process of fission and fusion only referring to details we are required to know
Fission: when a slow-moving neutron hits an atom, making it unstable, thus causing it to break up - this produces more neutrons and 'daughter' radioactive-particles. This process is the one that is used in Nuclear power stations (but then, you have to have moderators to ensure the speed of the neutrons is slow enough to be penetrated into the atoms and there are control rods, to absorb the extra particles emitted and not used in the further chain reactions). It has a lot of harmful waste products at the end of the reaction.

Fusion: Requires high temperatures. It's when two protons go towards eachother at high speeds and fuse as they overcome the electrical charge between them. They need high temperatures as it needs a lot of energy for this to occur. This is what powers the stars. A lot cleaner than fission, and, if we can find a way to control it, would be able to end all power-related problems. So far, there is no such method.

Pretty much all you need to know. [oh and the mass deficit stuff that comes into it.]

this
is quite useful.
18. Got a few questions;

Do we need to know how to prove experimentally Charles' Law (Volume is proportional to Temperature) - Because my books only tell me how to show Boyles' and the Pressure law.

Oscillations;

My book says

If there is damping, then the resonant frequency at which the amplitude is a maximum is lower than the natural frequency, and that this difference increases as the degree of damping increase. However, the maximum energy transfer, or energy resonance, always occurs at the natural frequency.

The bit in bold I don't get. Surely when there's maximum energy transfer, the amplitude is going to be at its greatest meaning it should occur at the resonant frequency, not the natural frequency (where the amplitude isn't at its maximum when there's damping).
19. help with Q16 on :

I understand the ans UNTIL theyve taken N=1 and initial N=256...i know this has something to do with ratios. but em...what?
thank you!
20. (Original post by kappleberry)
help with Q16 on :

I understand the ans UNTIL theyve taken N=1 and initial N=256...i know this has something to do with ratios. but em...what?
thank you!
Initially there were 256 carbon atoms.since 255 decayed, 1 carbon atom was left remaining.N=Noe^-(lambda*time) N is the number of atoms REMAINING, No is the number of atoms INITIALLY(when time was 0)

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