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

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Oh god
i need an a in this to get into ucl arghhhhhhhhhhhhhhhhhhhhhhhh
Original post by ChiefKeef
Oh god
i need an a in this to get into ucl arghhhhhhhhhhhhhhhhhhhhhhhh


In the same situation here :frown::frown::frown: T.T
Original post by ChiefKeef
Oh god
i need an a in this to get into ucl arghhhhhhhhhhhhhhhhhhhhhhhh


I'm not going to uni so I'm not really concerned about that. But let me tell you something; revise now, even one hour makes a difference, the hour that you learn something you didn't know, even that hour before the exam. Trust me


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So I've gone and revised every topic and done all the old paper as well as the new ones. What do people suggest me do now? Shall I just repeat all the old papers again and make sure im 100% on everything that didn't come up last year


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Reply 1784
Now that there's a replacement paper I wouldn't bank on the "it came up last year so won't come up again" method guys.
Original post by CD223
Now that there's a replacement paper I wouldn't bank on the "it came up last year so won't come up again" method guys.


That's true! Although I think it's likely some stuff that came up last year will come up again, there's only so much they can ask after all. Especially in the astrophysics topic
Original post by sam_97
That's true! Although I think it's likely some stuff that came up last year will come up again, there's only so much they can ask after all. Especially in the astrophysics topic


Famous last words
Reply 1787
Original post by sam_97
That's true! Although I think it's likely some stuff that came up last year will come up again, there's only so much they can ask after all. Especially in the astrophysics topic


In Astro I suppose yes, although you'll always have classic diagrams, HR graphs and calculations!


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Could anyone explain STM microscopes even after reading about them can't seem to understand??


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What synoptic stuff is there from as?
Any Feynman diagrams?
What equations do we need to know for unit 5 that are not given on the data sheet?


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Original post by Jimmy20002012
Could anyone explain STM microscopes even after reading about them can't seem to understand??


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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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Original post by louisg565
What equations do we need to know for unit 5 that are not given on the data sheet?


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great question, needed this for PHYA4 tbh, but does anyone have a list of useful equations we might need?
Wish I didn't have c4 today, just want to get on with physics revision :frown:(


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How do u calculate the energy released in an alpha decay equation ?
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 :biggrin: this helps a lot, is this all we need to know? :smile:


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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
Original post by Jimmy20002012
Thanks so much :biggrin: this helps a lot, is this all we need to know? :smile:


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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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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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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.

ImageUploadedByStudent Room1434453829.619802.jpg


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