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OCR PHYSICS B G495~ 18th June 2015 AM ~ A2 Physics

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Original post by Minecraft27
2312 kelvin. Don't know if that's right or not.


can you remember your method for it? weirdly mine involved having to log both sides, but don't know whether that's a more complex method and if there was a simpler way?
Original post by STATER
2800 or something close to that
Edit: I don't remember well. Only that it was the same 1st SF


what'd mean first sf? I got it as 2312K I think :smile:
When the crack appeared I wrote that air has a less permeability than iron therefore the flux went down but the density stayed the same.
Original post by STATER
2800 or something close to that
Edit: I don't remember well. Only that it was the same 1st SF


I got something like that, but my method was wrong haha I had few minutes at end and i used relationship that Boltzmann factor increases by power of 10 for a double in temperature and just done 2200x2^(3/10). Pretty sure I'm wrong cos it just makes no sense to me even now haha.
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STATER
3
Original post by HennersPD
what'd man first sf? I got it as 2312K I think :smile:


Same significant figure as the original given temperature which was 2000K ?
Original post by HennersPD
it stopped the flow of flux in the core, so the flux decreased and due to air being a good insulator, the flux density unchanged :smile:


I don't think an air gap stops flux from flowing, magnetic circuits can still work if there is an air gap, it's just air has a lower permeability? It's not so low that it stops it from flowing, such as its electrical conductivity.
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STATER
3
Original post by RealTime
I got something like that, but my method was wrong haha I had few minutes at end and i used relationship that Boltzmann factor increases by power of 10 for a double in temperature and just done 2200x2^(3/10). Pretty sure I'm wrong cos it just makes no sense to me even now haha.


I did N=ke^...
Found N/k using given values

3N/k = e^...

Found T
Original post by RealTime
I got something like that, but my method was wrong haha I had few minutes at end and i used relationship that Boltzmann factor increases by power of 10 for a double in temperature and just done 2200x2^(3/10). Pretty sure I'm wrong cos it just makes no sense to me even now haha.


I used the fact current was proportional to the boltzmann factor and workout the current for 3N as 3*the current from part a , then did the log of both sides to cancel the e^-E/kT then just rearranged for T to get 2312K :smile: seems quite complex for 3 marks haha
Original post by STATER
I did N=ke^...
Found N/k using given values

3N/k = e^...

Found T


yeah thats basically what I did :smile:
Original post by STATER
I did N=ke^...
Found k using given values

3N/k = e^...

Found T


Yeah I was being an idiot, differentiated the thing instead of just equating cos I was like hmm yeah current is flow of electrons so rate of electrons must be differential of RHS of relationship. I know whatever I done was wrong though, but meh no more exams not worth worrying about it.
Original post by RealTime
I don't think an air gap stops flux from flowing, magnetic circuits can still work if there is an air gap, it's just air has a lower permeability? It's not so low that it stops it from flowing, such as its electrical conductivity.


ah yes of course, i actually put that both flux and flux density decrease due to the crack, was purely curious as to why it couldn't be explained using permeability :smile:
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STATER
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Original post by RealTime
I know whatever I done was wrong though, but meh no more exams not worth worrying about it.


How did your other exams go?
Original post by HennersPD
yeah thats basically what I did :smile:


Same. I worked out the value of N, then x3 then re-did the calc to get 2312.

I don't think 2800 is right.
Original post by RealTime
Yeah I was being an idiot, differentiated the thing instead of just equating cos I was like hmm yeah current is flow of electrons so rate of electrons must be differential of RHS of relationship. I know whatever I done was wrong though, but meh no more exams not worth worrying about it.


yeah and plus you could've easily have made the marks up else where :smile: don't worry just enjoy summer whilst it lasts :P
Original post by STATER
How did your other exams go?


smashed maths, chem went bad for me cos it's my best subject but didn't do well as I was expected and physics was OK, bad thing is I need 252 UMS to make the A so hopefully I will get it
For the x and y bit did you divide one by 4 and one by 16?


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Original post by Minecraft27
Same. I worked out the value of N, then x3 then re-did the calc to get 2312.

I don't think 2800 is right.


yeah because you already worked out N from the first part using the current and charge on the electron, multiply this by 3 and rearrange by logging both sides to find T as 2312K which to me a time seemed like a plausible answer haha :smile: as a greater current flows obviously the temperature would increase from 2200K as more electrons, more collisions, more energy dissipated so temperature increases! Phew, glad i worked that one out :wink:
Original post by Mutleybm1996
For the x and y bit did you divide one by 4 and one by 16?


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Yes.
Original post by Mutleybm1996
For the x and y bit did you divide one by 4 and one by 16?


Posted from TSR Mobile


That sounds familiar yes :smile:
I got 2300K to 2SF as the information was to 2 SF, is that wrong?

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