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

1. (Original post by palacefloor)

For the first question the value of the resistor and time constant depended on the capacitor from the previous graph, so I worked all these out. However when I checked through I looked at the graph and worked out the capacitor to be very slightly different, will I drop any marks for not re-correcting the time constant and resistor or will it be fine?
There will be a range you can have. I had worked it out as 25/3
2. What was the third multiple choice question?
3. (Original post by Jay1421)
The radius of Venus question was worth 3 marks
what was the answer? for the radius and the other dimension we had to find , was it mass or something?
4. for the graph for venus and earth will writing at the start point 9.81 gain a mark on the y axis
5. (Original post by Aethrell)
The distance between then was sqrt(5) so the Force would be 1/5 of the force felt when they were closest together, giving an answer of 5F

(I think)
But the distance between them isn't the hypotenuse. So the distance is sqrt((2r)^2 - r^2) = sqrt(3r^2)
6. (Original post by Jordenwilder1998)
for the graph for venus and earth will writing at the start point 9.81 gain a mark on the y axis
None of us have the mark scheme so no-one here will be able to tell you that.
7. (Original post by palacefloor)

For the first question the value of the resistor and time constant depended on the capacitor from the previous graph, so I worked all these out. However when I checked through I looked at the graph and worked out the capacitor to be very slightly different, will I drop any marks for not re-correcting the time constant and resistor or will it be fine?
What values did you get?
8. (Original post by particlestudent)
Ah right, I think overall it wasn't that bad though (the multiple choice).
Yeah, it was quite nice. My main issue was the electromagnetic brakes question on the written paper. I've never fully gotten my head around electromagnetic induction and I'm currently taking a gap year so I've not had any teachers to ask
9. Do you think credit would be given if I used the count the squares technique to find the area under the graph on question 1?
10. unofficial mark scheme?
11. (Original post by marioman)
None of us have the mark scheme so no-one here will be able to tell you that.
but it said to label the axis so surelyt that will gain some kind of mark considering it was worth 3 marks
12. (Original post by DesignPredator)
Q1 2+3+3+2+1
Q2 2+3+3
Q3 2+4+1+4+1
Q4 1+6+3
Q5 3+3+2

Missing 1 mark can't remember where it was.
The missing mark was for question 3 the first question was actually about the momentum law, when is momentum conserved? I said no external forces acting...
13. (Original post by js.int)
But the distance between them isn't the hypotenuse. So the distance is sqrt((2r)^2 - r^2) = sqrt(3r^2)
For this question, I got 3F, as I concluded using Pythagoras that the side length was root(3)R, then concluded that it would move from root(3)R to 1R so it divides by 1.73, thereby increasing F by (1.73)^2 which is 3
14. Who got +5Q/8 for electric potetial, -4GM/d for gravitaional potential? Work done by 2nC charge as 0.15microC? The one with the charge moving along the electric field line that potential is constant? The one with the electric field strength at the centre of the square = 0? The pendulum one with the biggest amplitude = A? The one with Capacitance decreasing: 96V and 2.9x10^-10 charge?

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15. (Original post by Jay1421)
Yeah, it was quite nice. My main issue was the electromagnetic brakes question on the written paper. I've never fully gotten my head around electromagnetic induction and I'm currently taking a gap year so I've not had any teachers to ask
I struggled to even give an advantage and disadvantage. But my main loss of marks was the momentum one...
16. (Original post by Hattie28)
For the limitation I put dampening due to air resistance? Also on the MC, for the pendulum which one would have the largest amplitude? Overall I found section B okay, but the MC tricky.
I remember my physics teacher saying, when we were doing the EMPA that, that equation is only valid for small angles ( the angle from the equilibrium which it is released )and the MC question was B because it was the same length as the 1st pendulum ( driving force ) therefore frequency is the same and it undergoes resonance.
17. (Original post by Yo12345)
Who got +5Q/8 for electric potetial, -4GM/d for gravitaional potential? Work done by 2nC charge as 0.15microC? The one with the charge moving along the electric field line that potential is constant? The one with the electric field strength at the centre of the square = 0? The pendulum one with the biggest amplitude = A? The one with Capacitance decreasing: 96V and 2.9x10^-10 charge?

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Yep - most of those sound good to me 😃
18. (Original post by js.int)
But the distance between them isn't the hypotenuse. So the distance is sqrt((2r)^2 - r^2) = sqrt(3r^2)
Fair point.

Another one I've messed up...
19. (Original post by DesignPredator)
Here are my answers to Written, the question parts might not be correct.

1ai) 8.26 (will be a range)
ii) 2.6x10^-4

bi)28
ii)5.9x10^4
iii) bottom box ticked

2ai) Derivation
ii) 6.06x10^6 (3SF only)

b) Downward Curve staring at 9.81
Minimum at g=0 at a point slightly offset from halfway closer to Venus
Rises up to 8.87

3a) V=mv/N

b) Derivation

ci) 216
ii) 1.15x10^-19 kgms-1 OR Ns
iii) Anti electron neutrino released also so Beta minus particles have range of Kinetic Energies upon release.

4a) Small amplitude oscillation as only valid for small angular amplitudes.

b) -Set up light string with Bob on the end,
attach top of string to clamp stand boss.
-Measure length from top to centre of Bob.
-Release the Bob so it oscillates with small amplitude.
-Use stop clock to measure time taken for 20 oscillations.
-Divide this by 20 for mean T
-Plot T^2 against L
-Repeat procedure

c) -Student value 4x true value
-Time period half so all values for T^2 will be 1/4 the true
-State equation or show that g is inversely proportional to gradient.

5a) Lenz's Law: Direction of induced EMF/current is always in a direction that opposes the change that caused it.
Faraday's Law: Induced EMF is proportional to rate of change of flux linkage.

b) -Change in flux linkage when current flows.
-EMF induced in wheel (or whatever it was called)
-Current induced in the wheel as good conductor.
-Current carrying conductor (wheel) opposes the field due to coil, therefore there is a force against the direction of motion.

c) Wheel not in contact with electromagnet so no wear, but in brake pads there is wear due to friction.

More energy used or less effective or heating.
Pretty much identical as me
20. (Original post by particlestudent)
I struggled to even give an advantage and disadvantage. But my main loss of marks was the momentum one...
I still can't tell if my momentum one was right, I got around 1 * 10^-19... which didn't seem right.

For the advantage I put that it would be faster because electricity is faster than friction (I don't even know) and then for the disadvantage, I put that to stop a car you'd require a strong electromagnet so that would result in a higher energy use, i.e less efficient? :\

Best of luck!

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