The Student Room Group

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

Scroll to see replies

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?


Posted from TSR Mobile

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.


Posted from TSR Mobile
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.


Posted from TSR Mobile


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!


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

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

Thank you in advance.
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 :biggrin: 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!
Original post by Disney0702
Can someone please explain Q1(b)(iii) from Jun '12 Section B.

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

Thank you in advance.


Uploaded a solution to that a few days ago. Here's the link:

http://www.thestudentroom.co.uk/showthread.php?t=3047347&page=109&p=56336639&highlight=#post56336639

Let me know if you need any help/can't read my messy handwriting :biggrin:
Original post by _Caz_
We have the same calculators haha :biggrin: 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!


Lol yeah, and it has a backlight! For when you're furiously calculating at night :colone:
ImageUploadedByStudent Room1433775757.244349.jpg

Can someone give me a hint on what to do please


Posted from TSR Mobile
Original post by Protoxylic
Lol yeah, and it has a backlight! For when you're furiously calculating at night :colone:


casio knows we maths people too well :'D
Reply 2968
3000+ posts! You guys really do love physics :biggrin:


Posted from TSR Mobile
Original post by gcsestuff
ImageUploadedByStudent Room1433775757.244349.jpg

Can someone give me a hint on what to do please


Posted from TSR Mobile


I struggle with these questions too. There is a way of doing them though and I don't understand it but it works.

find the difference between the two time periods.

If it wants the number of oscillations of the one with the longer time period, divide the value of the shorter time period by the difference between the two time periods.

If it wants the number of oscillations of the one with the shorter time period, divide the value of the longer time period by the difference between the two time periods.

I know this wasn't exactly what you were looking for and I really struggle to get my head around these too but that method works every time :smile:
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,

Sorry I'm bad at explaining...haha

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

Posted from TSR Mobile


I think you're very wrong for the first one and I definitely think it is 'C'. My reasoning is that if you go to a maximum value of current then switch it off, then that will be the greatest change in the coil X's magnetic field produced since it goes to a maxima to nothing. Therefore, the other coil will cut the coil 'X' field lines at the fastest rate for this event out of all the other events listed and hence that will induce highest emf for other coil and thus highest reading on the ammeter.
Original post by _Caz_
I struggle with these questions too. There is a way of doing them though and I don't understand it but it works.

find the difference between the two time periods.

If it wants the number of oscillations of the one with the longer time period, divide the value of the shorter time period by the difference between the two time periods.

If it wants the number of oscillations of the one with the shorter time period, divide the value of the longer time period by the difference between the two time periods.

I know this wasn't exactly what you were looking for and I really struggle to get my head around these too but that method works every time :smile:


Mate that's perfect thanks! Hope it comes up now!!!


Posted from TSR Mobile
Reply 2972
Original post by adil1231
I think you're very wrong for the first one and I definitely think it is 'C'. My reasoning is that if you go to a maximum value of current then switch it off, then that will be the greatest change in the coil X's magnetic field produced since it goes to a maxima to nothing. Therefore, the other coil will cut the coil 'X' field lines at the fastest rate for this event out of all the other events listed and hence that will induce highest emf for other coil and thus highest reading on the ammeter.


Yeah that's true.


Posted from TSR Mobile
Cd did you ask your teacher about the gravity question regarding orbits?


Posted from TSR Mobile
Everyone's saying the biology unit 4 paper contained all unit 1 and 2 questions. I hope that won't happen to us, but then I guess that's what's gonna happen over the coming years with one paper sat at the very end


Posted from TSR Mobile
Original post by _Caz_
I struggle with these questions too. There is a way of doing them though and I don't understand it but it works.

find the difference between the two time periods.

If it wants the number of oscillations of the one with the longer time period, divide the value of the shorter time period by the difference between the two time periods.

If it wants the number of oscillations of the one with the shorter time period, divide the value of the longer time period by the difference between the two time periods.

I know this wasn't exactly what you were looking for and I really struggle to get my head around these too but that method works every time :smile:


There was a difference of 0.1, beween T1 = 2 and T2 = 1.9, but the answer was 38 not 19, whY?
Reply 2976
Original post by gcsestuff
Cd did you ask your teacher about the gravity question regarding orbits?


Posted from TSR Mobile


Yeah only just got a reply today!

"Radius" means use that figure. "Height" means add the radius to the distance given.



Posted from TSR Mobile
Original post by AR_95
There was a difference of 0.1, beween T1 = 2 and T2 = 1.9, but the answer was 38 not 19, whY?


2 doesn't go into 19, so it must be doubled
Reply 2978
Does anyone have any notes specifically for the wordy, 6 mark questions? Any help is much appreciated lol
Original post by adil1231
I think you're very wrong for the first one and I definitely think it is 'C'. My reasoning is that if you go to a maximum value of current then switch it off, then that will be the greatest change in the coil X's magnetic field produced since it goes to a maxima to nothing. Therefore, the other coil will cut the coil 'X' field lines at the fastest rate for this event out of all the other events listed and hence that will induce highest emf for other coil and thus highest reading on the ammeter.


Yeah, actually you're right. But man you can't be going around telling people they are 'very wrong', the exam is in 3 days and my confidence has just gone from 100 to 0...haha

Quick Reply

Latest