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

1. (Original post by NEWT0N)
Ha ha ha, I have not become this merry since the time when one of my students had the audacity to ask "what use is this book Euclid's Elements?" Funny lad.

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2. (Original post by NEWT0N)
God is the first and last cause, a most subtle gravitational spirit that pervades all and lies hid in all gross bodies.
So then why just as the world was created from dark chaos through the bringing forth of the light and through the separation of the airy firmament and of the waters from the earth, our work brings forth the beginning out of black chaos and its first matter through the separation of the elements and the illumination of matter?

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3. (Original post by a.a.k)

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I am much obliged for the amusement you provided me.
4. (Original post by NEWT0N)
I am much obliged for the amusement you provided me.
Most welcome. Perhaps someday you might return my favour in some other form.

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5. Hi guys I need help on doing this question as I find it really difficult, could someone please post an answer on this question so I could see how you worked it out in each step. I need to know how to do I would appreciate it if anyone could.
Thanks(urgently)
q1)Pyrometers are used to measure the temperature of substancesremotely where direct measurement is not practical or possible. One suchexample is measuring the temperature of blast furnaces in steel making. Theyuse Stefan’s Law to calculate the temperature based on the amount of energyreceived. If the amount of energy received by the pyrometer is 7.01x105Wm-2calculate the temperature of the furnace in °C. Stefan’s Constant, σ, = 5.7x10-8Wm-2K-4.
q2)
1. Blast furnaces are made from steel andlined with refractory bricks to keep as much heat energy in and to prevent thefurnace from melting. If the temperature within the furnace is as above, thethermal conductivity of the refractory brick is 1.4, the thermal conductivityof the steel is 43, the thickness of the protective brick lining is 1m, thethickness of the steel casing is 500mm, and the energy transferred through bothlayers is as above, calculate the temperature at the boundary of the lining andthe casing if the outside temperature of the blast furnace is 50°C.
6. Hi guys I need help on doing this question as I find it really difficult, could someone please post an answer on this question so I could see how you worked it out in each step. I need to know how to do I would appreciate it if anyone could.
Thanks(urgently)
q1)Pyrometers are used to measure the temperature of substancesremotely where direct measurement is not practical or possible. One suchexample is measuring the temperature of blast furnaces in steel making. Theyuse Stefan’s Law to calculate the temperature based on the amount of energyreceived. If the amount of energy received by the pyrometer is 7.01x105Wm-2calculate the temperature of the furnace in °C. Stefan’s Constant, σ, = 5.7x10-8Wm-2K-4.
q2)
1. Blast furnaces are made from steel andlined with refractory bricks to keep as much heat energy in and to prevent thefurnace from melting. If the temperature within the furnace is as above, thethermal conductivity of the refractory brick is 1.4, the thermal conductivityof the steel is 43, the thickness of the protective brick lining is 1m, thethickness of the steel casing is 500mm, and the energy transferred through bothlayers is as above, calculate the temperature at the boundary of the lining andthe casing if the outside temperature of the blast furnace is 50°C.
7. (Original post by NEWT0N)
Hint: Unit 2 wave theory (nodes, etc.)

Yes, it's sad how they expect you to remember AS physics because most people forget the unnecessary details (ones that aren't "built on" in A2) after a while. If they insist on including AS stuff, I would much prefer if they did AS+A2 in one paper at the end of A2. Having it so far away from the A2 paper and still expecting everyone to know it is silly.
Yes it is annoying that they want us to remember AS knowledge.

But I still do not understand the question. I wasn't particularly good at Unit 2.
8. 3 full days of smashing unit 4. I can't wait

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9. Hello everyone, I've done the JAN '11 paper and I've come upon questions that I were stuck and I was wondering if you could help me.

Section A - Q14, Q21 and Q24.

Section B - Q5(c)

10. (Original post by Disney0702)
Hello everyone, I've done the JAN '11 paper and I've come upon questions that I were stuck and I was wondering if you could help me.

Section A - Q14, Q21 and Q24.

Section B - Q5(c)

for 14 use F=EQ and F=ma with the values of q and m for an election, for 21 use linkage=BANCostheta and subtract the values at 0 and 50 and for 24 you need to consider how a transformer works if voltage increases then current decreases and the secondary coil has more turns so there more flux linkage.

Question 5c goes right back to unit 2 where the fundamental harmonic was one loop and thus wavelength/2 shove the numbers in the formula(v=frequency*wavelength) to see it does give the fundamental vibration and thus resonates.
11. @NEWT0N; did you manage to work out the final question in my last post?
12. (Original post by Dalek1099)
for 14 use F=EQ and F=ma with the values of q and m for an election, for 21 use linkage=BANCostheta and subtract the values at 0 and 50 and for 24 you need to consider how a transformer works if voltage increases then current decreases and the secondary coil has more turns so there more flux linkage.

Question 5c goes right back to unit 2 where the fundamental harmonic was one loop and thus wavelength/2 shove the numbers in the formula(v=frequency*wavelength) to see it does give the fundamental vibration and thus resonates.
Thank you for your explanations, they've really helped.

I'm afraid I'm still a little confused on Q5(c), I know it is Unit 2 but I jut cannot understand this question.

Would it be too much to ask if you could do a step by step detailed explanation because I do not see how I can explain how a large amplitude vibration is produced.

13. Can someone explain Q1(a)(ii) from JUN '11.

Why is R = mg - mv2/r

I assumed it'd be R = mg + mv2/r

As weight and centripetal force acts in the same direction.
14. (Original post by Disney0702)
Can someone explain Q1(a)(ii) from JUN '11.

Why is R = mg - mv2/r

I assumed it'd be R = mg + mv2/r

As weight and centripetal force acts in the same direction.

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15. (Original post by Disney0702)
Can someone explain Q1(a)(ii) from JUN '11.

Why is R = mg - mv2/r

I assumed it'd be R = mg + mv2/r

As weight and centripetal force acts in the same direction.
No, the centripetal force IS Mg-R. Therefore, you can say Mg-R = Mv^2/r and hence R = mg-mv^2/r. I made this mistake too
16. That photo has just solved 3 days of issues thanms

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17. (Original post by gcsestuff)
That photo has just solved 3 days of issues thanms

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Haha ikr

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18. (Original post by issy_246)
Hi guys I need help on doing this question as I find it really difficult, could someone please post an answer on this question so I could see how you worked it out in each step. I need to know how to do I would appreciate it if anyone could.
Thanks(urgently)
q1)Pyrometers are used to measure the temperature of substancesremotely where direct measurement is not practical or possible. One suchexample is measuring the temperature of blast furnaces in steel making. Theyuse Stefan’s Law to calculate the temperature based on the amount of energyreceived. If the amount of energy received by the pyrometer is 7.01x105Wm-2calculate the temperature of the furnace in °C. Stefan’s Constant, σ, = 5.7x10-8Wm-2K-4.
q2)
1. Blast furnaces are made from steel andlined with refractory bricks to keep as much heat energy in and to prevent thefurnace from melting. If the temperature within the furnace is as above, thethermal conductivity of the refractory brick is 1.4, the thermal conductivityof the steel is 43, the thickness of the protective brick lining is 1m, thethickness of the steel casing is 500mm, and the energy transferred through bothlayers is as above, calculate the temperature at the boundary of the lining andthe casing if the outside temperature of the blast furnace is 50°C.
So r u being serious or just trolling

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19. Can anyone help me with Qus 3 and 20 in part A June 2014 please?
20. Just have to remember that the positive signs are ones that always act towards the centre

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