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GCSE Physics P3 - 24/05/2012

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Reply 20
Original post by Melissajanex
Please could someone explain what an ECG is? I've seen it crop up in past papers but don't understand. Thanks :smile:


It's basically a machine used to measure action potentials in the heart. Here is how I remember how it works:

1. The heart is a pump made of muscle; it has 4 chambers, 2 atria which are at the top and 2 ventricles which are below.
2. When the heart beats, an action potential passes through the 2 atria at the top, making them contract. A moment later the same happens with the ventricles.
3. Once the action potential passes, the muscles contract.
4. The action potentials produce weak electrical signals on the skin which can be detected by electrodes attached to the arms, legs and chest.

I've also seen the graph come up on a couple of papers, and you need to be able to describe it:

http://media-1.web.britannica.com/eb-media/95/26995-004-E5839E67.gif

- The 'P' wave is when the atria contract
- The 'QRS' wave is when the ventricles contract
- The 'T' wave is the recovery wave

Hope this helps :smile:
Reply 21
Original post by lettucesoap
nearly there - m = mass and v = velocity

so momentum = mass / velocity


I think it is mass x velocity, that's what it says when i look it up on google. Sorry if i'm wrong.

Btw how do you suggest i revise for all the weird questions that come up? in the past papers it seems like theres so many questions that aren't in the cgp book that i couldn't have revised for.
(edited 11 years ago)
Original post by hypanx
I think it is mass x velocity, that's what it says when i look it up on google. Sorry if i'm wrong.

Btw how do you suggest i revise for all the weird questions that come up? in the past papers it seems like theres so many questions that aren't in the cgp book that i couldn't have revised for.

That's what I found whilst doing past papers, they're usually only 1 or 2 marks but every mark counts!
Reply 23
Original post by Melissajanex
That's what I found whilst doing past papers, they're usually only 1 or 2 marks but every mark counts!


I know, i revisedit and it seemed easy then when i came to doing papers i barely knew any of the answers :frown:
Original post by hypanx
I know, i revisedit and it seemed easy then when i came to doing papers i barely knew any of the answers :frown:


Hopefully it will be much easier this year! The chemistry and biology weren't so bad
Reply 25
URGENT QUESTION- PLEAS HELP!

On a few of the past papers I have noticed that it give you like. List of radioactive emitters eg. Technetium 99 and asks you to choose the best one for a tracer and treatment. What type of radiation eg. Gamma/alpha/beta is best for these?
Reply 26
Original post by IsabelAmy
URGENT QUESTION- PLEAS HELP!

On a few of the past papers I have noticed that it give you like. List of radioactive emitters eg. Technetium 99 and asks you to choose the best one for a tracer and treatment. What type of radiation eg. Gamma/alpha/beta is best for these?


Gamma. Its half life should be around 6 hours.
Reply 27
Original post by hypanx
Gamma. Its half life should be around 6 hours.


Is that for the tracer and treatement?
Reply 28
Original post by IsabelAmy
Is that for the tracer and treatement?


Gamma is used in both but i'm not sure about the half lives, they may be different. For treatment it depends on what kind i think, i'd just choose the half life which is around 6 hours though.

Are you finding the P1xV1/T1 = P2xV2/T1 questions difficult when you have to reaarange them?
Reply 29
Thank you for you help.
I'm finding them okay because I do additional maths. Just remember that the temperatures are in kelvin :smile:
Original post by taliaa
It's basically a machine used to measure action potentials in the heart. Here is how I remember how it works:

1. The heart is a pump made of muscle; it has 4 chambers, 2 atria which are at the top and 2 ventricles which are below.
2. When the heart beats, an action potential passes through the 2 atria at the top, making them contract. A moment later the same happens with the ventricles.
3. Once the action potential passes, the muscles contract.
4. The action potentials produce weak electrical signals on the skin which can be detected by electrodes attached to the arms, legs and chest.

I've also seen the graph come up on a couple of papers, and you need to be able to describe it:

http://media-1.web.britannica.com/eb-media/95/26995-004-E5839E67.gif

- The 'P' wave is when the atria contract
- The 'QRS' wave is when the ventricles contract
- The 'T' wave is the recovery wave

Hope this helps :smile:

Thankyou so much!:smile:
Reply 31
Guys its almost 1am and im still revising, i hope the tomorrow exams go well.
Reply 32
Remember

the tracer (radiopharmaceutical) - uses a short half-life usually Fluorine-18 (has a half-life of 110 mins) is used.

treatment - uses a longer half-life with a higher energy emitted and it needs to have good penetration, so gamma radiation is used and treatment is taken over a period of consecutive days.
(edited 11 years ago)
Original post by Melissajanex
Please could someone explain what an ECG is? I've seen it crop up in past papers but don't understand. Thanks :smile:


electrocardiograph.
http://img.tfd.com/vet/thumbs/gr141.gif
its the graph that displays the electrical activity in the heart.
it's got 5 'blips' named P,Q,R,S, and T
You know how the heart has two nodes that create a wave of depolarisation? the first blip shows the top half of the heart (the atria)'s wave of depolarisation and how the muscle cells contract, pushing the blood into the bottom half (the ventricles)

you'll notice on the typical electro cardiograph that after the first blip that there is a tiny straight line where the charge of the heart returns to normal.
this is the sino atrial node delaying the second wave of depolarisation.

thirdly, you'll see a huge spike in the electrocardiograph. this is the the VENTRICLE contracting & having it's wave of depolarisation in the muscle cells.

the fourth mini blip is the ventricle returning to normal.

common questions I've seen to do with ECGs are comparing two people's ECGs. One may have a person's ECG which is really fast. they're probably exercising - how do we know this? well the heart needs to pump more oxygenated blood & therefore the whole contracting process is more common
the same goes for a ECG with fless common blips of PQRST - they're probably resting, because your heart doesnt do much when resting.

another type of ECG they could give us is an irregular one, or one that's missing one of the blips. This shows that they have a heart problem and should probably get that $h1t checked out.
Original post by hypanx
I think it is mass x velocity, that's what it says when i look it up on google. Sorry if i'm wrong.


oh yeah you are right, sorry my mistake.:colondollar:
Can someone please explain the inverse square law in relation to intensity? :confused:
Reply 36
How did you guys find the exam? Can we map out the answers?

for the kinetic energy one did you guys put a minus in front of it?
Reply 37
2008 exams were the easiest i think these were also quite hard.
Reply 38
Guys - can everyone say all the answers they got, so we can put an 'unoffical mark scheme together'

I remember getting 'Action Potential' for the x axis question
4.25 x 10(to the -18) .. i think
293Kelvin
Reply 39
actually i think i got 290 for the Kelvin question..

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