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AQA PHYA4 ~ 13th June 2013 ~ A2 Physics

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Original post by bobthebuilder
yeah that's all you need to remember


wow thats so contradicting :O but i guess i will just remember that
Original post by bobthebuilder
can someone please help me out with this question?


i dont know if this is close to the right answer, probably not, but ill say what i done LOL :o:

they give the diameter of the coil, and we know that the area of a circle is πD22 \pi \frac{D}{2}^2 so if you sub in the value of D that they have given you can find out the area A, now they are asking for magnetic flux which is θ=BA \theta = BA they have given B and we worked out A, and since its perpendicular to the magnetic field then we get maximum flux and minimum emf, so thats first question done, now next it asks for flux linkage after its rotate 90 degrees, this means now the emf is maximum (parallel to field lines) and flux is minimum so the change in flux is actually the original value of flux (going from original value at max flux [90degrees] to 0 at min flux [0degrees] and then you would times by 'N' since they are asking for flux linkage THATS WHAT I THINK. for third part you would then put the calculated flux linkage and divide by the time given in the question.

if what i have said is correct, the answers should be

a) 6.93×10−46.93\times10^-4 Wb

b)i) 0.590.59 Wb turns

b)ii) 4.91 V

???????!!!!!! please be right :frown:
(edited 10 years ago)
Original post by masryboy94
wow thats so contradicting :O but i guess i will just remember that


well.. not really,just try to get this:

the direction of current flow is the OPPOSITE of the direction of electron flow.

so when you're working force on an electron, you would do the opposite of what you would do on current..

or remembering what you said before if all you need!
Original post by bobthebuilder
well.. not really,just try to get this:

the direction of current flow is the OPPOSITE of the direction of electron flow.

so when you're working force on an electron, you would do the opposite of what you would do on current..

or remembering what you said before if all you need!


but in the book they say the electric current in a wire is the flow of negatively charged electrons, is it badly worded from them?

Edit: is conventional current, in the opposite direction of electrons and current in the direction of electrons?
(edited 10 years ago)
Original post by masryboy94
but in the book they say the electric current in a wire is the flow of negatively charged electrons, is it badly worded from them?

Edit: is conventional current, in the opposite direction of electrons and current in the direction of electrons?


nope, current flow is in the opposite direction of electron flow.
if you think of a simple circuit, it shows the direction of current flow from positive terminal to negative terminal.
but electrons actually flows from negative terminal ( its repelled by the negative charge) to the positive terminal (attracted by the positive charge)
Original post by bobthebuilder
nope, current flow is in the opposite direction of electron flow.
if you think of a simple circuit, it shows the direction of current flow from positive terminal to negative terminal.
but electrons actually flows from negative terminal ( its repelled by the negative charge) to the positive terminal (attracted by the positive charge)


ahh okay makes sense, the book really confused me !! ... btw i tried answering your question earlier, not sure atall if im right ... which paper was it form? .... thanks btw :biggrin:
Original post by masryboy94
ahh okay makes sense, the book really confused me !! ... btw i tried answering your question earlier, not sure atall if im right ... which paper was it form? .... thanks btw :biggrin:


oh i know how to do part a but I'm stuck on b and c. its a really old paper so i gave up, you can try it if you want to:

http://www.tomred.org/uploads/7/7/8/3/778329/physics_u4b_qp_jan_2005.pdf

http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=13924&ResourceId=182553

it's question 4
Original post by bobthebuilder
oh i know how to do part a but I'm stuck on b and c. its a really old paper so i gave up, you can try it if you want to:

http://www.tomred.org/uploads/7/7/8/3/778329/physics_u4b_qp_jan_2005.pdf

http://www.school-portal.co.uk/GroupDownloadFile.asp?GroupId=13924&ResourceId=182553

it's question 4


yaay got it right !! .... i explained it to you on a previous post? scroll up and you will see it

edit: it asks for flux linkage after its rotate 90 degrees, this means now the emf is maximum (parallel to field lines) and flux is minimum so the change in flux is actually the original value of flux (going from original value at max flux [90degrees] to 0 at min flux [0degrees] and then you would times by 'N' since they are asking for flux linkage. for second part of b) you would then put the calculated flux linkage and divide by the time given in the question.
(edited 10 years ago)
Original post by masryboy94
i dont know if this is close to the right answer, probably not, but ill say what i done LOL :o:

they give the diameter of the coil, and we know that the area of a circle is πD22 \pi \frac{D}{2}^2 so if you sub in the value of D that they have given you can find out the area A,now they are asking for magnetic flux which is θ=BA \theta = BA they have given B and we worked out A, and since its perpendicular to the magnetic field then we get maximum flux and minimum emf, so thats first question done, now next it asks for flux linkage after its rotate 90 degrees, this means now the emf is maximum (parallel to field lines) and flux is minimum so the change in flux is actually the original value of flux (going from original value at max flux [90degrees] to 0 at min flux [0degrees] and then you would times by 'N' since they are asking for flux linkage THATS WHAT I THINK. for third part you would then put the calculated flux linkage and divide by the time given in the question.

if what i have said is correct, the answers should be

a) 6.93×10−46.93\times10^-4 Wb

b)i) 0.590.59 Wb turns

b)ii) 4.91 V

???????!!!!!! please be right :frown:


okay that makes sense thanks :smile: i did't see your answer before,i though people just ignored me

so originally it was perpendicular, and it was changed by 90 degrees so its parallel.
so the change is flux is equal to the original value of flux, but why is emf maximum when its parallel, shouldn't it be minimum?
Original post by bobthebuilder
okay that makes sense thanks :smile: i did't see your answer before,i though people just ignored me

so originally it was perpendicular, and it was changed by 90 degrees so its parallel.
so the change is flux is equal to the original value of flux, but why is emf maximum when its parallel, shouldn't it be minimum?


for a good few months i usto ask exact same question, but now i understood it, it would be so much easier to explain it if you were infront of me, but since im not, all you need to remember is that when you get maximum flux (90degrees to the magnetic field) you get minimum emf and vice versa. so basically emf and flux always do the opposite, unless in the special case the coil is 45degrees to the magnetic field, there you get them equal eachother.
Original post by bobthebuilder
okay that makes sense thanks :smile: i did't see your answer before,i though people just ignored me

so originally it was perpendicular, and it was changed by 90 degrees so its parallel.
so the change is flux is equal to the original value of flux, but why is emf maximum when its parallel, shouldn't it be minimum?


emf is maximum when the flux through the coil is 0, i.e. when the coil is parallel to the field lines, because at this point the rate of change of flux is at a maximum (and that is equal to emf).
Original post by masryboy94
for a good few months i usto ask exact same question, but now i understood it, it would be so much easier to explain it if you were infront of me, but since im not, all you need to remember is that when you get maximum flux (90degrees to the magnetic field) you get minimum emf and vice versa. so basically emf and flux always do the opposite, unless in the special case the coil is 45degrees to the magnetic field, there you get them equal eachother.



Original post by jonnyb123
emf is maximum when the flux through the coil is 0, i.e. when the coil is parallel to the field lines, because at this point the rate of change of flux is at a maximum (and that is equal to emf).


omg I am SO confused.
is it just me or do you both contradict each other?

is this very important, because i could've got the answer to that question without knowing all this minimum/maximum thing, right?
(edited 10 years ago)
Original post by bobthebuilder
omg I am SO confused.
is it just me or do you both contradict each other?

is this very important, because i could've got the answer to that question without knowing all this minimum/maximum thing, right?


how? me and him basically said the same thing but in different terms lool
Original post by masryboy94
how? me and him basically said the same thing but in different terms lool


yeah i figured, it was just me reading it wrong!
so i'll just remember emf is max when is parallel. and min when perpendicular?
Original post by bobthebuilder
yeah i figured, it was just me reading it wrong!
so i'll just remember emf is max when is parallel. and min when perpendicular?


yepp
Original post by bobthebuilder
omg I am SO confused.
is it just me or do you both contradict each other?

is this very important, because i could've got the answer to that question without knowing all this minimum/maximum thing, right?


If your really having difficulties understanding it, since there's limited time I'd say just at least look at this formula and understand how it works...

emf induced = BANcos(angle)

when coil is perpendicular to magnetic field (or 90 degrees to it)... cos(90)=0
Therefore emf induced = 0

However when it's parallel to the magnetic field (0 degrees to it)...
cos(0) = 1

As you may know this is the maximum value of cos... emf induced is maximum here :smile:
Original post by posthumus
If your really having difficulties understanding it, since there's limited time I'd say just at least look at this formula and understand how it works...

emf induced = BANcos(angle)

when coil is perpendicular to magnetic field (or 90 degrees to it)... cos(90)=0
Therefore emf induced = 0

However when it's parallel to the magnetic field (0 degrees to it)...
cos(0) = 1

As you may know this is the maximum value of cos... emf induced is maximum here :smile:


that really does help to remember it, thank you! :smile:
Hi guys, for the nelsons thornes book on page 58 for summary questions 3ai is the answer in the back of the book wrong?

Because surely you do the change in V from the big mass?

I got 50J, 100J and a 100j

but the answer is 250j, 200j and 200j

help please!
Original post by ladynova
Hi guys, for the nelsons thornes book on page 58 for summary questions 3ai is the answer in the back of the book wrong?

Because surely you do the change in V from the big mass?

I got 50J, 100J and a 100j

but the answer is 250j, 200j and 200j

help please!


i think because they are the equipotentials, at P the gravitational potential is set at 2500kg-1 so that is what it has at that position, it doesn't say the object moved from the body to position P, but rather it says gravitational potential energy straight at P. hope you get that?
I still dont get why the jan 13 paper was SO much harder than all others yet same boundaries.

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