OCR Physics A G485 - Frontiers of Physics - 18th June 2015 Watch

nothepreacher
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#641
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(Original post by L'Evil Fish)
Textbook questions look like utter ****e lol

I've never ever done them for anything

They're like unrelated
They are quite tricky haha glad you smart lot agree, it is a relief for me haha but I am doing them tomorrow, hopefully my dad will help. I guess I have less pressure for this exam cause I am already in uni
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rachelc142
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(Original post by L'Evil Fish)
Textbook questions look like utter ****e lol

I've never ever done them for anything

They're like unrelated
I feel like they're slightly better for 485 than for 484
some of the mech stuff was stupid so I avoided them
I'm just going over my notes atm
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Leechayy
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(Original post by nothepreacher)
Well they aren't questions but I just do nt understand the concept very well, i do not understand the explanation in the book very well. You don't need to know it in great detail but I you do need to make reference to it when explaining MRI.
Ohhhh I know what you're talking about now but I can't really remember:mmm:
Type in OCR A Physics G485 concise notes and click on the pdf by mathsmadeeasy.

It explains everything for you in the whole unit in less than 10 pages

Posted from TSR Mobile
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jcwh97
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(Original post by Zoze)
Can someone please explain to me the evolution of the sun? The cambridge book explanation is confusing and I feel it's wrong? Every source I've looked at says that the fusion of protons in the hydrogen shell causes the expansion. :s for example http://www.astro.cornell.edu/academi...1/evol_sun.htm and wikapedia and lots of other sources
Hydrogen fusion in the core decreases as the core mainly consists of fusion products such as helium nuclei. Hence the core will collapse due to the radiation pressure decreasing. The loss of GPE and gain in KE further increases temperature and the pressure of the core.The increase in pressure of the core causes the Sun to expand, becoming a red giant. At temeperatures of 10^8K, helium nuclei will fuse at a phenomenal rate and when this fusion comes to an end, the Sun will become unstable and will radiate most of its mass outwards in huge ion sprays. The rest of the mass and the core will shrink, forming a white dwarf.
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sagar448
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Can someone please tell me what you would say for this...

Compare and contrast decay of radioactive nuclei and decay of charge on a capacitor a C-R circuit

It's straight out of the specification.

thanks.
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Elcor
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#646
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Apparently the spontaneous nature of radioactive decay means the decay can't be induced, but why doesn't fission count as induced? Is it because when a thermal neutron collides with an unstable nucleus you're actually making it a very unstable isotope for a split second, so that doesn't count as inducing the decay?
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Elcor
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(Original post by sagar448)
Can someone please tell me what you would say for this...

Compare and contrast decay of radioactive nuclei and decay of charge on a capacitor a C-R circuit

It's straight out of the specification.

thanks.
Both are exponential
Rate of charge decay depends on C and R
Rate of radioactive decay depends on the decay constant
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sagar448
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(Original post by Elcor)
Both are exponential
Rate of charge decay depends on C and R
Rate of radioactive decay depends on the decay constant
Thanks
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hol31
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Can anyone explain electromagnetic induction for me? I wouldnt know where to begin explaining it. Especially with regard to emf induced in a coil.

Thanks
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coder4
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(Original post by rachelc142)
I feel like they're slightly better for 485 than for 484
some of the mech stuff was stupid so I avoided them
I'm just going over my notes atm
Which textbook do you use? theres 2 out for physics, the one i have this year is pretty good
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boristeve
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(Original post by hol31)
Can anyone explain electromagnetic induction for me? I wouldnt know where to begin explaining it. Especially with regard to emf induced in a coil.

Thanks
in what context? A transformer?

if so, in a transformer an AC is passed through the primary coil of the transformer. This changing emf in the PC produces a constantly changing magnetic flux. (since a magnetic flux is produced when there is a change in the emf, using DC would produce flux when it is switched on, as that is a change in emf, but then the flux would dissapaer since the emf is not changing. so transformers do not work with DC.)

The iron core of the transformer causes a flux linkage between the two coils, and that means a changing magnetic flux is produced in the secondary coil. Due to faradays law, this changing flux induces an emf in the secondary coil, and the emf is proportional to the number of turns on each coil.
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boristeve
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(Original post by Elcor)
Apparently the spontaneous nature of radioactive decay means the decay can't be induced, but why doesn't fission count as induced? Is it because when a thermal neutron collides with an unstable nucleus you're actually making it a very unstable isotope for a split second, so that doesn't count as inducing the decay?
No, when the neutron is absorbed by a heavy nucleus, it excites it with it's kinetic energy, the nuclei splits into two daughter nuclei and emits more neutrons. The reason this isn't decay is because i think it is not exponential and has nothing to do with the decay constant. I also (though i could be wrong) don't think there is a weak force interaction involved with nuclear fission, whereas there is in other kinds of radioactive decay
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Tiwa
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(Original post by rachelc142)
any nice revision suggestions/sources? I think I've exhausted past papers
Some revision notes and some extra past papers in this link. http://www.st-ambrosecollege.org.uk/...sics-a2-level/
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sagar448
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When a capacitor is charging or discharging through a resistor then the voltage across the capacitor relative to time should be a curve up or curve down since it's exponential.
The question in January 2013 1ii2 says it's a straight line through the origin? Please help?
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L'Evil Fish
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(Original post by sagar448)
When a capacitor is charging or discharging through a resistor then the voltage across the capacitor relative to time should be a curve up or curve down since it's exponential.
The question in January 2013 1ii2 says it's a straight line through the origin? Please help?
I just did that one, lost a mark there... Not sure why
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boristeve
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(Original post by sagar448)
When a capacitor is charging or discharging through a resistor then the voltage across the capacitor relative to time should be a curve up or curve down since it's exponential.
The question in January 2013 1ii2 says it's a straight line through the origin? Please help?
the key is it says current is constant 40 microamp. since

Q = CV

It = CV

V = It/C

I and C are constants

V = kt

there fore a straight line through the origin
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Oraeng
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On Jan 13 6)c)i) there's a question about calculating intensity using I=Ioe^μx
Why don't you have to convert the units of x and μ from cm to m if the initial intensity is given in Wm^-2 and the final intensity is in Wm^-2?
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L'Evil Fish
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(Original post by Oraeng)
On Jan 13 6)c)i) there's a question about calculating intensity using the I=Ioe^μx
Why don't you have to convert the units of x and μ from cm to m if the initial intensity is given in Wm^-2 and the final intensity is in Wm^-2?
Because mu and x cancel out the units
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sagar448
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(Original post by boristeve)
the key is it says current is constant 40 microamp. since

Q = CV

It = CV

V = It/C

I and C are constants

V = kt

there fore a straight line through the origin
Oh I see, but then when would it be exponential?
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Oraeng
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(Original post by L'Evil Fish)
Because mu and x cancel out the units
So why is it wrong if you do convert them if the units cancel out anyway?
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