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

1. For question 3 use (rate^2* density)/area

2. I can understand how to get part c ii. I found the distance between them but then it's makes the energy required equal to v

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3. I'm also stuck on these 2

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4. (Original post by gcsestuff)

I can understand how to get part c ii. I found the distance between them but then it's makes the energy required equal to v

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I couldn't make sense of the first method they use but i would suggest you stick with the method you understand. This method is the same as the second method of the mark scheme

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5. (Original post by gcsestuff)

I'm also stuck on these 2

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The top one is 'B'.Electromagnetic induction only happens, in this case, when the magnitude or direction of flux changes. When the current is increasing, there's em induction going on, when its constant nothing happens,

The other one...come on, that's pretty straight forward
GMm/r^2 = mv^2/r where M is the mass of the sun and m the mass of the earth,r is the distance, = radius of earth + orbital radius + radius of the sun

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6. Can someone please explain Q5(c) from Jan '11 Section B

I keep struggling with it.

Is natural frequency the same as fundamental frequency?
7. (Original post by Mehrdad jafari)
You need to equate the force exerted by the sun on the earth keeping the earth in its orbit.
The distance from the centre of the sun to the centre of the earth, the radius of the orbit, is given to you.
Attachment 420775

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That's what I did but I don't get the correct answer. I may be using the wrong value for r. I thought r would be the radius of the orbit + the radius of the earth?
8. What type of calculator does everyone plane to use during this exam?
9. (Original post by lebanon95)
What type of calculator does everyone plane to use during this exam?
I used to take both my scientific calculator from gcse and my graphical calculator that I have for maths but now I'm more used to the graphical one (and it's a lot easier to do big equations on because you can see more at once) so I just take that.
10. (Original post by Disney0702)
Can someone please explain Q5(c) from Jan '11 Section B

I keep struggling with it.

Is natural frequency the same as fundamental frequency?
Yes, the fundamental mode of vibration of a string is such that the length of the string is half the wavelength. And when the string vibrates in this mode, this frequency is also the natural frequency of the string. So if a periodic driving force is applied at that frequency, the string resonates.
11. (Original post by lebanon95)
What type of calculator does everyone plane to use during this exam?
A graphical (Casio fx-9860GII) and scientific (Casio fx 991 es plus). Sadly I will have to part ways with my graphical calculator as I head to uni; they aren't permitted in exams.
12. (Original post by Protoxylic)
A graphical (Casio fx-9860GII) and scientific (Casio fx 991 es plus). Sadly I will have to part ways with my graphical calculator as I head to uni; they aren't permitted in exams.
What do you use the graphical one for ? My brother has a casio fx-cg 20 wondering if i should take it in or not.
13. (Original post by tawaz1997)
The top one is 'B'.Electromagnetic induction only happens, in this case, when the magnitude or direction of flux changes. When the current is increasing, there's em induction going on, when its constant nothing happens,

The other one...come on, that's pretty straight forward
GMm/r^2 = mv^2/r where M is the mass of the sun and m the mass of the earth,r is the distance, = radius of earth + orbital radius + radius of the sun

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Thanks!!

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14. Guys,
Here is the answer sheet for the multiple choice section. you must do all your rough work of the multiple choice section on the question paper and then choose the correct answer on this sheet.
Attached Images
15. OTQ 01_no trims.pdf (271.9 KB, 159 views)
16. (Original post by lebanon95)
What do you use the graphical one for ? My brother has a casio fx-cg 20 wondering if i should take it in or not.
There isn't really anything you can use it for in Phys4. I just use it to verify answers in maths.
17. Can someone say if I'm right or wrong. For transformers in a step up transformer does the voltage increase as there are more bindings on the secondary core. So when a magnetic flux is induced in the core it cuts the bindings and produces a voltage, the more bindings the more magnetic flux induced and therefore a bigger emf?

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18. (Original post by gcsestuff)
Can someone say if I'm right or wrong. For transformers in a step up transformer does the voltage increase as there are more bindings on the secondary core. So when a magnetic flux is induced in the core it cuts the bindings and produces a voltage, the more bindings the more magnetic flux induced and therefore a bigger emf?

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By more bindings do you mean more number of turns?
A step up transformer has more number of turns on the secondary 'coil' than on the primary coil and so when the primary coil is connected to an a.c. supply an alternating magnetic field is produced is the core of the transformer. This will induce an alternating magnetic field in the secondary coil and since the secondary coil has more turns the induced emf in the secondary coil is greater(Faraday's law), than the emf supplied to the primary coil.

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19. (Original post by Mehrdad jafari)
By more bindings do you mean more number of turns?
A step up transformer has more number of turns on the secondary 'coil' than on the primary coil and so when the primary coil is connected to an a.c. supply an alternating magnetic field is produced is the core of the transformer. This will induce an alternating magnetic field in the secondary coil and since the secondary coil has more turns the induced emf in the secondary coil is greater(Faraday's law), than the emf supplied to the primary coil.

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Yeah I do!

Thanks that's what i was trying to say, you're so much better at explanations but it works in my head!

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20. Can someone please explain Q1(b)(iii) from Jun '12 Section B.

I do not understand the second step in the mark scheme.

21. (Original post by Protoxylic)
A graphical (Casio fx-9860GII) and scientific (Casio fx 991 es plus). Sadly I will have to part ways with my graphical calculator as I head to uni; they aren't permitted in exams.
We have the same calculators haha Ngl though, I hate my graphics one, only use it in further maths when I have to. It takes like three buttons to delete one line of working! (also it scares me with how much it can do)

The casio fx-911ES plus is great though!

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