# OCR Physics A G485 - Frontiers of Physics - 18th June 2015Watch

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4 years ago
#81
(Original post by Makashima)
I wasnt referring to the solenoid N/S poles but just a constant magnetic field and a loop of wire, but thanks anyway

For solenoid I suppose you refer to magnetic flux because the magnet is at 90 degree thus no need to talk about magnetic flux linkage

Sorry shouldve been cleaaar

But I suppose the answer is different for both the N/S solenoid and constant field+wire?

Because for the constant B field, I would use flux linkage instead of flux, because the area is changing? Is this correct Hmmm

Hmmm Idk, sorry

Btw thanks for explaining the solenoid, I finally understand it...I actually gave up to understand the concept yet you helped to understand much better than my teacher lmao

So what should I refer to linkage or flux only

the reason why im saying linkage instead of flux because as a the loop of wire goes in , the amount area of wire goes in is increasing so there is a change in magnetic linkage

idk

halp meh pls
Are you talking about a single wire or a loop/coil of wire, you seem to be referring to both in this post and the last one.

EDIT: Just realized you are talking about a coil of wire.
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4 years ago
#82
(Original post by Makashima)
For solenoid I suppose you refer to magnetic flux because the magnet is at 90 degree thus no need to talk about magnetic flux linkage
You should refer to magnetic flux linkage, because a solenoid is just a coil of wire wound round a conductive core, so it has a certain number of turns N and thus has magnetic linkage, also recall the definition of Faraday's Law, the induced emf is directly proportional to the rate of change in magnetic flux linkage. Also recall that in order to generate electricity you only need relative motion of a conductor and magnetic field to generate electricity. (I AM NOT 100% CERTAIN), but surely this then means even if you had a stationary magnet, and moved the solenoid then the same process as the other person stated will occur. As think about it, moving the solenoid will still cause the same linkage, as would have keeping the solenoid stationary and moving the magnet. So I think you can just apply this reasoning to your situation. PLEASE CORRECT ME IF I AM WRONG.
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4 years ago
#83
thanks guy, sorry im so confusing >
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4 years ago
#84
(Original post by Makashima)
Can someone explain the process of a loop wire going into a magnetic field and refer to Faradays Law, my notes are completely messy thus wrong :L

Heres what I conclude so far

o As wire goes in, the area in t
he magnetic field increases so theres a change in magnetic flux linkage (NBA) thus emf is induced but in opposite direction (?) hence it is negative

o but when it is fully in the magnetic field, theres no change in magnetic flux linkage because N,B,A is all constant

o as it leaves the magnetic field, the area within the magnetic field decreases instead thus ...idk then something emf positive
Sorry, back again. However I think I can explain it precisely for your situation.

Recall that the magnetic flux linkage is the magnetic flux density x the number of turns of the coil x the area of the coil perpendicular to the flux density i.e.

and recall that induced e.m.f.= - delta(phiN)/delta(t)
(and throughout lets assume that the coil is always perpendicular to the magnetic field, so we don't need to consider components, and that N=25 and B=0.25)

As the coil first enters the field the magnetic flux linkage increases, this is because the area perpendicular to B increases, and as Faraday's Law states, an emf will be induced.

Now, lets assume

At t=0 the coil is outside of the magnetic field, hence (it should be easy to see) that the magnetic flux linage is 0
At t=2 the coil is entering the field, lets say that the area in the field is 2 unit^2 and B=0.25 and N=25, so the magnetic flux linkage is (2)(0.25)(25)=6.25
So over this two second period the induced e.m.f. will be -(12.5-0)/(2-0)=-6.25V

Later on at t=3 the coil is fully in the field, lets say that A=4 unit^2 B=0.25 and N=25, so the flux linkage is (0.25)(25)(4)=25 and that at a later time t=7 the coil is still fully in the field, so the flux linkage will again be 25. So over this 4 second period the induced e.m.f. will be -(25-25)/(7-3)=0V.

Lets think about this once the coil is fully in the field the area of the coil perpendicular to B will be the same, regardless of the time it is fully in the field, so there will be no rate of change in flux linkage and thus no induced e.m.f.

As the coil leaves the magnetic field there is a decrease in the flux linkage, the e.m.f will be in the reverse direction compared to previously, this can be explained via Lenz's Law and the person who wrote the post about the solenoid explains this.

Hope this clears it up for you!

EDIT: If you have the official OCR text book having a look at question 18 on page 149 may prove beneficial and the answer is on page 298
2
4 years ago
#85
(Original post by Tiwa)
Did you guys find these papers?
I'm going back to school on Tuesday so I'll ask my teacher then.

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4 years ago
#86
HI guys. I would also be grateful if you could find OCR june 14 papers. I have access to AQA june 14 papers so if you guys want any just let me know.
thanks
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4 years ago
#87
HI guys. I would also be grateful if you could find OCR june 14 papers. I have access to AQA june 14 papers so if you guys want any just let me know.
thanks

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4 years ago
#88
(Original post by lollipopsftw)

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wOULD you mind me the link plz ?
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4 years ago
#89
(Original post by lollipopsftw)

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Could you please PM me the links as well? I would really appreciate it!
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4 years ago
#90
(Original post by lollipopsftw)

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If you could send me the 2014 ocr series for g482 g484 and g485 as well that would be much appreciated.
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4 years ago
#91
Guys as soon as I get the OCR June 2014 papers I'll message them to you. Expected to get them on Tuesday/wednesday when I go back to school.
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4 years ago
#92
Guys im going to post a graph showing the grade boundaries over the years to give us an indicative prediction as to what the paper will be like this year. will post in a bit (for g485 and g484)
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4 years ago
#93
here you go guys
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4 years ago
#94
(Original post by lollipopsftw)
Guys im going to post a graph showing the grade boundaries over the years to give us an indicative prediction as to what the paper will be like this year. will post in a bit (for g485 and g484)
That's amazing, thanks! Could you modify your graph easily to show the A* boundaries? If not don't worry

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4 years ago
#95
(Original post by Elcor)
That's amazing, thanks! Could you modify your graph easily to show the A* boundaries? If not don't worry

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yeah sure i'll try do it for today
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4 years ago
#96
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4 years ago
#97
(Original post by lollipopsftw)
x
Hey it's me again :P Can you do one for B grade please, if not then that is fineee

------------
Do we need to know the definition of an antiparticle? Teacher hasnt taught us but it came up in a 2007 paper but then it is a 2007 How would you define it? Thanks
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4 years ago
#98
I have both the 2014 papers and mark schemes for you guys!
https://www.mediafire.com/folder/zfm...2zdfkqj/shared
3
4 years ago
#99
(Original post by FeelsToWaltz)
I have both the 2014 papers and mark schemes for you guys!
https://www.mediafire.com/folder/zfm...2zdfkqj/shared
That's just brilliant.
1
4 years ago
#100
I also have the AS papers if anyone is redoing them: https://www.mediafire.com/folder/p2j...1372d6v/shared
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