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

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Reply 720

Leechayy

Original post by Chung224

Does anyone agree that there's never been a horrible paper from 2010? Lets just hope they stick to that.

With the way things have been going so far, I doubt it'll stick like that.

OCR are trolls :hmpf:

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Reply 721

Chung224

Original post by Leechayy

With the way things have been going so far, I doubt it'll stick like that.

OCR are trolls :hmpf:

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Hmm donno, with G482 they can ask all sorts of stupid things, it seems in G485 they topics aren't as broad so yeah they'll be hard but i don't think bull****

Reply 722

Leechayy

Original post by Chung224

Hmm donno, with G482 they can ask all sorts of stupid things, it seems in G485 they topics aren't as broad so yeah they'll be hard but i don't think bull****

Truee.

Went through magnetic fields yesterday it's not that bad. My worst stuff left is electromagnetic induction and capacitors stuff. I hate electricity :hmmm:

That and all the essay questions thrown at you are irritating too :redface:

I just don't trust OCR after the FP3 exam I had :colonhash:

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Reply 723

ninjasinpjs

magnetic induction:

is emf generated only by cutting/linking the magnetic field? (can it be generated other ways)

can a long straight wire only cut and not link?

(edited 8 years ago)

Reply 724

Chung224

Original post by Leechayy

Truee.

Went through magnetic fields yesterday it's not that bad. My worst stuff left is electromagnetic induction and capacitors stuff. I hate electricity :hmmm:

That and all the essay questions thrown at you are irritating too :redface:

I just don't trust OCR after the FP3 exam I had :colonhash:

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yeah i recommend you write as much as u can in the written stuff, you never know the mark scheme might be absolute poop, same for you really em induction and fields are my worst.

Reply 725

Chung224

Original post by ninjasinpjs

magnetic induction:

is emf generated only by cutting/linking the magnetic field? (can it be generated other ways)

can a long straight wire only cut and not link?

emf=rate of NBA Area would be constant and so would no of turns (even ratio) so yeah i would think only a varying b field so alternating current or cutting it would induce an emf

Reply 726

ninjasinpjs

Original post by Chung224

emf=rate of NBA Area would be constant and so would no of turns (even ratio) so yeah i would think only a varying b field so alternating current or cutting it would induce an emf

why is it important to know the magnetic flux linkage?

Does it tell us the magnitude of induced emf, and how?

Reply 727

randlemcmurphy

Original post by ninjasinpjs

why is it important to know the magnetic flux linkage?

Does it tell us the magnitude of induced emf, and how?

Faraday's Law states that the magnitude of the induced emf is directly proportional to the rate of change in magnetic flux linkage.

Reply 728

ninjasinpjs

Original post by randlemcmurphy

Faraday's Law states that the magnitude of the induced emf is directly proportional to the rate of change in magnetic flux linkage.

ahhhh, thanks

Reply 729

coder4

Original post by ninjasinpjs

If a electron travels though two plates with a potential difference between them, will the horizontal component of the electron's velocity be effected by the electric field?

Also the electron would travel at right angles to the field so work will be done on the electron but in what direction? ( I think up)

Nah it wont affect the horizontal and the direction is the direction of the field

Reply 730

Jmw123

What's the best way to revise for this exam from now until Thursday? Currently learning the possible long answer questions from this thread: http://www.thestudentroom.co.uk/showthread.php?t=2715379

Reply 731

BecauseFP

Original post by L'Evil Fish

Does anyone know how much of that we need to know? The only time they've ever even hinted at the photocathode and such being relevant was in that crazy 2010 question, every other time it's been sensible stuff about X-ray photons being converted to many visible light photons.

Reply 732

BrokenS0ulz

Original post by BecauseFP

All I've learnt is intensifier screen made of phosphor is placed in front of photographic film. Each x ray photon that hits the phosphor screen is converted into many photons of visible light. This reduces the exposure to x-rays.

Is there anything I've missed?

Reply 733

BecauseFP

Original post by BrokenS0ulz

Honestly, it's weird, the right answer for image intensifier stuff has changed a couple of times, but it generally agreed that the stuff on the 2010 paper I mention is wrong.

Anyway, does anyone know a good way to word the movement of the stuff that's rotating about the patient in a CAT scan? The Jan 2013 mark scheme has this but I've got no idea how to actually write it:
"X-ray beam passes through the patient at different angles / X-ray tube rotates around the patient
A thin fan-shaped beam is used (AW)
Images of ‘slices’ through the patient (in one plane are produced with the help of computer software)
X-ray tube / detectors are moved along (the patient for the next slice through the patient)"
To me it almost seems like it's repeating itself. The best I would have would be "a think fan-shaped beam of X-rays is moved up and down a rotating axial that moves around the patient, these X-rays are then detected by detectors that are also being moved to correspond with the fan-shaped beam of X-rays".

Can anyone word it better?

Reply 734

Jim997

Hi guys, just unsure on how best to answer this question?

Should you say that the temperature of the microwave radiation is 2.7k which corresponds to the tempreture of the universe?

Also , that the cmb is almost perfect uniform, which is significant as these ripples were where matter first started to amass and form what are now galaxies etc.

Then do you talk about it being stretched to microwave spectrum due to the expansion of space? Don't know what the evidence for this is though? Galaxies moving further apart still?

Reply 735

ninjasinpjs

Lenz's law :

Is the opposing force due to the magnetic field created by the current generated?
In other words, the magnetic field initially there and the magnetic field due to the current act against each other which 'causes the oppose to change', is this what lenz's law saying?

Reply 736

Jim997

Also can anyone answer this? 5 marks. Cheers

Reply 737

L'Evil Fish

Original post by Jim997

Also can anyone answer this? 5 marks. Cheers

He said every line of sight should end in a star, and so the sky should be uniformly bright
He assumed the universe was infinite and static
Hubble showed the universe is expanding as there is a red shift, thus the universe can't be infinite
Rate of expansion is limited by speed of light, some lines of sight may not have had enough of time to reach us
Therefore the sky isn't uniformly bright and not light at night

Reply 738

randomuser1

Original post by Jim997

Also can anyone answer this? 5 marks. Cheers

olbers paradox:
assuming universe is static and infinite
sky should be bright in every direction at night
it's not so at least one of these is wrong
hubble stated that universe is expanding (i.e not static) and using his constant we can find the age (therefore not infinite)
This would be the general idea you're trying to convey, although not sure thats in itself 5 marks worth