AQA Physics A - PHYA5 (18/06/12) - Exam thread

Reply 580

BlackPoison94

2

Does anyone have the exam report for 2011?

Reply 581

username570910

2

Original post by BlackPoison94

Does anyone have the exam report for 2011?

I would also like this please :smile:

Reply 582

internet tough guy

13

Original post by TheRenaissanceMan

You need to know how to Derive the Kinetic Molecular Gas equation, the one where you have a particle in a Box. That's the only thing you need to derive (and you can confirm this in the spec)

Thanks

Reply 583

Amirrryy

1

thanks guys, gonna start now! and me too, i was counting on phya4. i need 95 UMS in this to meet my offer, ****ting it already. :/ good luck everybody!

Reply 584

JayI

Original post by internet tough guy

Guys, for nuclear fission, the mass of the original nucleus is smaller than the combined mass of the constituent nucleons that it splits into. Whereas for nuclear fusion, the combined mass of the constituent nucleons is less than what the mass becomes when they fuse into one nucleus.

Is that all correct? So 'Before' mass is always less than 'After' mass?

I guess it's just the idea that the mass of the nucleus is always less than the mass of the constituents...

In fission the complete nucleus is first and in fusion the complete nucleus is second...
So for fusion the mass before would be larger than the mass afterwards.
But for fission the mass before would be smaller than the mass afterwards.

I find it just helps to write down the sums of the before and after reactions separately and then just take the smaller one away from the bigger one - just in case i write a big equation and get them the wrong way round.

Reply 585

helpme12345

Anyone know which equations we actually use in medical physics? The CGP book talk about the intensity reflection coefficient but says you don't need to learn it :confused:

it's also in the nelson thornes notes but not on the formula sheet :s-smilie:

Reply 586

callmenighthawk

2

Everyone is all too quick to ask questions, but nobody will answer them! I have answered quite a few in this thread yet no response...

I do not understand relativity one bit.

We are told that from a from a stationary observer, time will dilate or length will contract if he observes something that is moving quickly.

Then this question comes along - 4.a.ii - http://store.aqa.org.uk/qual/gce/pdf...W-QP-JUN11.PDF and blows my brains !

Do we pretty much universally use length contracts and time dilates?

Reply 587

Ps3SuperSRG

13

Last day guys. Good luck with revision and hope we all do well. Off to do the few past papers that are actually online!

This was posted from The Student Room's Android App on my GT-I9100

Reply 588

FrightBright

Original post by helpme12345

Anyone know which equations we actually use in medical physics? The CGP book talk about the intensity reflection coefficient but says you don't need to learn it :confused:

it's also in the nelson thornes notes but not on the formula sheet :s-smilie:

Remember the distance between organs from an ultrasound. Is the distance between the partially reflected sound waves. Using the time base x on the oscilliscope, distance=(1/2)ct.

Also remember acoustic impedance. Z=pc where p is density.

Also you should know how to convert mass attenuation coefficient and attenuation coefficient.

Reply 589

internet tough guy

13

Original post by JayI

I guess it's just the idea that the mass of the nucleus is always less than the mass of the constituents...

In fission the complete nucleus is first and in fusion the complete nucleus is second...
So for fusion the mass before would be larger than the mass afterwards.
But for fission the mass before would be smaller than the mass afterwards.

I find it just helps to write down the sums of the before and after reactions separately and then just take the smaller one away from the bigger one - just in case i write a big equation and get them the wrong way round.

Thanks, just one more thing, how exactly do I explain why energy gets released in a fission process?

With fusion, its seems logical because as you've said, the mass after two nuclei have fused together is less than what it was before, so therefore the the portion of mass that has 'disappeared' must have been the energy released.

Whereas with fission, the mass afterwards is actually greater than what it was before. So how exactly does energy gets released?

Reply 590

callmenighthawk

2

Original post by internet tough guy

Thanks, just one more thing, how exactly do I explain why energy gets released in a fission process?

With fusion, its seems logical because as you've said, the mass after two nuclei have fused together is less than what it was before, so therefore the the portion of mass that has 'disappeared' must have been the energy released.

Whereas with fission, the mass afterwards is actually greater than what it was before. So how exactly does energy gets released?

The mass afterwards is less than the mass before. To compensate for this, energy is given out.

Reply 591

JayI

Original post by internet tough guy

Thanks, just one more thing, how exactly do I explain why energy gets released in a fission process?

With fusion, its seems logical because as you've said, the mass after two nuclei have fused together is less than what it was before, so therefore the the portion of mass that has 'disappeared' must have been the energy released.

Whereas with fission, the mass afterwards is actually greater than what it was before. So how exactly does energy gets released?

I'm not completely sure with that one.. trying to revise it now :tongue:

Reply 592

VisualKiddy

2

Original post by internet tough guy

Whereas with fission, the mass afterwards is actually greater than what it was before.

No it's not.

Original post by internet tough guy

So how exactly does energy gets released?

With fission, the binding energy per nucleon is less that the maximum because the nucleus is so large.

The nucleii have binding energy towards the right of the peak.

They then split into two smaller roughly equally sized daughter nucleii - each of whom have a greater binding energy per nucleon, as they are further left, towards the peak.

Therefore the overall binding energy will have increased.

At least, this is how I understand it to function. Why do you say mass afterwards is greater?

Reply 593

JayI

Original post by callmenighthawk

The mass afterwards is less than the mass before. To compensate for this, energy is given out.

Not is fission..isn't the mass of the nuclear fragmets larger than the original mass, but energy has been released..?

EDIT: ah wait.. you're right :tongue:

That makes things a LOT simpler.

Gotta stop using the notes my school gives me, they've been wrong a few times..

(edited 11 years ago)

Reply 594

helpme12345

Original post by FrightBright

Remember the distance between organs from an ultrasound. Is the distance between the partially reflected sound waves. Using the time base x on the oscilliscope, distance=(1/2)ct.

Also remember acoustic impedance. Z=pc where p is density.

Also you should know how to convert mass attenuation coefficient and attenuation coefficient.

Thanks

so we don't need to know a = ((Z1-Z2)/(Z1+Z2))^2 ?? :confused:

why do they even mention it... :facepalm:

are those the only things we need to know?

Reply 595

Maximus113

Astrophysics question:
Does anyone have any tips for the hertzsprung Russell diagram? Theres tons of differences between the different textbooks as to which type (dwarfs/giants mainly) goes where. Collins revision guide puts the giants and supergiants in a complete different position (in terms of absolute magnitude) to the Nelson Thornes textbook. Who should I trust?

Reply 596

FrightBright

Original post by VisualKiddy

No it's not.

With fission, the binding energy per nucleon is less that the maximum because the nucleus is so large.

The nucleii have binding energy towards the right of the peak.

They then split into two smaller roughly equally sized daughter nucleii - each of whom have a greater binding energy per nucleon, as they are further left, towards the peak.

Therefore the overall binding energy will have increased.

At least, this is how I understand it to function. Why do you say mass afterwards is greater?

E=mc^2, if there a higher binding energy per nucleon then the overall mass will be greater.

Reply 597

Voglie

Original post by VisualKiddy

No it's not.

With fission, the binding energy per nucleon is less that the maximum because the nucleus is so large.

The nucleii have binding energy towards the right of the peak.

They then split into two smaller roughly equally sized daughter nucleii - each of whom have a greater binding energy per nucleon, as they are further left, towards the peak.

Therefore the overall binding energy will have increased.

At least, this is how I understand it to function. Why do you say mass afterwards is greater?

Well yes.. But, you haven't shown understanding of why the energy is released in the first place, all you said was that energy is released because the daughter nuclei are more stable because they are at a larger MeV per nucleon, which isn't an explanation it's an observation.

In Nuclear Fission, energy is released because when the nucleus splits into 2, work must be done to overcome the strong nuclear force holding it together, and hence the daughter nuclei gain kinetic energy. Because of this, energy is released equal to the increase in binding energy (since the daughter nuclei are more tightly bound together than the initial large nucleus, hence increasing binding energy per nucleon).

In Nuclear Fusion, the 2 nuclei are combined forming a more stable (higher MeV per nucleon) nucleus. Energy is released due to the fact that the nucleons will be even more bound inside the nucleus and energy is released equal to the increase in binding energy. The 2 nuclei must overcome the electrostatic forces of repulsion between them, hence they must collide at high speed so that they can be close enough to interact with the strong nuclear force.

(edited 11 years ago)

Reply 598

FrightBright

Original post by helpme12345

Thanks

so we don't need to know a = ((Z1-Z2)/(Z1+Z2))^2 ?? :confused:

why do they even mention it... :facepalm:

are those the only things we need to know?

They mention it for understanding. That question has only come up once before and they gave you the formula with the question.

I think that is all you need to know, only starting learning this stuff last Tuesday :frown: