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# AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] watch

1. (Original post by Sbarron)
Attachment 425971

Does this help visually?? (Sorry about the lack of artistic skills!) ha
In the first picture the wire/magnet should be moving upwards but can't.... In the second picture the wire/magnet wants to move down but can't
2. Where did the 1560Vm-1 value for Electric field strength come from?
3. I just want to know about the 0.121V question now! Question 4 part c I think?
4. (Original post by jordan_bennett14)
I just want to know about the 0.121V question now! Question 4 part c I think?
EMF=Change in BAN / Change in Time

BAN goes to zero after 90degree turn so EMF = 0.0605/0.5
5. (Original post by DysonCube)
EMF=Change in BAN / Change in Time

BAN goes to zero after 90degree turn so EMF = 0.0605/0.5
i left it as 2 sf, will that still get me the marks?
6. (Original post by muhts)
i left it as 2 sf, will that still get me the marks?
If the data was given to 2sf then it should.
7. (Original post by Cmog)
I did the same as you chazley
I thought physicists liked to keep things simple aye
8. (Original post by davidharris96)
Are you agreeing with me that its D? (rate of change in momentum)
was D weight? if so then yes
9. Anybody know about the Field strength question?
10. (Original post by CD223)
This thread has been great for answering each other's questions and helping one another out. I personally feel like the MC was a lot easier due to this thread. Thanks for that everyone!

Let's smash PHYA5 now - perhaps the number of posts on that thread can't beat this in 6 days though 😂😂

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I agree! Before discovering this thread I scored no more than 12/25 on Section A. But thanks to many people on this Physics thread my methods on how to tackle them have really improved. Couldn't have done it without you guys.

Good luck with PHYA5
11. (Original post by DysonCube)
Anybody know about the Field strength question?
In multiple choice?
12. (Original post by Disney0702)
In multiple choice?
No, the one in section B with the graph where it asks you to work out the field strength at 0.4m. I got 1875Vm-1 but the MS on here says 1560Vm-1.
13. (Original post by jordan_bennett14)
I also noticed that, it was June 2010. I still don't understand why it isn't zero though instead of double the negative value (-332g). I understand the maths but logically I don't understand why the wire going the other way can be detected by the balance. I think I'm misunderstanding something here lol :P
Ok. I hope this will dispel your confusion.

The questions said that the scale was zeroed after the magnet was placed on the scale. This means that when the magnet was placed on the scale, the scale read the mass of the magnet before it was zeroed( you don't know the mass of the magnet). So when the current was flowing through the wire, the magnetic field produced by the wire exerted a force on the magnet( and essentially on the scale), equivalent to 161g. Therefore when the switch is off , that is no current flowing through the wire, the scale would read zero as there is no force exerting on the scale and also that the scale was zeroed. But you know that particular current produced a force equal to the weight of 161g( that's why the scale read this value when the current was on). So it follows that when the current is reversed and doubled the magnetic force produced is able to lift a mass equal to twice of 161g, that is 322 grams.
Your confusion arises here. Because the scale was zeroed after the magnet was placed on the scale, the scale would read negative of the mass of the magnet if you were to take the magnet off the scale. So in the case of the question the mass of the magnet was assumed to be greater than 322g because if the mass of the magnet was less than that then after reversing and doubling the current, the magnetic field produced by the wire would lift the magnet off the scale completely and the scale would only read the negative of the mass of the magnet, that's less than -322g because the scale was zeroed beforehand.

So the scale read negative because, after reversing and doubling the current, the magnetic force of the the wire was able to lift the magnet of the scale as if you are taking the magnet off the scale.

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14. How do you do 2D, the work done question??
15. Hey guys if you didn't know there's an unofficial mark scheme on page 1 !

I looks like I could lose a maximum of 15 marks in the exam. Meaning I'll get ~60 marks. Would that be an A what do y'all think?
16. Well I don't think the full UMS cap can be predicted at all much because they've been rising since the past couple of years , as students are able to perform better due to lots of past papers available even though the exam becomes slightly more difficult.

In my school the clever ones really liked the paper and thought it was easy :s

Now I'm expecting around the same (maybe 2 marks lower) boundaries compared last year.
17. Wouldnt the emf induced be 4.8?
18. (Original post by MSB47)
Wouldnt the emf induced be 4.8?
I got 0.12
I think it was the use of simple V=IR or P=VI

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19. Yh i got 0.12 aswell
20. For the coil that rotated 90 degrees?

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