# PHYA5 ~ 20th June 2013 ~ A2 PhysicsWatch

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6 years ago
#681
(Original post by JayJay95)
Hey can anyone here define what a parsec is in a really concise and understandable way? all the definitons ive seen go right over my head

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(Original post by TeddyBasherz)
I think you can just say it's 3.26 lightyears.
It needs to be more than that. Something along the lines of "the distance from which the Earth and the Sun would appear to be separated from one another by one arc second".

And don't ask me to explain that . Though a diagram sums it up pretty nicely i think...
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6 years ago
#682
I don't think just saying 3.26 light years is okay. That'd be like saying a light year is so many kilometers. I mean, yes, it is, but that's not how or why it's defined - it's defined by the distance light would travel in a year.
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6 years ago
#683
Could anyone help me on the nuclear energy doc question 5 b i please
Thanks,
Smith
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6 years ago
#684
Anyone help with second part please

5 (b) (i) The radius of a gold-197 nucleus 197Au is 6.87 × 10–15 m.
79 17–3
Show that the density of this nucleus is about 2.4 × 10 kg m .
5 (b) (ii) Using the data from part b(i) calculate the radius of an aluminium-27 nucleus, 27Al. 13
(1 mark)
(2 marks)

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6 years ago
#685
(Original post by amujamu)
Anyone help with second part please

5 (b) (i) The radius of a gold-197 nucleus 197Au is 6.87 × 10–15 m.
79 17–3
Show that the density of this nucleus is about 2.4 × 10 kg m .
5 (b) (ii) Using the data from part b(i) calculate the radius of an aluminium-27 nucleus, 27Al. 13
(1 mark)
(2 marks)

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R^0 is a constant so you can just make them equal each other. R1/R2=(A1/A2)^1/3, you can use this equation to work out R2.

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6 years ago
#686
(Original post by smith50)
Could anyone help me on the nuclear energy doc question 5 b i please
Thanks,
Smith
You need to work out how many atoms of uranium 235 are in 30 grams(3% of 1000 grams). One you figured that out just times that by the energy released in one event.

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6 years ago
#687
are there any past exam questions on the core part for nuclear physics besides the aqa papers and the nelson thornes questions?
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6 years ago
#688
(Original post by smith50)
Could anyone help me on the nuclear energy doc question 5 b i please
Thanks,
Smith
only 3% of 1000g will be U-235 undergoing fission. Therefore 30g of U235 will undergo fission

moles x avogadros constant = number of atoms

30/235 x 6.02 x 10^23 = 7.685 x 10^22 atoms will react

in the previous question you must've found how much energy one U235 atom will release when it undergoes fission... so multiply this value of energy you found by the number of atoms we've just found.
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6 years ago
#689
(Original post by posthumus)
only 3% of 1000g will be U-235 undergoing fission. Therefore 30g of U235 will undergo fission

moles x avogadros constant = number of atoms

30/235 x 6.02 x 10^23 = 7.685 x 10^22 atoms will react

in the previous question you must've found how much energy one U235 atom will release when it undergoes fission... so multiply this value of energy you found by the number of atoms we've just found.
Smashing once again THANKYOU. How is turning points coming along if you don't mind could you explain to me the difference between t0 and t in time dilation relativity
Smith
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6 years ago
#690
Anyone think threads for the separate options would be a good idea? All of the different questions going on at once are confusing!
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6 years ago
#691
@ehtisham

So dude what would the calculation be?

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6 years ago
#692
Could any explain me, the shape of critical mass. What shape is good sphere, cube, rod shape. I looked at the previous posts but I don't understand.
Why is it good to have separate rods instead of one rod.
Is it good to have a lower critical mass or higher mass?

Is this correct: The critical condition is when one neutron successfully goes on to produce fission. The critical condition requires right amount of mass. The moderators are there to slow the neutrons to thermal speed. The control rods are used to slow down the fission if the rate of fission increases.
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6 years ago
#693
(Original post by smith50)
Smashing once again THANKYOU. How is turning points coming along if you don't mind could you explain to me the difference between t0 and t in time dilation relativity
Smith
I'm like half way through it in my little revision guide lol I've gotten up to electron diffraction & the microscopes, which I'm actually finding to be one of the hardest things to grasp so far at A level. I'm thinking about creating another Physics thread for just turning points discussions.

I've never been so short on time though :/ So as you'd imagine I haven't reached the last topic yet - relativity, so I've had to refer to my collins revision guide for your question...

"t" is the time measured by the observer in the rest frame.... t0 is the time relative to the observer/object which is moving... not too hard to remember since you have to divide t0 by the lorentz factor which takes speed into consideration.

Also keep in mind the lorentz factor is always less than 1 So if your dividing t0 by a value less 1 then.... t is going to get bigger obviously. Someone who is travelling slower than the "thing" they are observing must be in the reference frame to measure a longer time.

So yh "t" ... I would say is the time measuring from the reference frame.

I kinda find it hard to explain myself, most likely since I need to read over it.... must do that tonight! Hopefully - past papers start tomorrow

Hope that helped!
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6 years ago
#694
(Original post by cooldudeman)
So it becomes u236 and unstable then splits?

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Yeah but that's never highlighted as an actual step in the process (i.e. in the equation).
The fission process is just shown as the neutron colliding with the U-235 and then splitting immediately.
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6 years ago
#695
(Original post by kingm)
It needs to be more than that. Something along the lines of "the distance from which the Earth and the Sun would appear to be separated from one another by one arc second".

And don't ask me to explain that . Though a diagram sums it up pretty nicely i think...
Would "the distance to an object subtending 1 second of arc to the earths orbit" do the job?

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6 years ago
#696
Any predictions on what the QWC question on Unit 5D will be? I'm thinking safety features of a nuclear reactor? Or maybe even a comparison between the three types of radioactive emission?
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6 years ago
#697
(Original post by posthumus)
I'm like half way through it in my little revision guide lol I've gotten up to electron diffraction & the microscopes, which I'm actually finding to be one of the hardest things to grasp so far at A level. I'm thinking about creating another Physics thread for just turning points discussions.

I've never been so short on time though :/ So as you'd imagine I haven't reached the last topic yet - relativity, so I've had to refer to my collins revision guide for your question...

"t" is the time measured by the observer in the rest frame.... t0 is the time relative to the observer/object which is moving... not too hard to remember since you have to divide t0 by the lorentz factor which takes speed into consideration.

Also keep in mind the lorentz factor is always less than 1 So if your dividing t0 by a value less 1 then.... t is going to get bigger obviously. Someone who is travelling slower than the "thing" they are observing must be in the reference frame to measure a longer time.

So yh "t" ... I would say is the time measuring from the reference frame.

I kinda find it hard to explain myself, most likely since I need to read over it.... must do that tonight! Hopefully - past papers start tomorrow

Hope that helped!
Okay that's great
Smith
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6 years ago
#698
(Original post by sports_crazy)
Could any explain me, the shape of critical mass. What shape is good sphere, cube, rod shape. I looked at the previous posts but I don't understand.
Why is it good to have separate rods instead of one rod.
Is it good to have a lower critical mass or higher mass?

Is this correct: The critical condition is when one neutron successfully goes on to produce fission. The critical condition requires right amount of mass. The moderators are there to slow the neutrons to thermal speed. The control rods are used to slow down the fission if the rate of fission increases.
A sphere is the best shape since it has the least surface area. This means it a lower critical mass is needed because less neutrons escape.

By rods you mean control rods right? Separate rods are probably used to increase precision of control. You can place each rod at varying lengths within the reactor core to adjust the amount of fission neutrons.
You need a low critical mass because this means a greater efficiency. Less of the uranium is used for the same energy (I think).

And your second paragraph is correct.
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6 years ago
#699
(Original post by sports_crazy)
Could any explain me, the shape of critical mass. What shape is good sphere, cube, rod shape. I looked at the previous posts but I don't understand.
Why is it good to have separate rods instead of one rod.
Is it good to have a lower critical mass or higher mass?

Is this correct: The critical condition is when one neutron successfully goes on to produce fission. The critical condition requires right amount of mass. The moderators are there to slow the neutrons to thermal speed. The control rods are used to slow down the fission if the rate of fission increases.
A sphere would be used because it has the lowest surface area for mass which means that less neutrons leave it without continuing the reaction. This is what is commonly used in nuclear weapons. Cylinders however are used in most reactors as they are easier to insert into the reactor vessel and the moderator and control rods can be better fitted around them yet they still have less surface area than something like a cube.

That is correct, moderators, such as heavy water slow the nuetrons to fermal speed. Control rods however are to absorb some of the neutrons to ensure the reaction continues at a steady average rate.
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6 years ago
#700
A sphere is the best shape since it has the least surface area. This means it a lower critical mass is needed because less neutrons escape.

By rods you mean control rods right? Separate rods are probably used to increase precision of control. You can place each rod at varying lengths within the reactor core to adjust the amount of fission neutrons.
You need a low critical mass because this means a greater efficiency. Less of the uranium is used for the same energy (I think).

And your second paragraph is correct.
Thanks. I was talking about fuel rod. Why dont we use a sphere instead of fuel rods. Is it because using seperate fuel rods increases the chances of successful fission.
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