# PHYA5 ~ 20th June 2013 ~ A2 PhysicsWatch

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6 years ago
#1621
(Original post by posthumus)
de Broglie one .... 4 marker. I thought it was pretty sneaky

did anyone convert the eV into V by multiply eV by e

then multiplying it by e again to get eV

I thought it was sneaky as hell
Do you remember the answer you got?
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6 years ago
#1622
(Original post by posthumus)
de Broglie one .... 4 marker. I thought it was pretty sneaky

did anyone convert the eV into V by multiply eV by e

then multiplying it by e again to get eV

I thought it was sneaky as hell
I only multiplied it by e once because an electron volt is voltage, so you multiply it by charge to get energy
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6 years ago
#1623
(Original post by #Bi-Winning)
You did? Didn't the question say it was known to be 0.50m and you had to show it?
Wasn't it just the inverse of the sum of the two distances they gave?
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6 years ago
#1624
(Original post by The H)
I only multiplied it by e once because an electron volt is voltage, so you multiply it by charge to get energy
Hmmm not sure

But e x V would give you energy

but they gave you eV... it looks like they've given you kinetic energy already which was so misleading

was a 4 marker, that's the one I didn't have a good feeling about
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6 years ago
#1625
by the way anyone know for astrophysics i got the resolving angle wrong for the radio wave, but for the show that were we meant to multiply the radius of the event horizon by 2?
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6 years ago
#1626
(Original post by Jam Jam24)
Yeah same i got 2.5x10-19, but i didnt write that done cos i thought it was wrong i still wrote the method out, will i get a few marks?
I got this but apparently you were supposed to say charge is quantised and can only be present in multiples of two hence the 1.6x10^-19
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6 years ago
#1627
I got 17.8 MeV for the mass difference one?
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6 years ago
#1628
(Original post by posthumus)
Hmmm not sure

But e x V would give you energy

but they gave you eV... it looks like they've given you kinetic energy already which was so misleading

was a 4 marker, that's the one I didn't have a good feeling about
That's the problem in some cases, confusion between the equation eV and the unit eV
As a unit, eV is electron volt so it must be multiplied by charge to make it J
As an equation eV is the total energy, like eV = 1/2mv^2
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6 years ago
#1629
(Original post by SpiggyTopes)
Attachment 228434

The formation of Helium gives off much more energy per nucleon than a normal fission. It's just over 7MeV per nucleon and there are 4 nucleons so that's 20-something MeV
I agree that that's around the answer for the question, but you're still missing the point fission reactions produce more energy than fusion reactions. I understand that there is a greater change in binding energy, and hence more energy released PER NUCLEON, but since there are so many more nucleons in fission, it outputs more energy. Even though the change in binding energy is only around 1Mev per nucleon, there are around 200 nucleons involved, so it's much more

http://en.wikipedia.org/wiki/Nuclear_fission#Output

says that it's 200MeV

this isn't even the question so it doesn't really matter
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6 years ago
#1630
What was the answer for mass at -50degrees.
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6 years ago
#1631
(Original post by sports_crazy)
What was the answer for mass at -50degrees.
I got around 3.9 mols which corresponded to 0.166kg - 0.17kg mass
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6 years ago
#1632
(Original post by bugsuper)
I agree that that's around the answer for the question, but you're still missing the point fission reactions produce more energy than fusion reactions. I understand that there is a greater change in binding energy, and hence more energy released PER NUCLEON, but since there are so many more nucleons in fission, it outputs more energy. Even though the change in binding energy is only around 1Mev per nucleon, there are around 200 nucleons involved, so it's much more

http://en.wikipedia.org/wiki/Nuclear_fission#Output

says that it's 200MeV

this isn't even the question so it doesn't really matter

What section is this?
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6 years ago
#1633
Core Questions

Question 1

a) Definition of atomic mass unit = 1/12th of the mass of Carbon-12 atom
b) Why do stars need a high temperature for fusion to occur?
- Fusion is when two smaller nuclei combine
- This occurs when the electrostatic force of repulsion is overcome
- Since Temperature is proportional to kinetic energy, a high temperature gives the nuclei enough energy to overcome the electrostatic force
c) Fill in the gaps : Positron emission
d) Energy released = 24.7 MeV (can't remember)

Question 2

a) How do you decrease power output?
- By lowering the control rods
- which absorb the neutrons
- and therefore lower the rate of fission reactions
b) What is the source of the nuclear waste?
- used fuel rods
- fission fragments are highly unstable (usually neutron rich)
c) Describe and explain the radiation emitted by the moderator...
- electrons in the nucleus are excited
- when the electrons de-excite, photons of discrete wavelengths are produced
- these photons have a high frequency and high energy (E=hf)
- they are therefore gamma photons

Question 3

a) Temperature change = 8.5... Degrees Celsius
b)
c) Mass of ice = 0.16kg (exact values) 0.15kg (8 degrees Celsius used)

Question 4

a) What is an ideal gas?
- a gas that obeys Boyle's Law
- i.e. pV = constant at constant temperature
b) Number of moles
- 130 moles
c) Density
- 26 kgm^-3
d) Mass of gas left in cylinder
- Can't remember

Question 5
Discuss how you can determine what radiation is produced by the source using different absorbers. Discuss the safety precautions, what you would measure and what conclusions you can make

Please add to this
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6 years ago
#1634
(Original post by bugsuper)
I agree that that's around the answer for the question, but you're still missing the point fission reactions produce more energy than fusion reactions. I understand that there is a greater change in binding energy, and hence more energy released PER NUCLEON, but since there are so many more nucleons in fission, it outputs more energy. Even though the change in binding energy is only around 1Mev per nucleon, there are around 200 nucleons involved, so it's much more

http://en.wikipedia.org/wiki/Nuclear_fission#Output

says that it's 200MeV

this isn't even the question so it doesn't really matter
fusion releases more energy than fission?
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6 years ago
#1635
(Original post by wy95)
What section is this?
the core one, but it's not relevant to the question, I was just explaining to someone why a fusion reaction wouldn't emit hundreds of MeV and it descended into an argument about which process releases more
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6 years ago
#1636
(Original post by sports_crazy)
What was the answer for mass at -50degrees.
I think I got 3 kilos or something. I'm not sure if I remember rightly though.
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6 years ago
#1637
(Original post by The H)
That's the problem in some cases, confusion between the equation eV and the unit eV
As a unit, eV is electron volt so it must be multiplied by charge to make it J
As an equation eV is the total energy, like eV = 1/2mv^2
Oh well, lets not worry too much about it now

I'm pretty sure regardless we have both got 2 marks at least

I hope grade boundaries are low - by the sounds of it here, people found it quite easy.... my class found it tough though
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6 years ago
#1638
(Original post by posthumus)
Oh well, lets not worry too much about it now

I'm pretty sure regardless we have both got 2 marks at least

I hope grade boundaries are low - by the sounds of it here, people found it quite easy.... my class found it tough though
I thought on average it was significantly easier than the others, although there were a few questions I didn't like
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6 years ago
#1639
(Original post by Acruzen)
fusion releases more energy than fission?
FISSION releases more energy than FUSION
because even though the change in binding energy for each nucleon is less there are more nucleons involved
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6 years ago
#1640
(Original post by bugsuper)
I agree that that's around the answer for the question, but you're still missing the point fission reactions produce more energy than fusion reactions. I understand that there is a greater change in binding energy, and hence more energy released PER NUCLEON, but since there are so many more nucleons in fission, it outputs more energy. Even though the change in binding energy is only around 1Mev per nucleon, there are around 200 nucleons involved, so it's much more

http://en.wikipedia.org/wiki/Nuclear_fission#Output

says that it's 200MeV

this isn't even the question so it doesn't really matter
Yes you're right, sorry. I must have misread what you said, I thought you said 24.7 seemed too high.
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