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WJEC A2 PH5 Exam 18th June

Hey, just wondering if anyone wants to discuss the exam tomorrow on what will likely come up in both the core exam and the case study.

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Reply 1

math42

Case study there'll probably be a lot of equation checking/number crunching and some deriving of certain equations.
Nuclear I'd expect the usual stuff...they hardly seem to change. They might ask for uses of radioisotopes. Also a rotating coil explain question might be asked for. Linear accelerator for B-fields maybe? Whichever way, I'm not looking forward to this..

Reply 2

JakeDaw

Original post by 1 8 13 20 42

Would you be able to outline the basic information we need to know about the different types of particle accelerators and how they work please?

Reply 3

math42

Original post by JakeDaw

Would you be able to outline the basic information we need to know about the different types of particle accelerators and how they work please?

The book claims you don't "need" to know anything but it helps

The fundamental particle accelerator doesn't have much to it...an electric field is generated between the anode and the cathode and this accelerates the electron.

(note that I'll keep referring to "the electron" but you could have a proton or alpha or whatever..so in place of where I say "e", you'd need 2e for an alpha for instance)

Then there's the first alternating pd one. (thing it's called linear accelerator?) Essentially the electron is first attracted to a tube of positive PD, then as it goes through said tube the PD turns negative and it is accelerated out, then the next tube turns positive and so on... the AC frequency is not altered while the gap between tubes and their size must be increased in order to account for the acceleration

The cyclotron is another one with constant frequency (and B field); this is the first one where you'd need to compare Bve to mv^2/r (or use omega if frequency is asked for); essentially the cyclotron has the electron spiralling out in circles, as the electron is being accelerated the radius of its path must increase.
This is because if you simply that expression you have Be = mv/r Be is constant so v/r is constant

The synchrotron is another circular one and perhaps the nastiest; the AC voltage frequency and the B field are constantly changing because the particle moves in a circle of sustained radius. The electron is accelerated in a somewhat similar way to the linear accelerator, it goes through 4 tubes per cycle such that the voltage alternates fully twice (so circular motion frequency is half the AC frequency: important to remember). The B field increases in order that, as before Be = mv/r can be constant (since v is increasing but m/r and e are constants)

Reply 4

JakeDaw

Original post by 1 8 13 20 42

Wow thank you so much for that, you really typed a lot and it makes such a difference for my exam tomorrow! Physics is the one exam I'm a bit unsure about reaching my conditional offer for (even if I am a bit more secure in PH5 than PH4). I hope the exam goes well for you tomorrow.

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Reply 5

math42

Original post by JakeDaw

No problem, allowed me to consolidate too. :tongue:

I hope it goes well for you too; I'm not holding too much hope for myself mainly due to Sections B and C (doing option A and they can't be bothered to explain fully in the text book :angry:

)
I guess nothing can be much worse than my PH4 though..

Reply 6

gilbertblythe

If they ask us to derive equations, would most things be on the data sheet or are there ones we should remember? Really worried about the case study, not sure what to expect :s-smilie:

Reply 7

wb25

Can someone explain to me how conservation of energy applies to the rocket in the case study ? Thanks for the help!

Reply 8

math42

Original post by gilbertblythe

If they ask us to derive equations, would most things be on the data sheet or are there ones we should remember? Really worried about the case study, not sure what to expect :s-smilie:

Well most of the equations from which you derive are on the data sheet, but in general derived equations are not. (and neither is E = V/d, perhaps because it's implicit in the electric fields equations) The case study questions tend to be in part synoptic understanding (like this one brings together SUVAT, logs, thermodynamics..), in part just carefully copying (but not quoting) the text and in part using the many equations.

Original post by wb25

Can someone explain to me how conservation of energy applies to the rocket in the case study ? Thanks for the help!

I think until they take gravity into account rather late on, the expelled water is doing work compressing the gas, hence the rocket moves up. The energy considerations are implicit in equation 5, I think (multiply everything by the volume). We later have it a bit more complicated, the gain in gph and the work done against air resistance compete with the work done on the gas and kinetic energy.

edit: I don't have a great understanding of the case study to be honest (and I can kind of imagine how the water "pushes" up against the gas but it feels weird to say it's compressing it when the pressure is actually going down)

If anyone reads this probably best to completely ignore the rocket part, I haven't a clue

(edited 8 years ago)

Reply 9

JakeDaw

Original post by wb25

Can someone explain to me how conservation of energy applies to the rocket in the case study ? Thanks for the help!

So the idea of course is that energy at the start of the system = energy at the end of the system. At the start you do work on the gas compressing it, storing the energy and potential energy. The idea is then that all of this stored energy is transferred into kinetic energy of firstly the water and as a result kinetic energy of the rocket. The very first equation then assumes that the all of the stored energy is fully converted to kinetic energy of the rocket (except it isn't because most is given to the water), and then all of the kinetic energy of the rocket is converted to gravitational potential energy (except it isn't because work is done on the air to move it out the way - air resistance).

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Reply 10

wb25

How did it go ?

It was so different to all the past papers I'm not sure how I did to be honest!

Reply 11

AGB

Did anyone else find that abit strange??? ........

Reply 12

Wiggledinho

Original post by wb25

How did it go ?

It was so different to all the past papers I'm not sure how I did to be honest!

most people I spoke to found it hard including people people with Oxbridge offers. I found the AC option really difficult tbh

Reply 13

troubadour.

I couldn't finish it. :/ So many gainable marks lost...

(edited 8 years ago)

Reply 14

JakeDaw

I managed to finish it all but left out the last question on the cyclotron because I couldn't figure out how to work the velocity out. I now realise it was an energy problem but I'm not to worried about it. It was very different to past papers so I'm hoping the grade boundaries will reflect that. Luckily though the medical physics option was a breeze

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Reply 15

JakeDaw

I also thought the case study wasn't that bad actually as well. Could've been a lot worse

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Reply 16

wehttam123

I thought it was hard to begin with but found it ok after I went back over stuff. I didn't like the first question on capacitors at all though. My option (energy matters) could hardly have been any easier however! I thought the case study questions were quite easy this time. What did everyone else think about the case study?