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

Elcor
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#981
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#981
I don't like the spec's open universe - I swear it should have an increasing gradient over time? It just looks like a flat universe which takes longer to approach its finite size(?).
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rachelc142
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#982
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(Original post by Elcor)
I don't like the spec's open universe - I swear it should have an increasing gradient over time? It just looks like a flat universe which takes longer to approach its finite size(?).
yes !!! me and my teacher had this discussion. its an awful graph.

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gothmog827
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#983
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(Original post by rachelc142)
yes !!! me and my teacher had this discussion. its an awful graph.

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I think maybe it's like a rootx graph, which doesn't actually tend towards a limit but has forever decreasing gradient... just a guess though
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Jigardubal
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#984
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(Original post by Elcor)
Can someone explain how the temperature of the Universe and the cosmic background radiation are linked?
After the Big Bang, fusion occurred which meant that helium was formed and in the process, gamma rays were released, over time due to the cooling of the universe, the wavelength of the gamma rays increased, and hence gamma rays became microwaves, which are present at this moment in time. Hope this helps
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kate8
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#985
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Hi, can someone please explain binding energy and how it links to E=mc2. Don't really understand it at all!
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L'Evil Fish
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#986
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#986
(Original post by Elcor)
I don't like the spec's open universe - I swear it should have an increasing gradient over time? It just looks like a flat universe which takes longer to approach its finite size(?).
Btw binding energy is the

*minimum* amount of energy to separate all the nucleons in a nucleus

I am in bed rn, going to have breakfast, make a cuppa, and do June 13 with some music, this is the type of revision I enjoy
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Engineering Lad
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#987
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#987
What does it mean when mark schemes refer to a 'Z value' in medical imaging? Z is used for acoustic impedance in ultrasound, so it doesn't make any sense. Unless it's the proton number?
Can anyone clarify?


Edit: I've realised it is the proton/atomic number.
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Elcor
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#988
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#988
(Original post by L'Evil Fish)
Btw binding energy is the

*minimum* amount of energy to separate all the nucleons in a nucleus

I am in bed rn, going to have breakfast, make a cuppa, and do June 13 with some music, this is the type of revision I enjoy
Thanks

I'm going into school for some final classes

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Oraeng
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#989
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(Original post by kate8)
Hi, can someone please explain binding energy and how it links to E=mc2. Don't really understand it at all!
Binding energy is the minimum amount of energy required to separate all the individual nucleons in a nucleus.
So for example if it were possible to separate all of the individual nucleons in a uranium-235 nucleus, there would be a difference between the mass of the nucleus itself and the sum of the masses of the individual nucleons after they were separated. This mass difference is called the 'mass defect'. The nucleus has a binding energy, so energy must be supplied in order to free the nucleons from the nucleus.
The binding energy is equal to the mass defect x c^2.
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Oraeng
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#990
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#990
(Original post by Engineering Lad)
What does it mean when mark schemes refer to a 'Z value' in medical imaging? Z is used for acoustic impedance in ultrasound, so it doesn't make any sense. Unless it's the proton number?
Can anyone clarify?
A Z value is the specific acoustic impedance for a boundary between two specific materials. For example the acoustic impedance of the boundary between muscle and fat is different to the acoustic impedance of the boundary between muscle and bone.

Is this what you're asking? Could you provide an example of where in the mark scheme it has confused you?
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kate8
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#991
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(Original post by Oraeng)
Binding energy is the minimum amount of energy required to separate all the individual nucleons in a nucleus.
So for example if it were possible to separate all of the individual nucleons in a uranium-235 nucleus, there would be a difference between the mass of the nucleus itself and the sum of the masses of the individual nucleons after they were separated. This mass difference is called the 'mass defect'. The nucleus has a binding energy, so energy must be supplied in order to free the nucleons from the nucleus.
The binding energy is equal to the mass defect x c^2.
So the energy you put into pulling a nucleus apart is converted into mass?
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Engineering Lad
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#992
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(Original post by Oraeng)
A Z value is the specific acoustic impedance for a boundary between two specific materials. For example the acoustic impedance of the boundary between muscle and fat is different to the acoustic impedance of the boundary between muscle and bone.

Is this what you're asking? Could you provide an example of where in the mark scheme it has confused you?
It was on the topic of contrast media, which I realise now are elements with a high atomic number (Z value).
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L'Evil Fish
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#993
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#993
(Original post by kate8)
So the energy you put into pulling a nucleus apart is converted into mass?
Yeah basically once separated
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Oraeng
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#994
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(Original post by kate8)
So the energy you put into pulling a nucleus apart is converted into mass?
Rather the mass lost in separating the nucleons is converted into energy as there is a decrease in mass.
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gothmog827
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#995
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(Original post by Engineering Lad)
It was on the topic of contrast media, which I realise now are elements with a high atomic number (Z value).
never even thought about this before, always just wrote had a high z value thinking it was referring to acoustic impedance
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kate8
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#996
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#996
(Original post by Oraeng)
Rather the mass lost in separating the nucleons is converted into energy as there is a decrease in mass.
But the mass of separate nucleons is greater than the mass of combined nucleons?
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Engineering Lad
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#997
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(Original post by gothmog827)
never even thought about this before, always just wrote had a high z value thinking it was referring to acoustic impedance
If you think about it, it wouldn't make any sense for it to be acoustic impedance, since it has the unit of pascal second per cubic metre, which wouldn't make an awful lot of sense with X-rays. Whereas if Z refers to the atomic number, it makes sense, since a high Z value would indicate the atoms of the medium have many electrons with which X-rays interact with, making a medium of high Z value more absorbing.
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[email protected]
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#998
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#998
List all the forces acting on the nucleons and explain them? (6 marker)

Anyone help!!!
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actanide
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#999
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#999
(Original post by [email protected])
List all the forces acting on the nucleons and explain them? (6 marker)

Anyone help!!!
you have gravitational, because nucleons have mass. This force is pretty much negligble.

you have electrostatic that repulses positive protons because theyre positive.

and then you have the strong nuclear force which has a very short range. It holds the nucleons together and at the same time it prevents them from being squashed
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actanide
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#1000
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#1000
June 2014 question 1bii) could someone draw how the graph is supposed to look like? v confused
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