# PHYA5 ~ 20th June 2013 ~ A2 Physics Watch

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#681

(Original post by

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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**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

I think you can just say it's 3.26 lightyears.

**TeddyBasherz**)I think you can just say it's 3.26 lightyears.

And don't ask me to explain that . Though a diagram sums it up pretty nicely i think...

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#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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#683

Could anyone help me on the nuclear energy doc question 5 b i please

Thanks,

Smith

Thanks,

Smith

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#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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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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#685

(Original post by

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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**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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#686

(Original post by

Could anyone help me on the nuclear energy doc question 5 b i please

Thanks,

Smith

**smith50**)Could anyone help me on the nuclear energy doc question 5 b i please

Thanks,

Smith

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#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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#688

**smith50**)

Could anyone help me on the nuclear energy doc question 5 b i please

Thanks,

Smith

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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#689

(Original post by

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.

**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.

Smith

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#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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#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.

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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#693

(Original post by

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

**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'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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#694

The fission process is just shown as the neutron colliding with the U-235 and then splitting immediately.

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#695

(Original post by

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...

**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...

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#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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#697

(Original post by

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!

**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!

Smith

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#698

(Original post by

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.

**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.

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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#699

**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.

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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#700

(Original post by

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.

**Pinkhead**)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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