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# G495 - Field and Particle Pictures: June 11th Tweet

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1. Re: G495 - Field and Particle Pictures: June 11th
(Original post by xiyangliu)
permeability is a property of a material therefore it can't change.. But permeance of the core depends on cross sectional area therefore a crack A has decreased therefore I agreed.. As A is proportional to the permeance ...

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i said i disagreed because permeability is a property of the material and it cannot change...the magnetic circuit is not compromised only of iron because an air gap has been introduced...therefore working out the permeability from the new permeance would not give the permeability of the iron (you can only apply that equation to a material if the magnetic circuit is compromised solely of that material with no air gaps)
2. Re: G495 - Field and Particle Pictures: June 11th
I feel like this test went well. for the agree/ disagree with the boy I kinda put 2 different things - that the cross sec area changed and the permativity of the system changed..

Can someone post the unofficial mark scheme / paper??
3. Re: G495 - Field and Particle Pictures: June 11th
(Original post by PhysicsGirl)
I can't remember too much either, especially not the correct question numbers but I think a few of the wordier section A questions answers were;
1) C
2) a) neutron
b) neutron
3. Was this the proton question? If so, field strength = 0 because field strength = force per unit charge, forces cancel therefore field strength = 0
and potential doubles because you've added another potential 'hill' on the other side
4) choosing the correct region of the graph? -A
5) number remaining in the decay question? As Oromis said, it was 55% :-)
And I think that's all I remember for section A
9) a) Question went something like this: Explain why the electron travels in a curved path. Mention the varying force; you may add arrows to the diagram if you want. My answer: I annotated the diagram, said the force from the nucleus was negligible in the straight bits, and drew arrows on the curved bit perpendicular. Then wrote a waffly explanation using f=kqQ/r^2, talked about the force increasing as r decreased, mentioned parabolic nature of path. Probably not the most efficient way, but I went for trying to cover everything.
Was this the one with the graph on it and you had to use the n=1.2 for the minima, work out the de Broglie wavelength and then use that to calculate an energy? Or something like that?
10) This was the permeability question, I think? First wordy bit was talking about what would happen to the flux (I think it was flux?) when the core cracked and created an air gap (air = significantly lower permeance, therefore reduces the total permeance of circuit, therefore flux is reduced by the equation: flux= permeance * current-turns). Then asked to discuss whether the opinion that the permeability of iron had changed because the permeance of the circuit had fallen. (no- permeability of iron is fixed (material property), formula is still correct but the magnetic circuit is no longer made entirely from iron, therefore permeance no longer follows that relationship)
11) This might have been the proton beam question. Work out a risk, then the state and explain for what penetration the proton beam was most effective, then use the graph to explain why the number gained in part b) was a minimum.
12) This was the grain between the vertical plates question, I think. You had to draw five field lines (I went for five, horizontal, parallel, equally spaced, lines running from positive to negative but I'm not entirely sure they had to be equally spaced?) and then a 24kV equipotential line (vertical line down centre, perpendicular to field lines) and then the other wordy bit was saying what would happen to the horizontal distance moved by the grain if the separation of the plates was doubled and why (distance halved because force halved because E halved because d doubled?)
And then onto section C (which was a behemoth of a section in terms of numbers of questions, I thought)
13) Explain how brittle fracture occurs. I waffled about crack propagation and drew a diagram showing how stress is concentrated at the point?
14) a) Show that a wave would take less than four hours to go round the earth (convert wave speed into km per hr, work out circumference from the radius given, divide circumference by speed, comes out something like 3.7hours?)
b) show the two wavelengths were equal (both 6 km)
15) can't remember
17) work out that you need a length of about 100 (I got greater than 99) for the frequency you want
18) accelerating force question that was weird, threw me off a bit because it said explain why the accelerating force was small, and I could say why the acceleration was small, but this didn't necessarily make the force small, so yeah. Bit confused
19) Not sure what question this was?
20) Last bit was wordy, talking about damping, restoring forces, creation of eddy currents in opposition to direction of movement due to Lenz's law etc

And I think that's all I remember. Hope that helps :-)
OK, in the absence of a scan, I really want to try to write down a copy of the paper. Oromis, it might just have been a list of numbers, but it's been really helpful!

One of the Section A answers was 0.22m, which was "Show the radius of this particle's path is about 0.2m given its momentum etc." This might have been included in Q9, though.

Q8 was just a straight out "Here's a wire, with this length, and this current, in a field of this strength, find the force". 0.014N sounds fairly familiar from Oromis.

The other Sect A question anyone?

The order for section B - I think it was Q9 electron bending around nucleus; Q10 proton beam; Q11 grain between electric plates; Q12 permeability. Not that it matters XD

Q15 asked "Explain why long. + transverse waves can cause vibrations in all three planes." I had to come back to it - I ended up saying that longitudinal waves cause vibrations in one plane and transverse waves in the other two, then drew some really bad diagrams of the oscillation of all three waves.... Would like to know some other people's takes on this.

I think your Q17 and 18 might have been two parts of Q17.
Q17 - the restoring force in an oscillation is mg sin(a), where a is the angle the pendulum makes with the vertical. But if the length is 100m and the displacement is a few mm, then a will be tiny.

Q18 might have been the Richter Scale question (compare the shaking amplitudes and energy). I had a very strong urge to highlight the first sentence of this question which simply read "In an earthquake, the ground shakes." and write "O RLY"

Q19 started with finding the flux linkage of the coil in two parts. Then there were 4 marks for finding the emf induced (wasn't this an average emf? Surprised they didn't ask us to 'state any assumptions made'...) when the flux linkage was halved.
4. Re: G495 - Field and Particle Pictures: June 11th
(Original post by tomp99)
OK, in the absence of a scan, I really want to try to write down a copy of the paper. Oromis, it might just have been a list of numbers, but it's been really helpful!

One of the Section A answers was 0.22m, which was "Show the radius of this particle's path is about 0.2m given its momentum etc." This might have been included in Q9, though.

Q8 was just a straight out "Here's a wire, with this length, and this current, in a field of this strength, find the force". 0.014N sounds fairly familiar from Oromis.

The other Sect A question anyone?

The order for section B - I think it was Q9 electron bending around nucleus; Q10 proton beam; Q11 grain between electric plates; Q12 permeability. Not that it matters XD

Q15 asked "Explain why long. + transverse waves can cause vibrations in all three planes." I had to come back to it - I ended up saying that longitudinal waves cause vibrations in one plane and transverse waves in the other two, then drew some really bad diagrams of the oscillation of all three waves.... Would like to know some other people's takes on this.

I think your Q17 and 18 might have been two parts of Q17.
Q17 - the restoring force in an oscillation is mg sin(a), where a is the angle the pendulum makes with the vertical. But if the length is 100m and the displacement is a few mm, then a will be tiny.

Q18 might have been the Richter Scale question (compare the shaking amplitudes and energy). I had a very strong urge to highlight the first sentence of this question which simply read "In an earthquake, the ground shakes." and write "O RLY"

Q19 started with finding the flux linkage of the coil in two parts. Then there were 4 marks for finding the emf induced (wasn't this an average emf? Surprised they didn't ask us to 'state any assumptions made'...) when the flux linkage was halved.
Yeah, I thought I'd gotten my order all jumbled up.
For question 15, I drew a diagram the looked like an x,y,z graph with arrows, indicated that the direction of travel was along my z axis, and then wrote an explanation beside explaining that transverse waves vibrate perpendicular to (x and y on my diagram) and longitudinal waves vibrate in the direction of travel (z on my diagram) hence it was possible to have vibrations in all three spatial directions. Which sounds pretty similar to what you did :-)
5. Re: G495 - Field and Particle Pictures: June 11th
(Original post by Cmann)
thanks! i done 26/30.1=0.86378 then 0.5^(0.86378)*100=55%.... thats correct right?
i did something completely different:P
worked out lambda using the half life, and then let N(0)= 100
N=100e^-labda * 26
which gave me roughly 55. its right, but i wonder if i'll get the marks for it
Last edited by Dhanu123; 12-06-2012 at 11:47.
6. Re: G495 - Field and Particle Pictures: June 11th
(Original post by PhysicsGirl)
For question 15, I drew a diagram the looked like an x,y,z graph with arrows, indicated that the direction of travel was along my z axis, and then wrote an explanation beside explaining that transverse waves vibrate perpendicular to (x and y on my diagram) and longitudinal waves vibrate in the direction of travel (z on my diagram) hence it was possible to have vibrations in all three spatial directions. Which sounds pretty similar to what you did :-)
This sounds like a really good explanation actually! But yeah, similar ideas.
7. Re: G495 - Field and Particle Pictures: June 11th
(Original post by Dhanu123)
i did something completely different:P
worked out lambda using the half life, and then let N(0)= 100
N=100e^-labda * 26
which gave me roughly 55. its right, but i wonder if i'll get the marks for it

That is how I did it. I wouldn't know how else to do it tbh.

anyway,

1b) was something like work out the current, I think I got 0.9A.

Section B
1) Explain the forces on the particle for it to deflect.

Force on the particle initially is only due to its velocity; so it goes straight through.
When it deflects, the force due to velocity is perpendicular to the force due to the magnetic field; so it follows a curved trajectory.

This question seems to have brought up some debate. Check this: http://hyperphysics.phy-astr.gsu.edu...ic/movchg.html. Or this even: http://hyperphysics.phy-astr.gsu.edu...maspec.html#c2

Section C
1) they were both 6km
x) Why does movement generate emf? Emf is the rate of change of flux linkage; change in flux linkage caused by the movement of the seismometer generated emf.
Last edited by EricEdwardSelvaraj; 12-06-2012 at 13:15.
8. The only thing that I worry abt this exam is my terrible hand writing ...

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9. Re: G495 - Field and Particle Pictures: June 11th
hey,
has anyone got the paper, just i cant get it a college, so was hoping someone to help me out

thanks
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