AQA Physics PHYA5 - Thursday 18th June 2015 [Exam Discussion Thread]

Reply 1960

i really dont understand what is meant by critical mass in fission reaction, can someone explain it to me pls

The critical mass is the smallest mass of fissile material in the fuel rods required to provide a sustainable chain reaction.

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Reply 1961

gcsestuff

2

Original post by coqthepoliceman

i really dont understand what is meant by critical mass in fission reaction, can someone explain it to me pls

Critical mass is- the minimum amount of mass required for a self sustaining nuclear fission reactor. This means that it has enough fissionable material in the fuel so that when a thermal neutron hit the fuel rod it has a good chance of hitting a fissionable nuclei.

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Reply 1962

MSB47

2

Original post by coqthepoliceman

i really dont understand what is meant by critical mass in fission reaction, can someone explain it to me pls

In order to maintain a reaction rate of one neutron per fission to cause another fission.

So you'll need a critical mass of fuel to maintain this... If you go below it than the nuclear reactor will cease to function you go above then it would go out of control.

Correct me if I'm wrong please :smile:

Reply 1963

Exams12343

Can someone help explain Q 2b on the june 2011 paper please?

Reply 1964

coqthepoliceman

thanks for clearing that up, just couldnt understand the wording of the book

Reply 1965

moontheloon

1

Original post by MSB47

In order to maintain a reaction rate of one neutron per fission to cause another fission.

So you'll need a critical mass of fuel to maintain this... If you go below it than the nuclear reactor will cease to function you go above then it would go out of control.

Correct me if I'm wrong please :smile:

You are correct. However, something to note, in actual fission reactors they use super critical mass (i.e. greater than the critical mass) and use control rods to limit the reaction rate by raising or lowering the control rods into the reactor.

Reply 1966

Absent Agent

21

Original post by gcsestuff

Yeah that's what I'm trying to do :smile:

I always think about the space ship and time so I know moving objects time is slower but what do you think about for the other

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So the same with others. A moving body has kinetic energy and so has a greater mass than its rest mass.
With the length it's quite tricky thinking about it. Of course a moving body shrinks in length but also the distance the moving body travels shrinks because as the time in the moving frame of reference slows down this means that the distance the moving frame travels has to shrink so that the stationary observer will see that the moving frame travels the same distance in the same time, if that makes sense but I'm not really sure about the length contraction of the moving frame itself

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Reply 1967

CD223

OP

10

Original post by _Caz_

X

Can I ask how it got the value for (a) in your Astro telescope CGP question?

I got this, which I know I wrong according to the mark scheme you posted, but if it's a single 25m dish, surely you just do the wavelength over 25m?

Even when I do the wavelength over 25x27 (as seen on the right) it gets a number which is out by a factor of ten?

ImageUploadedByStudent Room1434536460.304197.jpg

ImageUploadedByStudent Room1434536460.304197.jpg

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Reply 1968

Disney0702

9

For those doing Turning Points is muon decay really important?

Reply 1969

Absent Agent

21

Original post by Disney0702

For those doing Turning Points is muon decay really important?

Yes, we do need to for the evidence of time dilation, unfortunately :smile:

ImageUploadedByStudent Room1434536702.850039.jpg

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Reply 1970

Klaxoii

2

Came across this question, am I missing something because I used the equation given in the data sheet, which has (1-v^2/c^2)^-0.5, however they did not have the minus power?

ImageUploadedByStudent Room1434536709.792152.jpg

ImageUploadedByStudent Room1434536709.792152.jpg

ImageUploadedByStudent Room1434536727.305178.jpg

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Reply 1971

SuperMushroom

9

Can someone explain where equation Theta = Sr comes from??
i dont understand how it makes sense when using it in calculations and what do the S and r represent??

thanks

Reply 1972

CD223

OP

10

Original post by SuperMushroom

Can someone explain where equation Theta = Sr comes from??
i dont understand how it makes sense when using it in calculations and what do the S and r represent??

thanks

http://www.mathwarehouse.com/trigonometry/radians/s=r-theta-formula-equation.php

For a small angle approximation, the arc length is almost like a triangle, meaning we can simply treat it as theta = S/r

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Reply 1973

SuperMushroom

9

Original post by CD223

http://www.mathwarehouse.com/trigonometry/radians/s=r-theta-formula-equation.php

For a small angle approximation, the arc length is almost like a triangle, meaning we can simply treat it as theta = S/r

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Ill have a look at this now, thanks

Reply 1974

you-only-live-once

2

anyone doing medical option?

Reply 1975

Absent Agent

21

Original post by Klaxoii

Came across this question, am I missing something because I used the equation given in the data sheet, which has (1-v^2/c^2)^-0.5, however they did not have the minus power?

ImageUploadedByStudent Room1434536709.792152.jpg

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That's very strange. Which paper is that?

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Reply 1976

CD223

OP

10

Original post by SuperMushroom

Ill have a look at this now, thanks

No worries!

Reply 1977

MangoFreak

17

Not feeling this at all. I just hope my university doesn't question why I want to major in Physics when Physics ends up being my worst A Level :lol:

(edited 8 years ago)

Reply 1978

Klaxoii

2

Original post by Mehrdad jafari

That's very strange. Which paper is that?

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I'm not sure of the specific paper, it's on the physicandmathstutor.com website, in the special relativity questions, I think it's old syllabus however

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Reply 1979

gcsestuff

2

Original post by Klaxoii

I'm not sure of the specific paper, it's on the physicandmathstutor.com website, in the special relativity questions, I think it's old syllabus however

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What's the tutor is turning points 6 on your tabs can j just ask

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AQA Physics PHYA5 - Thursday 18th June 2015 [Exam Discussion Thread]

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