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AQA Physics PHYA4 - 20th June 2016 [Exam Discussion Thread]

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Original post by particlestudent
Again this is confusing me... The induced EMF is greatest when it's 90degrees to give sin90=1, making the emf induced a maximum and so the rate of change of flux linkage a maximum....

This is starting to **** me off now


yes
Reply 1021
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Original post by particlestudent
Again this is confusing me... The induced EMF is greatest when it's 90degrees to give sin90=1, making the emf induced a maximum and so the rate of change of flux linkage a maximum....

This is starting to **** me off now


This angle is the angle between the normal to the plane of the coil.... I get why it's annoying :redface:

but the rate of change of flux is greatest when the coil is parallel to the field, just look at the graph of flux linkage of a rotating coil and look at where the gradient is greatest
Original post by particlestudent
Again this is confusing me... The induced EMF is greatest when it's 90degrees to give sin90=1, making the emf induced a maximum and so the rate of change of flux linkage a maximum....

This is starting to **** me off now


I think it ****s most people off :lol:

Hopefully the question will be based on a graph, and you can use the gradient (flux/time).
Original post by ombtom
I've lost your original question now but I'm sure it gave the volume per second. :tongue:


Original post by abro1089
the volume is given in the question. it gives in m^3 per second and you model it as one second, so it is essentially the volume of the cylinder!


Original post by d14m
the volume leaving the hose per second times by density = mass leaving hose per second

the momentum per second is just mass per second x velocity of the water


Well thank you everybody I finally got it!

Took three people to knock it through my thick skull haha :biggrin: definitely need some sleep....
Do we need fleming's right hand rule
help me i'm going to fail
Original post by doshea1311
yes


hi
Original post by abro1089
hi


hi
Original post by d14m
This angle is the angle between the normal to the plane of the coil.... I get why it's annoying :redface:

but the rate of change of flux is greatest when the coil is parallel to the field, just look at the graph of flux linkage of a rotating coil and look at where the gradient is greatest


Okay thanks. I'm off to sleep now, need it!
Original post by ombtom
Was just about to ask this. I'm going to guess something about magnetic fields. Hopefully not damping/natural frequencies or an experiment (do they still do that in unit 4?) :colondollar:


Really hope not! I can't recall a particular experiement I've had to learn (nothing like measuring internal resistance or young's modulus from AS anyway).

I'm hoping and praying electromagnetic induction isn't anything in the 6 marker - unless it's how a transformer works.
Original post by beggelton
Do we need fleming's right hand rule
help me i'm going to fail


yeah you do, you can use it for eddy currents which may come up
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Original post by beggelton
Do we need fleming's right hand rule
help me i'm going to fail


Flehming's Right hand rule is for generator situations, ie where a coil is rotating through a magnetic field (kinetic energy --> electric potential)
Which angle to we take when using the BANcos(theta) formula, is it from the coil to the lines or from the coil to the perpendicular of the lines????
I've done every past paper and I've used the equation to find the average induced eng from a rotating coil a grand total of 0 times. Wtf,
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d14m
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Can we list potential 6 markers? I hate this question
Aqa PhysA: https://gyazo.com/f7d3d3d1689a6b4fd79d7c8eadd1dfc1
You don't need to know it

still going to fail
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Original post by Questioner1234
Which angle to we take when using the BANcos(theta) formula, is it from the coil to the lines or from the coil to the perpendicular of the lines????


It is angle between the field lines and the normal to the coil
Original post by beggelton
Do we need fleming's right hand rule
help me i'm going to fail


It's unlikely to come up but I think it's still in the specification.

This is how I remember them:

Left hand: current causes movement.

Right hand: movement causes current.

Right hand grip rule for current through wire and direction of magnetic field around the wire.
Original post by lucabrasi98
I've done every past paper and I've used the equation to find the average induced eng from a rotating coil a grand total of 0 times. Wtf,


You must've missed a question. I'm sure I did that this morning.
This is ****ed mates. What're the theories on the six marker, haven't been keeping up to date
Original post by ombtom
You must've missed a question. I'm sure I did that this morning.


Average induced emf is just max emf/root2 isn't it?

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