OCR A2 Physics A: G484 &amp; G485 - 15 &amp; 21 Jun 2017 [Exam Discussion]

Original post by headyb

Tad lengthy.
Ir/Io=0.4 (as 40% reflected) Using Ir/Io=(Z2-Z1)^2/(Z2+Z1)2, I squared both sides and rearrange to make Z2 the subject and enter value for Z1 (1.7x10^6).

Also, I think the energy used to kill cancer cells = 1.3J

same, was annoying to write out, got a diff value than you for density though, did you just do Z(muscle)/1600?

Reply 122

Original post by sadasdasdasd

same, was annoying to write out, got a diff value than you for density though, did you just do Z(muscle)/1600?

Wasn't it asking calculate the density of the bone? I did Z(bone)/1600

Reply 123

Original post by headyb

Wasn't it asking calculate the density of the bone? I did Z(bone)/1600

it was on the previous page to the bone question, had to turn over to get to the bone one from the muscle one

Reply 124

Original post by sadasdasdasd

it was on the previous page to the bone question, had to turn over to get to the bone one from the muscle one

Oh slight memory lapse! Yeah I did 1.7x10^6/1600=1062.5 and rounded to 1063

Reply 125

there was the power transferred by x-ray question and then mass change of the star (1.8*mass of sun).
power transfer I used the exponential formula to find I, did I*A (had to multiply mm^2 by 10^-6 to get m^2) then multiplied this by 2*60.
mass of the star was just an energy calculation followed by using E=mc^2
ratio was something like 0.33, dunno

Reply 126

advantages for MRI over CAT I wrote that MRI is non-ionising as no x-rays and that CAT scans provide better contrast for soft tissues (with low Z).

Reply 127

Original post by sadasdasdasd

there was the power transferred by x-ray question and then mass change of the star (1.8*mass of sun).
power transfer I used the exponential formula to find I, did I*A (had to multiply mm^2 by 10^-6 to get m^2) then multiplied this by 2*60.
mass of the star was just an energy calculation followed by using E=mc^2
ratio was something like 0.33, dunno

I think the energy used to kill the cancer cells was 1.3J (A=6mm2 ,x=1.4?cm, I=2x10^6, u=5cm, t=120s). I worked out the intensity then multiplied by area for power, then time for energy.

Can you remember if it stated 2pm in the X-ray production question? I might have been 20pm actually..

(edited 6 years ago)

Reply 128

Original post by headyb

I think the energy used to kill the cancer cells was 1.3J (A=6mm2 ,x=1.4?cm, I=2x10^6, u=5cm, t=120s)

Can you remember if it stated 2pm in the X-ray production question?

was 12pm, got 23j for the energy question though.
it gave a huge value for voltage for me anyway, 6.xx*10^something

Reply 129

adsy9

1

Original post by headyb

I think the energy used to kill the cancer cells was 1.3J (A=6mm2 ,x=1.4?cm, I=2x10^6, u=5cm, t=120s). I worked out the intensity then multiplied by area for power, then time for energy.

Can you remember if it stated 2pm in the X-ray production question? I might have been 20pm actually..

it was 2pm

Reply 130

Original post by sadasdasdasd

was 12pm, got 23j for the energy question though.
it gave a huge value for voltage for me anyway, 6.xx*10^something

Yeah I ended up with a value just under 7x10^5 I think, rounded up due to the question asking for producing a minimum wavelength X-ray of 2pm.

Reply 131

WilliamGates

Original post by emmabrindley1

This is my attempt at uploading it ??? Not sure if it worked

Thank you for your effort, didn't see it in time though - paper was easy enough. Magnetic resonance+sun evolution free marks..

Reply 132

Original post by adsy9

it was 2pm

I thought it was about that. I ended up using 10-13 by some weird mistake for the pico meter though.

Reply 133

Magnetic field:
Momentum of particle=3.456x10-23
Energy=4102eV
Time for 60deg=(1/6)(2pi)(0.018)/(v)=4.96x10-10s

Radioactivity:
Ra-222 -> Po-218 + alpha particle.
Number of radioactive isotopes in the basement=1.80x10^7
Ratio of isotopes to 40mol of air=7.46x10^-19.
Emits harmful ionising radiation and has a long half life.

Reply 134

Original post by headyb

Magnetic field:
Momentum of particle=3.456x10-23
Energy=4102eV
Time for 60deg=(1/6)(2pi)(0.018)/(v)=4.96x10-10s

Radioactivity:
Ra-222 -> Po-218 + alpha particle.
Number of radioactive isotopes in the basement=1.80x10^7
Ratio of isotopes to 40mol of air=7.46x10^-19.
Emits harmful ionising radiation and has a long half life.

what was your particle velocity?
lambda for the decay was something like 0.693/3days, 40/this was 2.xxx

Reply 135