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# AQA Physics PHYA5 - Thursday 18th June 2015 [Exam Discussion Thread] watch

1. How do u calculate the energy released in an alpha decay equation ?
2. (Original post by gcsestuff)
I'll give it a go.

The stm microscope is an example of particles (electrons) exhibiting wave like properties. If the gap between the positive plate where the source is placed and the negative tip from where the electrons are released is small enough then electrons can "jump' from the negative tip to the positive plate. The PD across the plates has to be significant enough so that electrons are attracted and they only pass in one direction. If the gap is to wide then transmission will not occur. This is how electrons 'tunnel' across the gap.

That's the concept on how it works.

There are two types of stm microscope.

1 - constant current mode . The fine tip has its height change so that the current on the positive plate is always the same. If the souce gets thicker the tip is moved up and if it gets thinner the tip is moved down. The tip is never more than 1nano metre from the source. The height of the tip is then compared with time and a image can be produced.

2- constant height mode. The tip scans across the source and its gap width varies. This created changing currents on the positive-plate. Current decreases with gap width. Variation of current and time is then used to map out the surface. Again it's never more than 1 nm from the surface.

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Thanks so much this helps a lot, is this all we need to know?

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3. (Original post by CD223)
In Astro I suppose yes, although you'll always have classic diagrams, HR graphs and calculations!

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Exactly! They do seem to like their Hertzsprung-Russell diagrams and black body radiation curves
4. (Original post by Jimmy20002012)
Thanks so much this helps a lot, is this all we need to know?

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I've done all the past papers and they have never wanted anything more. I think stuff like how the image is formed Is to advanced to go into detail

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5. I'm a bit confused;

Can someone explain the different sizes of particles effects neutrons.

So in the control rod neutrons need to be absorbed so does that mean the particles inside the rods are similar sizes or smaller?

Same for the moderator, that needs to withdraw ke from the neutrons, does this mean the moderator has similar sized particles so that elastic collisions can take place and the ke be reduced?

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6. (Original post by gcsestuff)
I've done all the past papers and they have never wanted anything more. I think stuff like how the image is formed Is to advanced to go into detail

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Thanks! Do we need to know how to calculate specific charge using this method, as it is not even in the spec I don't think.

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7. (Original post by gcsestuff)
I'm a bit confused;

Can someone explain the different sizes of particles effects neutrons.

So in the control rod neutrons need to be absorbed so does that mean the particles inside the rods are similar sizes or smaller?

Same for the moderator, that needs to withdraw ke from the neutrons, does this mean the moderator has similar sized particles so that elastic collisions can take place and the ke be reduced?

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The control rods simply need to absorb neutrons so, according to Wikipedia...

"Chemical elements with a sufficiently high capture cross-section for neutrons include silver, indium and cadmium. Other elements that can be used include boron, cobalt, hafnium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.[1] Alloys or compounds of these elements may also be used, such as high-boron steel,[2] silver-indium-cadmium alloy, boron carbide, zirconium diboride, titanium diboride, hafnium diboride, gadolinium nitrate,[3]gadolinium titanate, and dysprosium titanate."

It's so that the element can absorb neutrons without going on to undergo fission itself.

Conversely, the moderator needs to be a similar size molecule so elastic collisions take place. Typically this is graphite (carbon) or water, as these dissipate the kinetic energy of neutrons to thermal levels within about 50 collisions.

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8. How much do we need to know about electron scattering to determine nuclear size?
9. (Original post by gcsestuff)
Is this the general idea of the inversion tube experiment:

Lead spheres are heated to a certain temperature.

They are then put in a tube and the tube is rotated a certain number of time.

Due to energy loss from gravity, mgh and the total no. Of rotations we can say that mcT=mghn

Which cancels to give us c= gln/T

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Which bit of the spec is this from? I don't even know it :/

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10. (Original post by 000alex)
How much do we need to know about electron scattering to determine nuclear size?
If you have a look at past six markers (I think it was 2012/2013) then there was one on alpha scattering and electron diffraction. That's the sort of detail

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11. Right, so i had an exam yesterday and beginning to panic. Im going to go though CD223s notes today and then past papers tomorrow, does this sound good?
12. (Original post by CD223)
If you have a look at past six markers (I think it was 2012/2013) then there was one on alpha scattering and electron diffraction. That's the sort of detail

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They have never really done one on the thermal physics bit so should expect that but no idea what they will ask and what you would write since that is not much theory to it!

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13. (Original post by Jimmy20002012)
They have never really done one on the thermal physics bit so should expect that but no idea what they will ask and what you would write since that is not much theory to it!

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Experiment on SHC/SLH maybe?

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14. (Original post by CD223)
Experiment on SHC/SLH maybe?

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What would we even write for that?

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15. (Original post by Jimmy20002012)
What would we even write for that?

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Apparatus, measurements, plotting of results on a graph, conclusions from graph/calculations etc. there's plenty to say.

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16. Hi everyone,

I don't study maths and therefore am not entirely sure on how to manipulate logs in a formula. Would someone who is studying astrophysics be able to post all of the variations of the formula m-M = 5log d/10 for me? It would help me out a lot
17. (Original post by ZedRigby)
Hi everyone,

I don't study maths and therefore am not entirely sure on how to manipulate logs in a formula. Would someone who is studying astrophysics be able to post all of the variations of the formula m-M = 5log d/10 for me? It would help me out a lot
Does this help?

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18. (Original post by ZedRigby)
Hi everyone,

I don't study maths and therefore am not entirely sure on how to manipulate logs in a formula. Would someone who is studying astrophysics be able to post all of the variations of the formula m-M = 5log d/10 for me? It would help me out a lot
I assume you can rearrange to make m and M the subject

Making d the subject you get:

d = 10^((m-M+5)/5)

I hope that's clear enough
19. Does anyone have a pdf file or the like which has all the unit 5 definitions you need to know in one place? Thanks
20. Do we have to know how to derive the kinetic theory model? This equation:

pV=(1/3)Nm(crms)^2

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