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June 2011 G485-Fields, Particles and Frontiers of Physics

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Reply 660
Avatar for scotzbhoy
scotzbhoy
Original post by muffingg
Do we need to remember the charge, baryon number and strangeness of the quarks?

Yes, it's not difficult to remember though. Charge= 2/3 for U and -1/3 for the others, Baryon= 1/3 for each and Strangeness= -1 for S and 0 for the others.
Reply 661
Avatar for susan23
susan23
3
can someone explain strong force to me?
Reply 662
Avatar for scotzbhoy
scotzbhoy
Can anyone explain the Piezoelectric effect and how it's used in ultrasound? Thanks.
Original post by scotzbhoy
Yes, it's not difficult to remember though. Charge= 2/3 for U and -1/3 for the others, Baryon= 1/3 for each and Strangeness= -1 for S and 0 for the others.


Done. Memorized them. :smile: Hope they ask a 6 mark question just asking for their values haha.
Reply 664
Avatar for jam.wa
jam.wa
8
Original post by susan23

Original post by susan23
can someone explain strong force to me?


- Only acts on hadrons
- Range = 10^-15
- Independant of charge
- Attractive between nucleons from 2.4 to 5 x 10^-15 m
- Repulsive between nucleons <2.4 x 10^-15 m
Original post by susan23
can someone explain strong force to me?


There is an electrostatic force of repulsion and a force of gravity, but gravity is too weak to balance the E. Therefore there is another force, the SNF. It is attractive below 5fm but below 2.4fm it becomes repulsive (so as not to squash the particles). Between those, it follows an inverse square law for its intensity, but after 5fm (about the size of a nucleus) it falls rapidly. Therefore, it's very short ranged


Also, when would you need to use the Avogadro constant and what's the formula?

Is it Total no. of particles = mass per nucleon x avogadro?
(edited 12 years ago)
Reply 666
Avatar for susan23
susan23
3
Original post by jam.wa
- Only acts on hadrons
- Range = 10^-15
- Independant of charge
- Attractive between nucleons from 2.4 to 5 x 10^-15 m
- Repulsive between nucleons <2.4 x 10^-15 m


do we need to know the measurements I dont get them?
and does the strong force at on neutrons? does electrostatic force at on them? lol i feel stupid....I know they dont have a charge so i think not.
Reply 667
Avatar for lpmad
lpmad
has anyone got the specimen mark scheme?
Do we need to know the temperature and dates of the evolution of the earth or just be able to describe what happens?
Original post by lpmad
has anyone got the specimen mark scheme?


You can get if from here:

http://www.ocr.org.uk/download/assess_mat/ocr_7977_sam_gce_unit_g485.pdf
Reply 670
Avatar for jam.wa
jam.wa
8
Original post by scotzbhoy

Original post by scotzbhoy
Can anyone explain the Piezoelectric effect and how it's used in ultrasound? Thanks.


Piezoelectric effect: Changing the volume of a certian type of crystal induces a voltage but also applying a voltage across the crystal makes it contract/relax at the applied frequency.

Use in ultrasound - The transducer
Transmission:
-Varying voltage applied to crystal
-Crystal contracts/relaxes at applied frequency
-When frequency = Larmour frequency, resonance occurs
-Ultrasound waves transmitted

Reception
-Ultrasound waves strike crystal
-Varying stress results in a voltage
-Voltage registered, time of echo recorded
Reply 671
Avatar for jamedz
jamedz
here's a bit of bed time reading for you :wink: it's a few summaries of just about every long answer question they could ask.. don't know how I've manged to do all this today :P its like half an EPQ.. ah well it should hopefully be worth it :tongue: enjoy :biggrin:
Possible G485 essay and long answer questions 2011 (JR).pdf542.3KB
Reply 672
Avatar for ChoYunEL
ChoYunEL
1
Original post by anshul95
by the way everyone has forgotten to mention the velocity selector used before the ions enter the magnetic field.


You mean Energy = Voltage * Charge
And Energy = 1/2 * Mass * Velocity^2
Therefore, VQ=(M * V^2)/2
and (2VQ/M) = V^2

(2 lots of Voltage * Charge ) / Mass = Velocity squared.
Original post by scotzbhoy
Can anyone explain the Piezoelectric effect and how it's used in ultrasound? Thanks.


Piezoelectric crystals (sodium tritinate?) deform when a P.d is put across them and when they deform they produce a P.d (due to the change in crystal structures?). When an alternating voltage is passed through them they vibrate at the same frequency as the alternating voltage.

This can be used to transmit Ultrasound waves by applying an alternating voltage to the crystal to produce ultrasound waves and also receive ultrasound waves changing these vibrations into alternating voltages.

A Piezoelectric is heavily damped.
Original post by M_I
How does the cosmic background raditaion being linked with 3K prove the big bang model?


the radiation is at a temperature of 3K, and is a remnant of the heat radiation which was spread out in the Universe shortly after the big bang. it's cooled to this temperature because the Universe has been expanding, showing that the Universe isnt static, therefore supporting the Big Bang Model :smile:
Reply 675
Avatar for susan23
susan23
3
Original post by jamedz
here's a bit of bed time reading for you :wink: it's a few summaries of just about every long answer question they could ask.. Don't know how i've manged to do all this today :tongue: its like half an epq.. Ah well it should hopefully be worth it :tongue: enjoy :d


omg i love youu!!!!!!!!!!!!!!!!!!!!!!

:d :d :d :d :d :d :d :d :d :d
Reply 676
Avatar for susan23
susan23
3
How do you do this?

a sample of 5 x 10^20 atoms of plutonium-239 and 40^20 atoms of plutonium-240.

State the half life of plu-239>?
Reply 677
Avatar for sulexk
sulexk
OP
11
Original post by jamedz
here's a bit of bed time reading for you :wink: it's a few summaries of just about every long answer question they could ask.. don't know how I've manged to do all this today :P its like half an EPQ.. ah well it should hopefully be worth it :tongue: enjoy :biggrin:


Quality!
Reply 678
Avatar for jam.wa
jam.wa
8
Original post by susan23

Original post by susan23
How do you do this?

a sample of 5 x 10^20 atoms of plutonium-239 and 40^20 atoms of plutonium-240.

State the half life of plu-239&gt;?


Surely more information needed?
Reply 679
Avatar for Ralphus J
Ralphus J
I really dont think MRI procedure will come up as it was the BIG marker last year and the formation AND evolution of a star was febuarys.

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