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# OCR Physics A G485: 28th June 2016 watch

1. Do we need the know the relationship between Mew (attenuation coefficient) and Z and also the relationship between Mew and E as part of the attenuation mechanisms (photoelectric effect/compton/pair production)?
2. (Original post by Hassan55)
Do we need the know the relationship between Mew (attenuation coefficient) and Z and also the relationship between Mew and E as part of the attenuation mechanisms (photoelectric effect/compton/pair production)?
If by Z you mean the acoustic impedance then no, because they are unrelated. Z is for ultrasound, "Mew" is for X-rays.

"Mew" and E aren't related either. The energy the photons have is not influenced by the material they enter.
You need to know that with a higher "Mew", the photons are interacting with the material more, so the intensity after the same distance is lower.
You also need to know that depending on the energy the photon has it interacts differently with matter. Low energy --> photoelectric effect, mid energy --> compton scattering, high energy --> pair production.
3. Hi, does anyone know how to get an A* in A level Physics?
4. min 90% average UMS across A2 modules. (+Overall min 80% (including AS))
5. I'm just going to post some stuff here that I'm currently revising. It's good recap for me and some of you might find it useful lol.

Velocity Selector:
-2 parallel opposite charged plates create an electric field.
-A Mag. field is applied at right angle to the electric field.
-Charged particles with different speeds enter on side of the velocity selector.
-Only those with a particular speed will make it straight through to the other side.
-For the charged particles that travel straight through, the electric force experienced by the particle is equal to the magnetic force experienced by the charge.
-Therefore EQ = BQv
v = E / B, only charged particles with that speed will make it straight though to the other side.
6. Does anyone know if weak force has any effects on hadrons or does it just effect leptons because in the june 2011 paper they ask for the three forces effecting protons and neutrons (question 6B june 2011) but i thought that they would be effected by four forces (weak, strong, gravitational and electrostatic) thanks for any help
Attached Images
7. 62267-question-paper-unit-g485-fields-particles-and-frontiers-of-physics.pdf (151.3 KB, 101 views)
8. 58522-mark-scheme-unit-g485-fields-particles-and-frontiers-of-physics-june.pdf (281.4 KB, 105 views)
9. (Original post by ukcolBehT)
If by Z you mean the acoustic impedance then no, because they are unrelated. Z is for ultrasound, "Mew" is for X-rays.

"Mew" and E aren't related either. The energy the photons have is not influenced by the material they enter.
You need to know that with a higher "Mew", the photons are interacting with the material more, so the intensity after the same distance is lower.
You also need to know that depending on the energy the photon has it interacts differently with matter. Low energy --> photoelectric effect, mid energy --> compton scattering, high energy --> pair production.
By Z I mean proton number and if you look on page 231 of OCR Advanced Physics, Physics 2 for OCR, it says there is a relationship between attenuation coefficient and proton number. It also describes the relationship of attenuation coefficient mew and energy E of incident x ray photon for each of photoelectric effect, Compton and pair production
10. Electromagnetism:

Moving charged particles create a magnetic field, so when they stop, the magnetic field disappears. So a Magnetic field can be created by moving a current carrying conductor in a magnetic field.
Key points:
- Field lines are concentric around the conductor, it gets weaker and weaker.
-You can use the right-hand rule to find direction of current or field. Thumb will be current and the wrap of your hand will be the direction of the magnetic field.

Solenoid:
-Uniform field inside it.
-Acts like a magnetic bar, it has North and South poles.

Flemings left-hand rule:
When 2 magnetic fields are close together, their magnetic fields interact so they experience a force.

So the current carrying conductor placed on in a magnetic field will experience a force because of the magnetic fields interacting.

The direction of that force and be found using that rule, where your thumb is the Force, middle finder is current, index is mag field.

Magnetic flux density, B = F / IL [Tesla, T] 1T = 1 F A^-1 m^-1 (strength of magnetic field), also leads to F = BIL
Tesla - When a wire carrying a current of 1 amp is placed at right angle to the magnetic field, it experiences a force of 1 Newton per meter of its length.

Each tiny charge inside the current carrying conductor experiences a tiny force, hence the BIL force, it is the new force of all of those tiny forces.

that tiny force of the moving charges can be found by using F = BQv (for electron Bev)
When the charge is inside the perpendicular field, it will have a circular path, and the BQv, will be the centripetal force.
So we need to use the circular motion equations with these types of questions.

Magnetic flux = BA, flux density * cross sectional area normal to the field. Unit = Weber [Wb]
For other angels = BAcostheta

Everytime the flux linkage is changed, there is an induced emf in the circuit.

His law:
The magnitude of the induced emf is equal to the rate of change of magnetic flux linkage,
therefore E = change in linkage / change in time.

I don't have time anymore lol, need to continue to study but that is not all of electromagnetism.
11. (Original post by Hassan55)
By Z I mean proton number and if you look on page 231 of OCR Advanced Physics, Physics 2 for OCR, it says there is a relationship between attenuation coefficient and proton number. It also describes the relationship of attenuation coefficient mew and energy E of incident x ray photon for each of photoelectric effect, Compton and pair production

Hmmhm ok, I have a different book, and nowhere does it mention those relationships. Interesting.

But to answer your question, I am sure you do not need to know it, because it is not on the specification, and my book, officially endorsed by OCR, doesn't cover it.

In the spec it says "describe how X-rays interact with matter (limited to photoelectric effect, Compton Effect and pair production);"

I'm certain this doesn't include those relationships, and focuses on the qualitative description of the interactions.
13. guys how your revision going??
btw, would i loose or get marks if i leave the answer in 3s.f but m.s says 2sf??
14. Does anyone have the June 2015 paper and mark scheme??
15. (Original post by Howshotmyexamis)
btw, would i loose or get marks if i leave the answer in 3s.f but m.s says 2sf??
Yes however throughout the whole paper you will only loose 1 mark for Sig Fig error so any substituent errors will not loose you marks.
16. The 2015 conveyor belt calculation question I DONT GET IT AT ALL could someone go through how we are supposed to do that question?
17. What medical imaging questions were there in the 2015 paper?
18. Hyped for tomorrow?
19. (Original post by Howshotmyexamis)
btw, would i loose or get marks if i leave the answer in 3s.f but m.s says 2sf??
No I think there's a bit at the start of the mark scheme which basically says that any more than what is said is fine UNLESS it says to an appropriate number of s.f.
20. Hoping for a lot of astro questions tomorrow! anyone have any favourites they would love??
21. I think there will definitely be an MRI question tomorrow as there wasn't one in last year's paper

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