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June 2011 G485-Fields, Particles and Frontiers of Physics

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Reply 480

MarieLyon

And the specimen paper is totally useless! They dont even give questions like that in the past papers.

Reply 481

MarieLyon

Original post by johndory13

You do not need the know the differences because they are completely different one uses X rays and the other gamma
And there are very few similarities

more likely to compare similar radiation

oh I know they wouldnt ask for similarites/differences in a question. I was just askig generally.

Reply 482

M_I

Original post by Oh my Ms. Coffey

Explain Compton Scattering and the Photoelectric effect.

Photoelectric effect - a photon with about 30keV of energy hits and electron in the tungsten atom, the electron is ejected, another electron fills the gap in the lower energy level shell, releasing a photon

Compton Scattering - a photon with about 0.5 - 5 MeV of energy hits an electron and knock it out, photon loses energy and is scattered.

Would I need to add any more info?

--------------------------------------------------------

How do radiographers try to produce a sharp image while minimising the radiation dose?

Reply 483

TobeTheHero

i ****in love this unit2 :biggrin:

so many interesting concepts

Reply 484

Nirgilis

This may sound ridiculous, but what's the difference between potential difference and voltage? :colondollar:

Reply 485

mrpope1000000

Hey can someone please clarify if we need to know the moons of planets in the solar system?
The specification's a bit vague... it just says 'describe in terms of planetary satellites'. :s-smilie:

Reply 486

M_I

Original post by Kidms001

This may sound ridiculous, but what's the difference between potential difference and voltage? :colondollar:

There's a difference?

Reply 487

M_I

Can someone re-explain A-Scan and B-Scan?

Reply 488

trapzbrah

Original post by TobeTheHero

i ****in love this unit2 :biggrin:

so many interesting concepts

Reply 489

MarieLyon

Original post by M_I

Can someone re-explain A-Scan and B-Scan?

Pulses of ultrasound are sent into the body, the signal is reflected. The time of delay is used to calculate the depth. The refraction of reflection is used to identify the tissue. A-scan is just one of these. B-scan is many of these producing a better image.

(edited 12 years ago)

Reply 490

scotzbhoy

Original post by MarieLyon

I think we are going to get a long question on x-rays or the gamma camera because Jan 2011 asked for MRI and Jun 2010 asked for ultrsound.

Can someone give me any information on PET and CAT (like the differences between them). :smile:

X-rays came up in June '10

Reply 491

mrpope1000000

Original post by M_I

Can someone re-explain A-Scan and B-Scan?

A-scan (amplitude scan) shows reflections as vertical deflections on the CRO screen, like a wiggly horizontal line, indicating the time the echo took to return - so you can calculate distances.

B-scan (brightness scan) shows up as dots of varying brightness. Larger amplitude of reflected waves = brighter spot. You can build a 2-d image with this but not with A-scan.

Hope this helps :smile:

Reply 492

MarieLyon

Original post by scotzbhoy

X-rays came up in June '10

onlt the contrast media and intensifiers nothing to do with compton scattering... photoelctric effect and that positron one.

Reply 493

M_I

Original post by MarieLyon

Oh ok, I think I'm seeing how it works now.

What do we need to know about the mass attenuation coeffecient?

Reply 494

PhilliChilli

Original post by PpphelannN

This goes into a big more detail than we need to know, but hey :smile:

I got it from this http://www.thestudentroom.co.uk/attachment.php?attachmentid=101328&d=1305275576
It's well sick :smile:

Also these might help :biggrin:

Hope this helps, the pdf is useful as well it highlights like keywords and stuff :smile:

It's good cos our book (the pizza one) is useless for that kinda thing :/

Thank you ! :smile:

(Jack...?) Ill definately be reading over this tonight! Good luck for tomorow!

Reply 495

MarieLyon

Original post by M_I

Oh ok, I think I'm seeing how it works now.

What do we need to know about the mass attenuation coeffecient?

there's an equation for it isn't there? And that isn't ultrasounds its x-rays. isn't it?

Reply 496

jam.wa

Hubble, with your stupid units for your stupid constant.

Why couldn't you always just leave it as s^-1?

Oh, you wanted loads of A-level candidates to waste time doing stupid 1 markers dividing km s^-1 by M Pc^-1?

Go AWAY.

Reply 497

M_I

Original post by mrpope1000000

Making more sense everytime I read something about it.....i hate Ultrasound.

Reply 498

susan23

ok what answer do you get for this for the total capacitance...show ur working.

(edited 12 years ago)

Reply 499

muffingg

In a simple photographic flashgun a 0.20F capacitor is charged by a 9.0V battery. It is then discharged in a flash of duration 0.01s. Calculate the approximate resistance of the bulb.

How do you do that?

Answer in spoiler.

Spoiler

Edit- I'm not trying to test anyone or anything. I'm just confused how to get to that answer because my book says this is the answer to the question. I keep getting a different value than that.