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

1. (Original post by QueNNch)
Guys are we allowed to write on the Section A multiple choice question paper so that we can do the calculations?

Also is it okay to underline words in the questions?

I never did these things just in case until now that I feel the need to, for this exam.
Yeah as long as your answer is clear in the box then you're all good, i scrawl all over mine with workings out haha
2. Thank you, I'm just confused about how you went from V^2/(V-2)^2 to V = 2V -4 on q19?
3. (Original post by davidharris96)
Do you mean when they'll next be in phase? Do the time period difference multiplied by the smallest time period, this gives the number of the smallest time periods that take place, then you multiply by the time period to get the overall time
Thanks for this answer, its come up twice and this helps loads
4. (Original post by Brianna96)
Hi, quick question, if anyone could answer it for me, it would be a great help!!
Why in a MS does it say E proportional to V squared in the equation of energy stored in a capacitor? Why can't you use V is proportional to E because of the equation: E=0.5QV? How do you now what equation to use when working out what is proportional to what in the energy equations?

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that eqn is for energy stored in a capacitor.

5. What are people feeling that the 6 mark written question will be on?
6. Right, I'm off for tonight. I'll see you guys after the exam tomorrow.

Best of luck!
7. Could someone explain why the answer to this question (question 4bi) is 7.4x10^11? When I did it I got 7.4x10^8
Thank you, I'm just confused about how you went from V^2/(V-2)^2 to V = 2V -4 on q19?
I tend to skip steps sorry.

Square root both sides, times both sides by (V-2)
9. (Original post by mrno1324)
What's the difference when dropping a magnet through a copper tube and a coil, if there is any?
none that i can think off.

Both would experince a mag field.
10. (Original post by mrno1324)
What's the difference when dropping a magnet through a copper tube and a coil, if there is any?
My best guess would be that as a coil has more turns (N is higher) than for a tube (which has only 1), the magnitude of induced emf would be higher?
11. (Original post by JaySP)
I tend to skip steps sorry.

Square root both sides, times both sides by (V-2)
Ah that makes sense now, thanks. Are you prepared for tomorrow?
12. (Original post by Humza Ali)
How to work out when a set of swings of varying time period will next be "in conjunction"?
The short answer is to find the lowest common multiple.

If you can't do that (or have to explain how you got to your answer), first calculate the phase difference (in seconds).

Then either work out what you must multiply the phase difference by to get to the larger of the two time periods. Then multiply the SMALLER time period by that number.

OR work out what you must multiply the phase difference by to get to the smaller of the two time periods. Then multiply the LARGER time period by that number.

For example, I think it was in june 2014 where one system had a time period of 2s and the other 1.90s. So the phase difference is 0.1s. To get to 1.90s, multiply 0.1 by 19. Then 2 * 19 = 38s.
13. (Original post by Plasmapause)
Could someone explain why the answer to this question (question 4bi) is 7.4x10^11? When I did it I got 7.4x10^8
change in W = m x change in V
change in V = +61.3 MJ =

change in W = 1.2x10^4 x 61.3x10^6
= 7.4x10^11 J
14. (Original post by Fvthoms)
Cheers 👍

Edit: Vid was just what I needed. Repped.
Hey no problem
15. Good luck everyone I'm finished now! Hope it all goes well

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16. (Original post by Plasmapause)
Could someone explain why the answer to this question (question 4bi) is 7.4x10^11? When I did it I got 7.4x10^8
1.2x10^4 ( -1.3x10^6 - -62.6x10^6 ) = 7.356x10^11 = 7.4x10^11

gravitation potential needs to be POSTIVE so add the highest potential to the lowest negative one.
Ah that makes sense now, thanks. Are you prepared for tomorrow?
I think so. I don't know what else to really go over. Yourself?
18. (Original post by Lau14)
My best guess would be that as a coil has more turns (N is higher) than for a tube (which has only 1), the magnitude of induced emf would be higher?
I think it's actually the opposite. The coil is like infinitely many turns squeezed together. We actually dropped a magnet in such a tube in school and it took a really long time to come out on the other side. Think it has to do with eddy currents being generated round the circumference of the tube.
19. Can someone help me with the equation emf=BANωsinωt. Most of the time its used it's only BANωt, what is the sinωt all about???
20. (Original post by Brianna96)
Hi, quick question, if anyone could answer it for me, it would be a great help!!
Why in a MS does it say E proportional to V squared in the equation of energy stored in a capacitor? Why can't you use V is proportional to E because of the equation: E=0.5QV? How do you now what equation to use when working out what is proportional to what in the energy equations?

Posted from TSR Mobile
You can use any of the three energy stored on a capacitor question it all depends on what values are known. As for their definitions E is proportional to the product of the capacitance and the square of voltage as well as it being proportional to the product of the charge stored and voltage. You can mathematically derive the equation from one another but they essentially mean the same thing I guess...

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