georgespack
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#841
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#841
(Original post by Lucy-1995)
Its do with 4-stroke engines the power stroke occurring every other cycle I think. Although I went to my teacher and she was baffled aswell, but she checked on the teachers notes for the applied topic and it explained it I just can't remember exactly haha.
Yeah the crankshaft turns twice per cycle of the engine, if you think about it the piston goes up and down twice every cycle
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jqian
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#842
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#842
(Original post by The H)
Anyone doing Turning points
What do you think for a potential 6 marker? All 3 that have been so far were in the topic of wave-particle duality, so maybe some special relativity or discovery of electron?
I'm doing turning points.

Personally, I don't mind the wave-particle 6 markers. I would struggle to write 6 marks on the Michelson Morley experiment but if a 6 marker is on discovery of the electron I would imagine we would have to describe at least 2 experiments since I think a single experiment in that chapter is too simple to describe.

The June 12 paper was quite horrible, hopefully we get a nicer paper.
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The H
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#843
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#843
(Original post by jqian)
I'm doing turning points.

Personally, I don't mind the wave-particle 6 markers. I would struggle to write 6 marks on the Michelson Morley experiment but if a 6 marker is on discovery of the electron I would imagine we would have to describe at least 2 experiments since I think a single experiment in that chapter is too simple to describe.

The June 12 paper was quite horrible, hopefully we get a nicer paper.
I didn't think the June 12 paper was that bad for TP, but i thought it was very hard for nuclear and thermal
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Jack93o
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#844
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#844
thats alright then, I was wondering if I'm the only one who's confused by this
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kabutsu12
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#845
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#845
(Original post by Lucy-1995)
Its do with 4-stroke engines the power stroke occurring every other cycle I think. Although I went to my teacher and she was baffled aswell, but she checked on the teachers notes for the applied topic and it explained it I just can't remember exactly haha.
Cheers
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kingm
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#846
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#846
Does anyone know if we need to know feynam diagrams for this exam?
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Jack93o
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#847
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#847
does anyone understand the safety aspect to radioactive tracers being used in patients?

apparently they need to have a short half life so that the radioactive substance decays quickly and doesn't stick around inside the patient

but, if it has a short half life, then that just means that the ionization (energy released) produced over a shorter period of time, right?

wouldn't the patient still get exposed to the same amount of ionization? it seems to me like its just a matter of whether its done over a shorter or longer period of time....
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JayJay95
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#848
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#848
(Original post by Jack93o)
That makes sense, but some nucleus just decay due to having excess neutrons, rather than as a result of having just absorbed a neutron

i.e., they've had these neutrons for a long time, its not like they've just suddenly become unstable as a result of the energy released from absorbing a neutron

how do you explain beta minus decay? (where the neutron changes into a proton, this isn't fission, right?)
The nucleus of neutron rich nuclei are unstable. Its due to the fact the neutron to proton ratio isnt quite right, I guess its to do with something beyond A level that we dont need to know for the exam. However its energetically favourable for that nucleus to decay via beta radiation as it reduces the neutron to proton ratio and increases its stability.

I guess if you look at the binding energy per nucleon curve you can see that iron is the most stable element so ideally thats the position to be in

Hope that helps

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bugsuper
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#849
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#849
(Original post by Jack93o)
does anyone understand the safety aspect to radioactive tracers being used in patients?

apparently they need to have a short half life so that the radioactive substance decays quickly and doesn't stick around inside the patient

but, if it has a short half life, then that just means that the ionization (energy released) produced over a shorter period of time, right?

wouldn't the patient still get exposed to the same amount of ionization? it seems to me like its just a matter of whether its done over a shorter or longer period of time....
I wasn't sure about this, but think of it this way

A short half-life means a high activity. Let's say there's a minimum activity that a source needs to have to be detectable outside the body, or to be used for imaging. Now, there are two ways of getting the necessary activity - one is to have a small amount of a substance with a short half-life, and the other is to have a large amount of a substance with a big half-life. If you had the same amounts of each substance, then yes, I agree, the total radiation absorbed by the patient would be the same. But if you have a substance with a long half-life, you'd need to put more of it into the patient for its radiation to be detected outside the body

this isn't in the textbook or anything but it's how I always reasoned it
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bugsuper
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#850
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#850
(Original post by kingm)
Does anyone know if we need to know feynam diagrams for this exam?
I'm pretty sure there's a synoptic element to this exam, so it's probably worth looking them over just in case
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Jack93o
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#851
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#851
(Original post by bugsuper)
I wasn't sure about this, but think of it this way

A short half-life means a high activity. Let's say there's a minimum activity that a source needs to have to be detectable outside the body, or to be used for imaging. Now, there are two ways of getting the necessary activity - one is to have a small amount of a substance with a short half-life, and the other is to have a large amount of a substance with a big half-life. If you had the same amounts of each substance, then yes, I agree, the total radiation absorbed by the patient would be the same. But if you have a substance with a long half-life, you'd need to put more of it into the patient for its radiation to be detected outside the body

this isn't in the textbook or anything but it's how I always reasoned it
oh thats makes sense now, thanks
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Jack93o
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#852
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#852
(Original post by JayJay95)
The nucleus of neutron rich nuclei are unstable. Its due to the fact the neutron to proton ratio isnt quite right, I guess its to do with something beyond A level that we dont need to know for the exam. However its energetically favourable for that nucleus to decay via beta radiation as it reduces the neutron to proton ratio and increases its stability.

I guess if you look at the binding energy per nucleon curve you can see that iron is the most stable element so ideally thats the position to be in

Hope that helps

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good to know that we don't need to know it for the exam
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franko06
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#853
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#853
Spent so much time on astrophysics I'm forgetting everything on section A

STRESSED


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ehtisham_1
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#854
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#854
(Original post by franko06)
Spent so much time on astrophysics I'm forgetting everything on section A

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Same here
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kingm
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#855
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#855
Has anyone done Q 2.a on the specimen paper?

"There is 3.5 × 10-4 m3 of air space in the bottle and the volume of the pump chamber changes from zero at the beginning of the up-stroke to 6.5 × 10-5 m3 at the end of the up-stroke. The initial pressure of the air in the bottle is that of the atmosphere with a value of 99 kPa.
Assuming the process is at constant temperature, calculate the pressure in the bottle after one up-stroke of the pump."

I did it and got p = 5.3 x 10^5.

They started using some crazy number in the mark scheme and wanted to know if it was a mistake by me or them!?
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kingm
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#856
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#856
geez man, even part B to that question includes typos...
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ehtisham_1
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#857
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#857
Hey guys can someone help me with question 4 on topic 12.1 in the the nelson thrones book.

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Pinkhead
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#858
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#858
(Original post by kingm)
Has anyone done Q 2.a on the specimen paper?

"There is 3.5 × 10-4 m3 of air space in the bottle and the volume of the pump chamber changes from zero at the beginning of the up-stroke to 6.5 × 10-5 m3 at the end of the up-stroke. The initial pressure of the air in the bottle is that of the atmosphere with a value of 99 kPa.
Assuming the process is at constant temperature, calculate the pressure in the bottle after one up-stroke of the pump."

I did it and got p = 5.3 x 10^5.

They started using some crazy number in the mark scheme and wanted to know if it was a mistake by me or them!?
p1v1=p2v2

p1=99000, v1 = 3.5x10^-4
v2= v1+ 6.5x10^-5
should get something like 83Kpa
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bobthebuilder
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#859
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#859
how do i get the formula sin theta = 1.22 lambda/ distance using the formula sheet? or do i have to remember it?
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kingm
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#860
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#860
(Original post by Pinkhead)
p1v1=p2v2

p1=99000, v1 = 3.5x10^-4
v2= v1+ 6.5x10^-5
should get something like 83Kpa
Ah i see. You're adding the two volumes for v2. Cheers.
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