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OCR Physics G485 - June 2013 Unit 5 (OFFICIAL THREAD)
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Original post by Namod
3ii? mmmmm 3aii or 3bii?
b(ii) sorry
Original post by Brownie12335
b(ii) sorry
For both of your questions the mark scheme tell us everything:
Original charge on 4.5 µF capacitor is
conserved (28.35 µC)
V = (28.35 µ) / (1.5 + 4.5) µ = 4.7 (V)
conserved (28.35 µC)
V = (28.35 µ) / (1.5 + 4.5) µ = 4.7 (V)
a = F / m a = Eq / m
a = (12000 x 3.2 x 10^-19) / 6.6 x 10^-27)
= 5.82 x 10^11 (m s^-2)
a = (12000 x 3.2 x 10^-19) / 6.6 x 10^-27)
= 5.82 x 10^11 (m s^-2)
What don't you understand?
Original post by Namod
For both of your questions the mark scheme tell us everything:
What don't you understand?
What don't you understand?
I looked at 3bii again, that's fine now. The other one just isn't making sense for some reason...
Original post by Brownie12335
I looked at 3bii again, that's fine now. The other one just isn't making sense for some reason...
The original charge from the circuit in fig 1.1 on the 4.5 µF capacitor is conserved (28.35 µC) you must have worked out the 28.35 µC in 1bi
Therefore Using V = Q/C where C is the total capacitance of the circuit and as the capacitors are in parallel, the capacitance of both capacitors add. C = (1.5 +4.5) µ = 6 µ
V = (28.35 µ) / 6 µ = 4.7 (V) the µ cancel in both sides.
(edited 10 years ago)
Does anyone know the Alpha, beta and gamma penetration. IT CHANGES IN EVERY TIME, EVERY BOOK. I'm tired to change what to remember for this penetration.
What is the "official one" or which one do you know.
At the moment I think its
Alpha - Sheet of paper
Beta - 2-3 mm aluminium
Gamma - 1 cm lead.
What is the "official one" or which one do you know.
At the moment I think its
Alpha - Sheet of paper
Beta - 2-3 mm aluminium
Gamma - 1 cm lead.
(edited 10 years ago)
Original post by Namod
Does anyone know the Alpha, beta and gamma penetration. IT CHANGES IN EVERY TIME, EVERY BOOK. I'm tired to change what to remember for this penetration.
What is the "official one" or which one do you know.
At the moment I think its
Alpha - Sheet of paper
Beta - 2-3 mm aluminium
Gamma - 1 cm lead.
What is the "official one" or which one do you know.
At the moment I think its
Alpha - Sheet of paper
Beta - 2-3 mm aluminium
Gamma - 1 cm lead.
Don't forget the nature of the radiation as well.
For beta I just say a few mm and a few cm for aluminum.
Guys, I have a technical question I need help with.
When you're doing a Q with several sub questions, do you round your answers or not.
eg it says work out charge and you have for the charge 1.3333333 Coulombs so you can put 1.33 for the answer
And then part b, it says work out PD using the charge. Do you use 1.3 recurring or can you just use 1.33 from the answer you rounded to 3 sf?
When you're doing a Q with several sub questions, do you round your answers or not.
eg it says work out charge and you have for the charge 1.3333333 Coulombs so you can put 1.33 for the answer
And then part b, it says work out PD using the charge. Do you use 1.3 recurring or can you just use 1.33 from the answer you rounded to 3 sf?
Original post by eggfriedrice
Don't forget the nature of the radiation as well.
For beta I just say a few mm and a few cm for aluminum.
For beta I just say a few mm and a few cm for aluminum.
yeah the nature is always
Alpha - Helium nucleus
Beta - Electron
Gamma - High frequency electromagnetic wave.
Original post by KD35
Guys, I have a technical question I need help with.
When you're doing a Q with several sub questions, do you round your answers or not.
eg it says work out charge and you have for the charge 1.3333333 Coulombs so you can put 1.33 for the answer
And then part b, it says work out PD using the charge. Do you use 1.3 recurring or can you just use 1.33 from the answer you rounded to 3 sf?
When you're doing a Q with several sub questions, do you round your answers or not.
eg it says work out charge and you have for the charge 1.3333333 Coulombs so you can put 1.33 for the answer
And then part b, it says work out PD using the charge. Do you use 1.3 recurring or can you just use 1.33 from the answer you rounded to 3 sf?
You use the answer you put as b
In this case the 1.33 rounded to 3s.f
Original post by KD35
Guys, I have a technical question I need help with.
When you're doing a Q with several sub questions, do you round your answers or not.
eg it says work out charge and you have for the charge 1.3333333 Coulombs so you can put 1.33 for the answer
And then part b, it says work out PD using the charge. Do you use 1.3 recurring or can you just use 1.33 from the answer you rounded to 3 sf?
When you're doing a Q with several sub questions, do you round your answers or not.
eg it says work out charge and you have for the charge 1.3333333 Coulombs so you can put 1.33 for the answer
And then part b, it says work out PD using the charge. Do you use 1.3 recurring or can you just use 1.33 from the answer you rounded to 3 sf?
I personally don't round until I get the final answer, rounding too soon has the potential to cause errors.
Original post by Picture~Perfect
I personally don't round until I get the final answer, rounding too soon has the potential to cause errors.
you have to round off to give an answer for part a.
Original post by Namod
You use the answer you put as b In this case the 1.33 rounded to 3s.f
In this case the 1.33 rounded to 3s.fOk, what about when it says show that bla bla is ABOUT 500.
Do you use 500 or the answer you get. eg 497. On mark schemes, they say different things about this issue.
Original post by Namod
Another thing that let me down in F324 is the time factor, I ran out of time.
So is there any tip so I don't run out of time in this exam?
So is there any tip so I don't run out of time in this exam?
If you can't do a question, seriously just move on.
Also read each question carefully so you know what you're doing before you start because it'll waste time if you realise you're not actually answering the questions.
For the long answer questions, it's literally just remembering your model answers so you could practice writing them quickly, giving you time to do the mathematical ones.
Original post by eggfriedrice
If you can't do a question, seriously just move on.
Also read each question carefully so you know what you're doing before you start because it'll waste time if you realise you're not actually answering the questions.
For the long answer questions, it's literally just remembering your model answers so you could practice writing them quickly, giving you time to do the mathematical ones.
Also read each question carefully so you know what you're doing before you start because it'll waste time if you realise you're not actually answering the questions.
For the long answer questions, it's literally just remembering your model answers so you could practice writing them quickly, giving you time to do the mathematical ones.
Need to get the Past Papers for Phys 4 done soon! Thanks for the advice. And your name "EggFriedRice" is priceless.
Death of a Star
Hydrogen is used up (1)
Loss of radiation pressure (1)
Core contracts rapidly (1)
Large temperature rise (1)
Helium fusion (1)
Expansion of outer layers - which cool (1)
Red giant is formed (1)
History of the Universe
Big Bang occurred (1)
Photons produce particles of matter and antimatter (1)
An excess of matter over antimatter occurs (1)
Nuclear fusion occurs (1)
Nuclear fusion stops (1)
Atoms form (1)
Stars and galaxies form (1)
Nuclear fusion occurs in stars (1)
Life starts (1)
Cosmic Microwave Background Radiation
In the microwave region (about wavelength = 1mm) (1)
Is isotropic, showing that the origin is beyond our galaxy (1)
Corresponds to a classical Planckian curve for a temperature of 2.7K (1)Is composed of photons (1) which became visible as soon as the universe consisted of neutral atoms and so became transparent (1)
The original short wavelength (1) photons have expanded in wavelength as the universe has expanded (1)
X-Ray Tube
High voltage accelerates electrons (1)
Electrons collide with anode (1)
1% of the energy is released in all directions as X-rays (1)
Rest of kinetic energy is released as heat (1)
Compton Scattering
An X-ray photon (1) of energy 0.5 MeV < E < 5.0 MeV loses only a fraction of its energy to an atomic electron in the absorbing material (1)
The interaction between the photon and the electron is inelastic (1)The scattered X-ray photon has less energy than before (1) so its wavelength is greater (1)
The Compton electron travels in a different direction from the scattered photon (1)because momentum must be conserved (1)
Pair Production
A high energy X-ray photon (1) of energy E > 1.02 MeV, passing through the electric field of the nucleus suddenly produces an electron-positron pair (1)Its energy appears as the mass of the electron and the positron (1)The positron is soon annihilated when it collides with another electron (1)(This process is not very important in diagnostic X-rays because the X-ray energies used are too low)
Medical Tracing
Use a radionuclide (1)
Prepare source (radioisotopes are short-lived) (1)Inject into patient (1)Wait to disperse around the body (1)
Expose to radiation (1)
Caution until radiation has left body (1)
Technetium-99 is most commonly used (1)
Alpha-Scattering Experiment (Gold Leaf Experiment)
Most of the alpha particles went straight through (1) therefore the atom is mostly empty space (1)
A very small number of alpha particles were repelled (1) through angles more than 90 degrees (1)
This showed the existence of a tiny (1) positive (1)nucleus
(The size of the nucleus is about 10^-14 m)
Positron Emission Tomography (PET)
A positron emitting tracer is used (1)The positron annihilates with an electron inside the patient (1)
This produces two gamma ray (1) photons which travel in opposite directions (1)The patient is surrounded by a ring of gamma detectors (1)
The arrival times of the photons (delay time) indicates the location of where the positron was emitted (1)(1)
A 3D image is created by the computer (1)
Ultrasound Scanning
A piezoelectric crystal (or transducer) (1) is used to send pulses of ultrasound into the patient (1)
Ultrasound wave is reflected (1) at the boundary of tissue (1)
The intensity of the reflected signal depends on the acoustic impedances at the boundary (1) this identifies the type of tissue (1)
The time of delay is used to determine the thickness (1)
A-scan: Uses one direction only (1) e.g. depth finding
B-scan: Uses a number of sensors to build up an image (1)
Carbon Dating
Living things take in carbon dioxide and stop taking in carbon dioxide after they die (1)The ratio of carbon-14 to carbon-12 nuclei for the relic sample is determined (1)
The age of the relic sample is found using equations (1)
Limitations:
The ratio of carbon-14 to carbon-12 is assumed to be constant (1)
The count rate from the relic may be comparable to the background count rate (1)
Formation and Life of Stars
Regions of higher density in space attract each other (1) forming nebulae (1)
Stars are formed from these nebulae (1)
Gravitational collapse (1) occurs when the nebula continues to grow in density and the attractive force becomes stronger (1)
The temperature of the cloud increases (1) due to its kinetic energy increasing (gravitational potential energy is converted into kinetic) (1)
When the pressure and temperature is substantial fusion occurs (1) and hydrogen fuses to form helium (1)
A stable (main sequence) star is formed (1) when it is in thermal equilibrium (1) (the thermal pressure is equal to the gravitational pressure
Evidence of the Big Bang
Galaxies are moving apart (1)Therefore they must have started from a point (1)
Galaxies that are further away travel faster (1)
There is a 2.7K (Planckian curve) microwave background radiation (1)
There is more helium in the universe than expected (1)
Magnetic Resonance Imaging (MRI)
Some nuclei behave as small magnets (1) they line up in the magnetic field (1)
A strong magnetic force is required (1)
Nuclei precess at a frequency known as the Larmor frequency (1)
A coil sends out a pulse of radio waves which cause resonance (1) the nuclei absorb a lot of energy (1)
When the radio frequency pulse is stopped, the nuclei relax (1) and they emit the energy they previously gained as a radio frequency signal (1)
The emitted radio frequency signal is detected by the coil (1)
Different tissues/materials can be detected by the different relaxation times (1)of the hydrogen nuclei in the tissue (1)
A non-uniform (1) magnetic field is used (1) so that the Larmor frequency is not the same everywhere (1) which allows the location of the nuclei in the body to be found (1)
Because the 7-markers are nasty.
Hydrogen is used up (1)
Loss of radiation pressure (1)
Core contracts rapidly (1)
Large temperature rise (1)
Helium fusion (1)
Expansion of outer layers - which cool (1)
Red giant is formed (1)
History of the Universe
Big Bang occurred (1)
Photons produce particles of matter and antimatter (1)
An excess of matter over antimatter occurs (1)
Nuclear fusion occurs (1)
Nuclear fusion stops (1)
Atoms form (1)
Stars and galaxies form (1)
Nuclear fusion occurs in stars (1)
Life starts (1)
Cosmic Microwave Background Radiation
In the microwave region (about wavelength = 1mm) (1)
Is isotropic, showing that the origin is beyond our galaxy (1)
Corresponds to a classical Planckian curve for a temperature of 2.7K (1)Is composed of photons (1) which became visible as soon as the universe consisted of neutral atoms and so became transparent (1)
The original short wavelength (1) photons have expanded in wavelength as the universe has expanded (1)
X-Ray Tube
High voltage accelerates electrons (1)
Electrons collide with anode (1)
1% of the energy is released in all directions as X-rays (1)
Rest of kinetic energy is released as heat (1)
Compton Scattering
An X-ray photon (1) of energy 0.5 MeV < E < 5.0 MeV loses only a fraction of its energy to an atomic electron in the absorbing material (1)
The interaction between the photon and the electron is inelastic (1)The scattered X-ray photon has less energy than before (1) so its wavelength is greater (1)
The Compton electron travels in a different direction from the scattered photon (1)because momentum must be conserved (1)
Pair Production
A high energy X-ray photon (1) of energy E > 1.02 MeV, passing through the electric field of the nucleus suddenly produces an electron-positron pair (1)Its energy appears as the mass of the electron and the positron (1)The positron is soon annihilated when it collides with another electron (1)(This process is not very important in diagnostic X-rays because the X-ray energies used are too low)
Medical Tracing
Use a radionuclide (1)
Prepare source (radioisotopes are short-lived) (1)Inject into patient (1)Wait to disperse around the body (1)
Expose to radiation (1)
Caution until radiation has left body (1)
Technetium-99 is most commonly used (1)
Alpha-Scattering Experiment (Gold Leaf Experiment)
Most of the alpha particles went straight through (1) therefore the atom is mostly empty space (1)
A very small number of alpha particles were repelled (1) through angles more than 90 degrees (1)
This showed the existence of a tiny (1) positive (1)nucleus
(The size of the nucleus is about 10^-14 m)
Positron Emission Tomography (PET)
A positron emitting tracer is used (1)The positron annihilates with an electron inside the patient (1)
This produces two gamma ray (1) photons which travel in opposite directions (1)The patient is surrounded by a ring of gamma detectors (1)
The arrival times of the photons (delay time) indicates the location of where the positron was emitted (1)(1)
A 3D image is created by the computer (1)
Ultrasound Scanning
A piezoelectric crystal (or transducer) (1) is used to send pulses of ultrasound into the patient (1)
Ultrasound wave is reflected (1) at the boundary of tissue (1)
The intensity of the reflected signal depends on the acoustic impedances at the boundary (1) this identifies the type of tissue (1)
The time of delay is used to determine the thickness (1)
A-scan: Uses one direction only (1) e.g. depth finding
B-scan: Uses a number of sensors to build up an image (1)
Carbon Dating
Living things take in carbon dioxide and stop taking in carbon dioxide after they die (1)The ratio of carbon-14 to carbon-12 nuclei for the relic sample is determined (1)
The age of the relic sample is found using equations (1)
Limitations:
The ratio of carbon-14 to carbon-12 is assumed to be constant (1)
The count rate from the relic may be comparable to the background count rate (1)
Formation and Life of Stars
Regions of higher density in space attract each other (1) forming nebulae (1)
Stars are formed from these nebulae (1)
Gravitational collapse (1) occurs when the nebula continues to grow in density and the attractive force becomes stronger (1)
The temperature of the cloud increases (1) due to its kinetic energy increasing (gravitational potential energy is converted into kinetic) (1)
When the pressure and temperature is substantial fusion occurs (1) and hydrogen fuses to form helium (1)
A stable (main sequence) star is formed (1) when it is in thermal equilibrium (1) (the thermal pressure is equal to the gravitational pressure
Evidence of the Big Bang
Galaxies are moving apart (1)Therefore they must have started from a point (1)
Galaxies that are further away travel faster (1)
There is a 2.7K (Planckian curve) microwave background radiation (1)
There is more helium in the universe than expected (1)
Magnetic Resonance Imaging (MRI)
Some nuclei behave as small magnets (1) they line up in the magnetic field (1)
A strong magnetic force is required (1)
Nuclei precess at a frequency known as the Larmor frequency (1)
A coil sends out a pulse of radio waves which cause resonance (1) the nuclei absorb a lot of energy (1)
When the radio frequency pulse is stopped, the nuclei relax (1) and they emit the energy they previously gained as a radio frequency signal (1)
The emitted radio frequency signal is detected by the coil (1)
Different tissues/materials can be detected by the different relaxation times (1)of the hydrogen nuclei in the tissue (1)
A non-uniform (1) magnetic field is used (1) so that the Larmor frequency is not the same everywhere (1) which allows the location of the nuclei in the body to be found (1)
Because the 7-markers are nasty.
Original post by Kreayshawn
from G482 we know KE = qV
so we just equate it here
qV = 1/2mv^2
therefore,
(2qv)/m = v^2
square root[(2qV)/m] = v
hope that makes sense
does anyone have mark scheme bullet points on the gamma camera procedure? (like a model answer or something I can memorise)
so we just equate it here
qV = 1/2mv^2
therefore,
(2qv)/m = v^2
square root[(2qV)/m] = v
hope that makes sense
does anyone have mark scheme bullet points on the gamma camera procedure? (like a model answer or something I can memorise)
I'm a bit late but for the Gamma Camera question if you check the attachments on the first page of the document and download the one called "Essay Type Questions - G485.pdf" there's a good 5 bullet points in there
Original post by Kreayshawn
from G482 we know KE = qV
so we just equate it here
qV = 1/2mv^2
therefore,
(2qv)/m = v^2
square root[(2qV)/m] = v
hope that makes sense
does anyone have mark scheme bullet points on the gamma camera procedure? (like a model answer or something I can memorise)
so we just equate it here
qV = 1/2mv^2
therefore,
(2qv)/m = v^2
square root[(2qV)/m] = v
hope that makes sense
does anyone have mark scheme bullet points on the gamma camera procedure? (like a model answer or something I can memorise)
Model answers for all the big questions I could find are on page 41
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