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

Reply 3280

ShutUpLegs

11

Just looked over my paper from last year and damn was I marked harshly! I didn't get one mark on the six marker!

Reply 3281

AR_95

21

What happens in a uniform electric field, when both plates are positive and also when :

1) Both plates have the same PD

2) One plate has a higher positive PD then the other positive PD

And also when both are negative

1) of same PD

2) One plate is more negative then the other

Reply 3282

JJBinn

2

Original post by AR_95

What happens in a uniform electric field, when both plates are positive and also when :

1) Both plates have the same PD

2) One plate has a higher positive PD then the other positive PD

And also when both are negative

1) of same PD

2) One plate is more negative then the other

1) If both plates have the same PD, there is no electric field.
2) There is an electric field in the direction of the higher value PD to the lower value PD. V is the difference between the values.

1) Same as above
2) Same as above, will be in the direction of the least negative to the more negative value.

Anyone feel free to correct me if I'm wrong because I didn't look this up. I think it's correct though :smile:

Reply 3283

EHR223

2

Original post by AR_95

What happens in a uniform electric field, when both plates are positive and also when :

1) Both plates have the same PD

2) One plate has a higher positive PD then the other positive PD

And also when both are negative

1) of same PD

2) One plate is more negative then the other

When one plate has a higher PD than another plate, the direction of the electric field lines go from higher PD -> Lower PD. This is vice versa for two negatively charged plates, but in this instance the electric field lines will go from less negative -> More negative.

When two plates have the same PD, whether it be negative or positive, the net effect of the electric field at a midpoint between them will be zero.

(edited 8 years ago)

Reply 3284

Substitution

3

Great video on resonance

https://www.youtube.com/watch?v=csYUGJLtZnw

Reply 3285

Boop.

12

Original post by JJBinn

1) If both plates have the same PD, there is no electric field.
2) There is an electric field in the direction of the higher value PD to the lower value PD. V is the difference between the values.

1) Same as above
2) Same as above, will be in the direction of the least negative to the more negative value.

Anyone feel free to correct me if I'm wrong because I didn't look this up. I think it's correct though :smile:

Yep, electric field lines are the paths that a small positive charge would follow if placed in the field

Reply 3286

palaseum9

2

Original post by NEWT0N

emf induced is at a pi/2 phase difference between flux linkage. When magnitude of flux linkage is maximum emf induced is 0, and vice versa. The emf induced is maximum when the coil is parallel to the field lines because the coil cuts the flux lines perpendicularly at that instant. Flux linkage is easier to guess intuitively as it becomes maximal when the coil is perpendicular to the field.

Something like this?

Sci_phys_motor_dcmotor_max.png37.5KB

Reply 3287

Kennethm

2

Original post by ShutUpLegs

Just looked over my paper from last year and damn was I marked harshly! I didn't get one mark on the six marker!

I just did the written, you really didn't need to even touch the 6 marker to get an A*.

Sometimes its better to retain or gain marks elsewhere as opposed to spending 10 minutes on 6 marks. The way I see 6 markers are if they are this difficult and demanding then don't bother unless you've done everything else as perfectly as possible and you have the time for it.

Some 6 markers aren't demanding at all and its easy to get 4/5 ish marks from them at first glance which is fine.

Reply 3288

MSB47

2

Original post by huniibehi

Does anybody get how they concluded 38s for this question?

Posted from TSR Mobile

I hate those type of questions. Basically, the pendulum of period 1.9 seconds completes more oscillations within a given time than the pendulum of 2.0 seconds.

One way in calculating the time when they both come back into phase with each other is by having n as the number of oscillations completed by the 2.0 second pendulum... because you know the 1.9 second pendulum will always complete more oscillations than the 2,0 second pendulum you can formulate it...

(n+1)1.9=2.0n

If you re-arrange to find n it should give you n=19, so 2.0 second pendulum completes 19 oscillations before they both come back in phase and if you find the product of the number of oscillations and time period it gives 38 seconds.

Reply 3289

AR_95

21

Why is the energy stored in a capacitor half of that for a battery

Reply 3290

becca9621

Anybody got any predictions?

Reply 3291

gcsestuff

2

Original post by AR_95

Why is the energy stored in a capacitor half of that for a battery

I think it's because it's halved between the plates

Posted from TSR Mobile

Reply 3292

thedon96

1

can someone help with question 23 and 24 of june 11 section A?
https://60abffc9b401b1c0936e01291c15112cab0778c4.googledrive.com/host/0B1ZiqBksUHNYVFI1YlJBOWhwRW8/June%202011%20QP%20-%20Unit%204A%20AQA%20Physics.pdf

Reply 3293

Remiepascua

1

has anybody got any good resources for info on resonance and damping? i have a feeling we'll get some tricky questions on this to catch people out

Reply 3294

xela238

3

Was just wondering, thought it might be a good idea if somone put together a kind of average answer table. For example spring constant usually around the 100s, capacitance usually x10^-6 etc. Would be a great help?

Reply 3295

AR_95

21

Original post by xela238

Was just wondering, thought it might be a good idea if somone put together a kind of average answer table. For example spring constant usually around the 100s, capacitance usually x10^-6 etc. Would be a great help?

I wouldn't advise this, answers and magnitudes can change dependant on different situations

Reply 3296

xela238

3

Original post by AR_95

I wouldn't advise this, answers and magnitudes can change dependant on different situations

But would there not be rough paramteters? so if you got x10^-11 eV not J you know youve gone wrong?

Reply 3297

gabbons

2

Hey guys, can anyone explain why the answer a parabola in the vertical plane? I thought it would be in the horizontal

Reply 3298

Kennethm

2

Original post by thedon96

can someone help with question 23 and 24 of june 11 section A?
https://60abffc9b401b1c0936e01291c15112cab0778c4.googledrive.com/host/0B1ZiqBksUHNYVFI1YlJBOWhwRW8/June%202011%20QP%20-%20Unit%204A%20AQA%20Physics.pdf

23 - the magnet and coil are in relative motion with each other so the coil is cutting the magnetic flux lines of the magnet therefore inducing an emf in the surrounding area which will show a reading in the ammeter as there is a current in the coil.

(you do not need to consider lenz's law here at all so don't confuse yourself with that)

24 -

ε = BANωSinωt

just apply your knowledge of maths graphs and the information they gave you to this equation.