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

ziigmund
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ty choy much appreciated
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sulexk
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(Original post by ChoYunEL)
G485

Electric field strength: The electric field strength at a point is the force per unit charge exerted on a positive charge placed at that point.
Magnetic flux density: Defined by the equation: ? = (F/I*L), where ? is the magnetic flux density, F is the forces experienced by a conductor carrying a current I and L is the length of the conductor.
Tesla: 1 Tesla is the magnetic flux density when a wire carrying a current of 1 Amp, is placed at right angles to the magnetic field, experiences a force of 1 N per metre of its length.
Magnetic flux: The magnetic flux, ?, through an area, A, is defined as: ?=?*A where
? is the component of the magnetic flux density perpendicular to the area A.
Weber: 1 Weber is equal to 1 Tesla metre squared, 1Wb = 1Tm2
Magnetic flux linkage: The product of the magnetic flux and the number of turns in a coil: Magnetic flux linkage = ?*A*N or ?*A*N*(cos ?) where ? is the magnetic flux density, A is the cross sectional area of a coil and N is the number of coils.
Capacitance: The capacitance of a capacitor is the charge stored per unit of potential difference across it.
Farad: 1 Farad is 1 Coulomb per Volt. 1F = 1CV-1
Proton Number: The proton number (or atomic number) is the number of protons in a nucleus. Symbol = Z
Nucleon number: The nucleon number (or mass number) is the number of protons and neutrons in a nucleus. Symbol = A
Isotopes: Isotopes are nuclei of the same element with a different number of neutrons but the same number of protons. They have the same proton number but a different nucleon number.
Binding energy: The minimum energy needed to pull a nucleus apart into its separate nucleons.
Binding energy per nucleon: The minimum energy needed to pull an individual nucleon from a nucleus. Calculated by dividing the Binding Energy by the nucleon number.
Activity: The activity, A, of a radioactive sample is the rate at which nuclei decay or disintegrate. Unit = Becquerel (Bq). 1 Bq = 1 s-1
Decay constant: The probability that an individual nucleus will decay per unit time interval. Symbol = ? and units are s-1, min-1, day-1 or any unit of time raised to power minus 1.
Half-life: The half life, t ½, of a radioisotope is the mean time taken for half the active (or undecayed) nuclei in a sample to decay.
Intensity: Intensity is the Power per unit cross-sectional Area.
Critical density: The density of the universe that will give rise to a flat universe, given by the equation: ?0 = (3*H02 / 8?G), where H0 is the Hubble constant and G is the Gravitational constant.
Astronomical Unit (AU): The average distance of the Earth from the sun.
Light-year (ly): The distance travelled by light through a vacuum in one year.
Parsec(Pc): The distance that gives a parallax angle of 1 arc second. Often a diagram is needed here, please refer to your book for this.

These definitions are used by the exam board and you must be able to quote them word for word.

Descriptions of the following experiments, among others, may be useful:

• Investigating Coulombs Law.
• Comparing Gravitational and Electric Fields.
• Flemings Left Hand Rule
• How a mass spectrometer works.
• How transformer work.
• How capacitors charge and discharge.
• The alpha scattering experiment.
• How nuclear power works.
• How to differentiate between different forms of radioactivity.
• How to measure the Half-life of a radioisotope.
• How Carbon Dating works.
• How X-Rays are generated.
• How to improve the contrast of X-Rays.
• How CAT Scanning works
• Contrast and Compare various diagnostic methods e.g. ultrasound and X-Rays.
• How the gamma camera works.
• How PET scanning works.
• How MRI scanning works and the advantages and disadvantages of this.
• How to produce Ultrasound waves – the piezoelectric effect.
• The difference between A and B Scans.
• The basis of the Cosmological principle.
• The life and deaths of stars.
• Describe Oblers’ Paradox.
• Describe red shift.
• How to convert between parsecs and SI units.
• The evidence for the Hot Big Bang model of the universe.
• The three fates of the universe.
• Ensure that you can use X=X0 e?t.

Please note that you have to be very precise when you answer long answer questions. Look through past exam papers and mark schemes to gain a sense of what you need to write.
Thank you for this- wonderful!

I shall try my best to write something for each bullet point.
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sulexk
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(Original post by ChoYunEL)
G485

Electric field strength: The electric field strength at a point is the force per unit charge exerted on a positive charge placed at that point.
Magnetic flux density: Defined by the equation: ? = (F/I*L), where ? is the magnetic flux density, F is the forces experienced by a conductor carrying a current I and L is the length of the conductor.
Tesla: 1 Tesla is the magnetic flux density when a wire carrying a current of 1 Amp, is placed at right angles to the magnetic field, experiences a force of 1 N per metre of its length.
Magnetic flux: The magnetic flux, ?, through an area, A, is defined as: ?=?*A where
? is the component of the magnetic flux density perpendicular to the area A.
Weber: 1 Weber is equal to 1 Tesla metre squared, 1Wb = 1Tm2
Magnetic flux linkage: The product of the magnetic flux and the number of turns in a coil: Magnetic flux linkage = ?*A*N or ?*A*N*(cos ?) where ? is the magnetic flux density, A is the cross sectional area of a coil and N is the number of coils.
Capacitance: The capacitance of a capacitor is the charge stored per unit of potential difference across it.
Farad: 1 Farad is 1 Coulomb per Volt. 1F = 1CV-1
Proton Number: The proton number (or atomic number) is the number of protons in a nucleus. Symbol = Z
Nucleon number: The nucleon number (or mass number) is the number of protons and neutrons in a nucleus. Symbol = A
Isotopes: Isotopes are nuclei of the same element with a different number of neutrons but the same number of protons. They have the same proton number but a different nucleon number.
Binding energy: The minimum energy needed to pull a nucleus apart into its separate nucleons.
Binding energy per nucleon: The minimum energy needed to pull an individual nucleon from a nucleus. Calculated by dividing the Binding Energy by the nucleon number.
Activity: The activity, A, of a radioactive sample is the rate at which nuclei decay or disintegrate. Unit = Becquerel (Bq). 1 Bq = 1 s-1
Decay constant: The probability that an individual nucleus will decay per unit time interval. Symbol = ? and units are s-1, min-1, day-1 or any unit of time raised to power minus 1.
Half-life: The half life, t ½, of a radioisotope is the mean time taken for half the active (or undecayed) nuclei in a sample to decay.
Intensity: Intensity is the Power per unit cross-sectional Area.
Critical density: The density of the universe that will give rise to a flat universe, given by the equation: ?0 = (3*H02 / 8?G), where H0 is the Hubble constant and G is the Gravitational constant.
Astronomical Unit (AU): The average distance of the Earth from the sun.
Light-year (ly): The distance travelled by light through a vacuum in one year.
Parsec(Pc): The distance that gives a parallax angle of 1 arc second. Often a diagram is needed here, please refer to your book for this.

These definitions are used by the exam board and you must be able to quote them word for word.

Descriptions of the following experiments, among others, may be useful:

• Investigating Coulombs Law.
• Comparing Gravitational and Electric Fields.
• Flemings Left Hand Rule
• How a mass spectrometer works.
• How transformer work.
• How capacitors charge and discharge.
• The alpha scattering experiment.
• How nuclear power works.
• How to differentiate between different forms of radioactivity.
• How to measure the Half-life of a radioisotope.
• How Carbon Dating works.
• How X-Rays are generated.
• How to improve the contrast of X-Rays.
• How CAT Scanning works
• Contrast and Compare various diagnostic methods e.g. ultrasound and X-Rays.
• How the gamma camera works.
• How PET scanning works.
• How MRI scanning works and the advantages and disadvantages of this.
• How to produce Ultrasound waves – the piezoelectric effect.
• The difference between A and B Scans.
• The basis of the Cosmological principle.
• The life and deaths of stars.
• Describe Oblers’ Paradox.
• Describe red shift.
• How to convert between parsecs and SI units.
• The evidence for the Hot Big Bang model of the universe.
• The three fates of the universe.
• Ensure that you can use X=X0 e?t.

Please note that you have to be very precise when you answer long answer questions. Look through past exam papers and mark schemes to gain a sense of what you need to write.

I have a better idea, anyone up for this?

Tonights quiz these questions! (the bullet points)

What do you say?
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Ralphus J
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Choy i dont think you actually need to be able to describe certain experiments, like in the last units. Unless it literally says "describe such and such experiment" in the syllabus statement [in which the only ones are alpha scattering, mass spectrometer (which i think will come up!) and gamma camera which isnt really an experiment].
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mauvetard
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Im up for the quiz, I think its a good idea revision wise. Does anyone have an idea of where to get more past papers? , I've exhausted all the ones I have
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ChoYunEL
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(Original post by Ralphus J)
Choy i dont think you actually need to be able to describe certain experiments, like in the last units. Unless it literally says "describe such and such experiment" in the syllabus statement [in which the only ones are alpha scattering, mass spectrometer (which i think will come up!) and gamma camera which isnt really an experiment].
It says it maybe useful. This is a copy and paste.
If you are able to describe all the points - you've sussed G485.

• How Carbon Dating works.
"Haha, what a joke, Carbon Dating?"
*In the January G485 exam*
"Ah sh*t... Carbon dating."
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ChoYunEL
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(Original post by mauvetard)
Im up for the quiz, I think its a good idea revision wise. Does anyone have an idea of where to get more past papers? , I've exhausted all the ones I have
You can go to other exam boards and try their question...
That's what I went down to in Jan... it didn't help
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M_I
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Does a neutron star form before a supernova and then the neutron star is left behind?
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mauvetard
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(Original post by ChoYunEL)
You can go to other exam boards and try their question...
That's what I went down to in Jan... it didn't help
Actually sounds like fun, Ive gotten so bored of OCR I think its time to test the waters ..
I'd see how things go, hope it helps this time
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Ralphus J
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Since your doing this bullet point thing can someone do the "describe how the PET scan works"
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sulexk
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(Original post by Ralphus J)
Since your doing this bullet point thing can someone do the "describe how the PET scan works"
I shall do that along with doing my best to describe everything on that list

I will need about 2-3 hours.
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CapsLocke
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(Original post by Ralphus J)
Since your doing this bullet point thing can someone do the "describe how the PET scan works"
Pet Scan

Patient swallows/injects a B+ emitter which is attached too some sort of substance which the body will use. That substance will travel to the certain part of the body which wants to be monitored, and the substance will be used up, leaving just the B+ emitter. The B+ emitter will emit a positron which will annihilate will an electron almost immediately. When the annihilation occurs the 2 gamma photons will be released in opposite directions, which will then be detected by gamma cameras which surrounds the patient
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sulexk
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(Original post by M_I)
Does a neutron star form before a supernova and then the neutron star is left behind?
Hello,

Well what happens is that the outer shells surrounding the core rapidly collapse rebound against the solid neutron core and explode off into space, this is the supernova(the big explosion), leaving behind the neutron core. So, a neutron star, strictly speaking, forms after a supernova.
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sulexk
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(Original post by CapsLocke)
Pet Scan

Patient swallows/injects a B+ emitter which is attached too some sort of substance which the body will use. That substance will travel to the certain part of the body which wants to be monitored, and the substance will be used up, leaving just the B+ emitter. The B+ emitter will emit a positron which will annihilate will an electron almost immediately. When the annihilation occurs the 2 gamma photons will be release in opposite directions, which will then be detected by gamma cameras which surrounds the patient
Great explanation!
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ChoYunEL
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If anything you want to look through the a-level spec... it's too large to show everything but
Attached files
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jam.wa
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Can anyone tell me the difference between A-scan and B-scan?
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ChoYunEL
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(Original post by jam.wa)
Can anyone tell me the difference between A-scan and B-scan?
A-scan in one direction only / range or distance or depth finding
B-scan uses a number of sensors or a sensor in different positions / angles (to build up a 2D/3D image)

A B-scan is not many A-scans
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M_I
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(Original post by sulexk)
Hello,

Well what happens is that the outer shells surrounding the core rapidly collapse rebound against the solid neutron core and explode off into space, this is the supernova(the big explosion), leaving behind the neutron core. So, a neutron star, strictly speaking, forms after a supernova.
Ah ok...thanks.
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rebmu
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(Original post by jam.wa)
Can anyone tell me the difference between A-scan and B-scan?
basically an a scan displays information as a peak on a cro screen, the higher the peak the greater the reflection, the a stands for amplitude whereas a b scan converts this into a pixel the brightness depending on how much ultrasound is reflected, b stands for brightness. these pixels then form a 2d image as many beams are sent out and they reflect at various points.
have a look at my presentation explains it beautifully
Attached files
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Lengalicious
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Ok guys answer me this, magnetic fields are caused by moving charge, neutrons stars are neutral, therefore no moving charge, yet they have some of the largest magnetic fields in the universe? I know they emit EM radiation by NMR but still don't get why they have such large magnetic fields?
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