A2 Physics OCR Questions from past papers Watch

runny4
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Fot the June 2014 g485 paper on question 3cv why couldn't you say that the greatermass of helium nuclei means that they are travelling slower and hence less chanceof fusion?
Heres the paper and mark scheme:
http://www.ocr.org.uk/Images/243747-...of-physics.pdf
http://www.ocr.org.uk/Images/236085-...ysics-june.pdf

Also, on the June 2012 paper for g484. question 4cii, why couldn't you mention heat losses?
Heres the paper and mark scheme:
http://www.ocr.org.uk/Images/131309-...nian-world.pdf
http://www.ocr.org.uk/Images/135334-...world-june.pdf

Thank you for any help that you can offer
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Kyx
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(Original post by runny4)
Fot the June 2014 g485 paper on question 3cv why couldn't you say that the greatermass of helium nuclei means that they are travelling slower and hence less chanceof fusion?
Heres the paper and mark scheme:
http://www.ocr.org.uk/Images/243747-...of-physics.pdf
http://www.ocr.org.uk/Images/236085-...ysics-june.pdf

Also, on the June 2012 paper for g484. question 4cii, why couldn't you mention heat losses?
Heres the paper and mark scheme:
http://www.ocr.org.uk/Images/131309-...nian-world.pdf
http://www.ocr.org.uk/Images/135334-...world-june.pdf

Thank you for any help that you can offer
For the first one, I would say it is due to the binding energy of the nuclei...
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Kyx
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As for the heat loss, the device is designed to lose heat: it's a heater...
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Kyx
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Also for part one: is it not the speed, but the kinetic energy that determines whether they fuse? IDK, just a thought.
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The-Spartan
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For the first one i agree with Kyx;
For nuclear fusion to occur one needs to overcome the electrostatic forces between molecules
In the graph, at the same temperature the helium has less of a fusion chance than tritium as it has more electrostatic force.
The temperature do not forget is a measure of the average KE of a molecule, therefore the mass of the helium is irrelevant in this case as it has the same average KE.
This brings out kyx's answer to be correct, its not the speed that counts its the KE that determines whether they fuse.

As for part 2, the heat loss to surroundings is always certainly a weak response from my past experience from putting it down unless you explicitly say where the heat loss is to.
A stronger response to these kinds of questions is to relate to the liquid being heated, i.e the water temperature rising therefore pressure rising. (pV=nRT)
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runny4
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(Original post by The-Spartan)
For the first one i agree with Kyx;
For nuclear fusion to occur one needs to overcome the electrostatic forces between molecules
In the graph, at the same temperature the helium has less of a fusion chance than tritium as it has more electrostatic force.
The temperature do not forget is a measure of the average KE of a molecule, therefore the mass of the helium is irrelevant in this case as it has the same average KE.
This brings out kyx's answer to be correct, its not the speed that counts its the KE that determines whether they fuse.

As for part 2, the heat loss to surroundings is always certainly a weak response from my past experience from putting it down unless you explicitly say where the heat loss is to.
A stronger response to these kinds of questions is to relate to the liquid being heated, i.e the water temperature rising therefore pressure rising. (pV=nRT)
i get the heat loss point now but for the other one i though that the nuclei have to come close enough for the strong nuclear force to trigger fusion and this only possible with high speed.
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The-Spartan
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(Original post by runny4)
i get the heat loss point now but for the other one i though that the nuclei have to come close enough for the strong nuclear force to trigger fusion and this only possible with high speed.
the speed isnt really the main point in fusion, you need a high kinetic energy to overcome the electrostatic force.
The KE is usually attained by high speed as it is directly proportional to velocity squared, however in the graph they have given both the tritium and the helium have the same kinetic energy which is the point that really matters, you are right saying that the helium has less speed but this is irrelevant in the overcoming of a force compared to the kinetic energy.
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runny4
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(Original post by The-Spartan)
the speed isnt really the main point in fusion, you need a high kinetic energy to overcome the electrostatic force.
The KE is usually attained by high speed as it is directly proportional to velocity squared, however in the graph they have given both the tritium and the helium have the same kinetic energy which is the point that really matters, you are right saying that the helium has less speed but this is irrelevant in the overcoming of a force compared to the kinetic energy.
ok thank you
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runny4
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(Original post by The-Spartan)
For the first one i agree with Kyx;
For nuclear fusion to occur one needs to overcome the electrostatic forces between molecules
In the graph, at the same temperature the helium has less of a fusion chance than tritium as it has more electrostatic force.
The temperature do not forget is a measure of the average KE of a molecule, therefore the mass of the helium is irrelevant in this case as it has the same average KE.
This brings out kyx's answer to be correct, its not the speed that counts its the KE that determines whether they fuse.

As for part 2, the heat loss to surroundings is always certainly a weak response from my past experience from putting it down unless you explicitly say where the heat loss is to.
A stronger response to these kinds of questions is to relate to the liquid being heated, i.e the water temperature rising therefore pressure rising. (pV=nRT)
ive seen another exam question which is similar- 2bii- on the paper attached. i don't know why heat losses are allowed here.
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The-Spartan
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(Original post by runny4)
ive seen another exam question which is similar- 2bii- on the paper attached. i don't know why heat losses are allowed here.
In this case, heat losses are allowed as this is the most viable reason that there needs to be a power increase.

The keyword in this case is the energy transfer not being 100% efficient, whereas in the other example even though heat loss was a viable suggestion, it was less viable than the other suggestions.

In this question it seems OCR believe that heat loss is more viable than any other valid reason such as water expansion etc.

Do not forget however that this is an old paper, and therefore due to spec changes and regulation changes, heat loss has become less and less of an accepted answer (from what ive found, im only a student :P) over time.

OCR are strange in their ways. Look at the ideal gas assumptions for instance, this changes year to year in the mark scheme for no reason!
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runny4
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(Original post by The-Spartan)
In this case, heat losses are allowed as this is the most viable reason that there needs to be a power increase.

The keyword in this case is the energy transfer not being 100% efficient, whereas in the other example even though heat loss was a viable suggestion, it was less viable than the other suggestions.

In this question it seems OCR believe that heat loss is more viable than any other valid reason such as water expansion etc.

Do not forget however that this is an old paper, and therefore due to spec changes and regulation changes, heat loss has become less and less of an accepted answer (from what ive found, im only a student :P) over time.

OCR are strange in their ways. Look at the ideal gas assumptions for instance, this changes year to year in the mark scheme for no reason!
ok thank you
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