June 2011 G485-Fields, Particles and Frontiers of Physics Watch

Captain Hob
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#641
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#641
(Original post by Pandit Bandit)
describe and interpret Hubble’s redshift
observations and what he deduced from it?
Hubble measured the redshift values of distant galaxies and drew a graph of apparent speed against the distance to the galaxy. His graph was a straight line through the origin, indicating that apparent velocity of recession is proportional to the distance to the galaxy. That's where we get Hubble's constant.
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M_I
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#642
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#642
(Original post by anshul95)
well actually that is an incorrect definition of the photoelectric effect as applied to X-rays. Don't worry I know the CGP book says this, but the extra energy of the photon (which of course has to above the work function) becomes the energy of the electron. http://www.upscale.utoronto.ca/PVB/H...yInteract.html
You are explaining the characteristic wavelengths which occur when the electrons hit the tungsten target (this is not the photoelectric effect as it does not release an electron but an x-ray photon).
Oh yeah, lol, your right
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Oh my Ms. Coffey
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#643
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#643
Gamma cam/Endoscope/MRI would be amazing to get, I still think it will be nuclear power plant.
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Lengalicious
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#644
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(Original post by Pandit Bandit)
describe and interpret Hubble’s redshift
observations and what he deduced from it?
as objects emitting EM radiation receed from the observer the wavelengths of the signals increase as the frequency decreases causing the line spectra to be shifted towards the red end of the spectrum.
It can be deduced that due to the recessional nature of galaxies and stars that at some point they must have been closer together which coincides with the big bang theory.
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muffingg
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#645
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#645
(Original post by Lengalicious)
judging by what didnt come up in the last 2011 jan paper, im guessing there will be a question utilising the equation f ' = c/(c-2v) x f in ultrasound, in med imaging there will probz be a question on PET scan or gamma camera as MRI was in last paper,
Cheers. You better be right. Lol.
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MarieLyon
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#646
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#646
(Original post by Pandit Bandit)
describe and interpret Hubble’s redshift
observations and what he deduced from it?
erm... if the wavelength is small then the galaxy is moving towards us and if the wavelenght is larger then the galaxy is moving away. When do you use that redshift equation?
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InsaneFandom
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#647
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#647
Quick question- in calculations you use the halflife in seconds, right?
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Lengalicious
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#648
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#648
(Original post by InsaneFandom)
Quick question- in calculations you use the halflife in seconds, right?
unless stated otherwise, usually it will ask you to convert the answer you calculate into years and supply the magnitude of seconds within a year that they wish you to use
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yokabasha
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#649
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#649
Do we have to know the exact times and temperatures for the significant changes from the big bang to the present?
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muffingg
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#650
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#650
Do we need to remember the charge, baryon number and strangeness of the quarks?
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Lengalicious
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#651
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#651
(Original post by yokabasha)
Do we have to know the exact times and temperatures for the significant changes from the big bang to the present?
I wouldn't have thought so, my bet is that it would give you a table with the times and ud have to fill in what happens during that time rather than actually having to state the times which would just be useless knowledge
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susan23
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#652
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#652
(Original post by muffingg)
Do we need to remember the charge, baryon number and strangeness of the quarks?
yes
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Oh my Ms. Coffey
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#653
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#653
(Original post by yokabasha)
Do we have to know the exact times and temperatures for the significant changes from the big bang to the present?
Yup, spec says so.
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ChoYunEL
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#654
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#654
Guessing what big question will come up in Physics tomorrow...
Mass spectrometry, Nuclear reactors, Alpha scattering, PET-scan, Transformers, Formation of the universe,
It could be one of these since it is one that hasn't come up yet.
Explain whether the universe is open/closed/flat has been done I believe.
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sizzy33
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#655
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#655
I was thinking maybe some death of star stuff too? There was evolution in one of the paper though so maybe not. What the eff is mass spectrometry?!
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InsaneFandom
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#656
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#656
(Original post by muffingg)
I just hope none of the medical crap comes up!

Order of preference:

Electric Fields
Magnetic Fields
Electromagnetism
Capacitors
Cosmology
Nuclear Physics
.
.
.
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Medical Physics
Aha, mines pretty much the reverse order :p:
The electric/magnetic stuff kills me
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twistedinsanity
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#657
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#657
(Original post by sizzy33)
I was thinking maybe some death of star stuff too? There was evolution in one of the paper though so maybe not. What the eff is mass spectrometry?!
Electric and Magnetic fields in a Mass Spectrometer are used to manipulate the path of an ion. Basically, the ion goes through the Electric field and is accelerated, then when it hits the Magnetic Field, it experiences a force perpendicular to its motion, so it has a circular path. How far it is deflected by the magnetic field depends on the ion's mass - charge ratio. The spectrometer can be set up so it only detects ions of a certain mass - charge ratio. You use it (mostly in Chemistry) to identify substances.
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ChoYunEL
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#658
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#658
Mass Spectrometer
Used to determine the masses of charged ions and their relative abundances.
- A uniform magnetic field is used to deflect the charged ions in a circular path in an evacuated
chamber.
- A moveable detector used to find the radius of the path and the relative abundance of the ions.
- The radius r of the path in the magnetic field region is F = (M * V^2)/r
- The radius that the particle moves in (and hence the place where it hits the sensor) depends on the
different mass to charge ratio.
Example
An electron travelling at 7.5x106 ms-1 enters a region of uniform magnetic field of flux density 60microT.
The electron is initially travelling at right angles to the magnetic field. Find the radius of the circular motion
The magnetic force provides the centripetal acceleration. Bev = mv2/r => 7.5x106 x 1.6x10-19 x 7.5x106 =
9.11x10-31 x (7.5x106)2 / r => r= 0.71m

There is a whole section on it in the OCR A2 text book, Page 104-105
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anshul95
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#659
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#659
(Original post by Lengalicious)
judging by what didnt come up in the last 2011 jan paper, im guessing there will be a question utilising the equation f ' = c/(c-2v) x f in ultrasound, in med imaging there will probz be a question on PET scan or gamma camera as MRI was in last paper,
actually for doppler effect, we only have to describe how to qualitatively obtain a doppler scan i.e. the formula given on that page we don't need to remember. They could however, give it to us and ask us to use it.
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anshul95
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#660
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#660
by the way everyone has forgotten to mention the velocity selector used before the ions enter the magnetic field.
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