HSC Physics Question Thread

[FallonXay]

Hihi! In regards to the Braggs' Diffraction Experiment, why did they specifically use X-rays as opposed to other forms of EMR?

[jamonwindeyer]

Hihi! In regards to the Braggs' Diffraction Experiment, why did they specifically use X-rays as opposed to other forms of EMR?

Hey FallonXay!! The reason is simply because the wavelength of an X-ray is very similar to the average spacing between atoms in a metallic crystal lattice, thus maximising the effects of scattering and creating a more accentuated diffraction pattern  I know this principle has a name, but it eludes me, and the specifics of it are beyond the syllabus anyway 

[jakesilove]

Hey FallonXay!! The reason is simply because the wavelength of an X-ray is very similar to the average spacing between atoms in a metallic crystal lattice, thus maximising the effects of scattering and creating a more accentuated diffraction pattern  I know this principle has a name, but it eludes me, and the specifics of it are beyond the syllabus anyway 

Yep, can confirm Jamon's answer having just recently done exactly this experiment! We fired x-rays into Sodium and Potassium, and used the fact that the wavelength was similar to the spacing to do crazy calculations. Principle-wise, we just used basic x-ray diffraction and various iterations of Braggs law Maybe some Compton shift stuff in there as well, but again this is well beyond the syllabus! For that matter, you hardly need to know anything about these experiments for the HSC; hardly ever assessed, barely even taught.

Jake

[jamonwindeyer]

Yep, can confirm Jamon's answer having just recently done exactly this experiment! We fired x-rays into Sodium and Potassium, and used the fact that the wavelength was similar to the spacing to do crazy calculations. Principle-wise, we just used basic x-ray diffraction and various iterations of Braggs law Maybe some Compton shift stuff in there as well, but again this is well beyond the syllabus! For that matter, you hardly need to know anything about these experiments for the HSC; hardly ever assessed, barely even taught.

Jake

Oh that is so cool. My experiments in Electrical are restricted to dodgy circuits on breadboards 

[jakesilove]

Oh that is so cool. My experiments in Electrical are restricted to dodgy circuits on breadboards 

Oh don't worry; next year I get to use a pendulum to find an approximation for Gravity again, so I have plenty of shit pracs to look forward to!

[Neutron]

Hey hey!

Been a while again, but I have a research assignment on Q2Q and I'm having some trouble with one of the questions and i was wondering whether you amazing genuises could shed some light?

"Explain how the rate of fission is controlled in a nuclear reactor and how adjustments are made over the lifetime of the fuel rods."

It's only the underlined part that I'm having trouble with and if you guys have could please help a gal out that would be great! Thank you!

Neutron

[jakesilove]

Hey hey!

Been a while again, but I have a research assignment on Q2Q and I'm having some trouble with one of the questions and i was wondering whether you amazing genuises could shed some light?

"Explain how the rate of fission is controlled in a nuclear reactor and how adjustments are made over the lifetime of the fuel rods."

It's only the underlined part that I'm having trouble with and if you guys have could please help a gal out that would be great! Thank you!

Neutron

Hey Neutron!

I didn't do Q2Q myself, and haven't studied this area of physics at university, so nothing special to offer you. I did some research, and the link here has a paragraph about turning on and off the rods in order to adjust for changes in the rate of fission (to ensure a critical yield etc.). All other research (eg here) seems to support this idea; that Fuel rods are basically turned 'on and off' in order to stabalise the rate of reaction.

Hope that helps! Hopefully someone on here did Q2Q and can help out a little more!

Jake

[znaser]

Hi. I'm just asking in regards to the formation of electron-hole pairs in extrinsic semi-conductors. So I understand that it is the movement of the positive holes in the valence band that constitutes current but I am confused as to whether there are movement of electrons in the conduction band. I'm also confused about the production of electron-hole pairs in an intrinsic semi-conductor. Is it that the electrons move from the valence band to the conduction band (when exposed to a high energy source) and leave behind a hole in the valence band and the process just continues or does it mean something else? Thanks in advance

[jamonwindeyer]

Hi. I'm just asking in regards to the formation of electron-hole pairs in extrinsic semi-conductors. So I understand that it is the movement of the positive holes in the valence band that constitutes current but I am confused as to whether there are movement of electrons in the conduction band.

Hey there!! So that's a pretty tricky question to answer, but essentially, no. However, remember that the holes moving in the valence band means that there will also be electrons moving in the valence band, in opposite directions! You might understand why this is already, but if not let me know!!

Now, this doesn't mean that there won't be some electrons moving in the conduction band. However, we call holes the majority charge carriers, because the majority of the charge movement is due to the hole movement in the valence band.

And just confirming, this covers the p-type extrinsic case. Is this what you were after? 

I'm also confused about the production of electron-hole pairs in an intrinsic semi-conductor. Is it that the electrons move from the valence band to the conduction band (when exposed to a high energy source) and leave behind a hole in the valence band and the process just continues or does it mean something else? Thanks in advance

Okay, so basically you've got the idea. Electrons graduate from the valence band to the conduction band via some external energy source (like a voltage), and yes. This leaves a hole in the valence band. Then these carry charge in the valence band. So in intrinsic semiconductors, we have a combination of conduction electrons and valence holes carrying charge for us. It is only when we dope the semiconductor that one starts to dominate over the other 

I hope this helps!! I'm happy to clarify if necessary 

[znaser]

Yep that's exactly what I'm after. Thank you that rlly helps! 

[jamonwindeyer]

Yep that's exactly what I'm after. Thank you that rlly helps! 

Awesome! No worries at all 

[conic curve]

Is this for prelim physics or HSC physics?

[Ahsun]

At one time it was proposed to launch satellites directly into a circular orbit at a constant distance from the Earth using a giant WW2 cannon. Assuming that the cannon would give the satellite a largely sufficient velocity, explain and use calculation to show why this proposal would not work ?
I just need a guide on what i need to do i was thinking something to do with newtons thought expirements but not sure about the calculation part.

[Swagadaktal]

hey can someone link me the hsc physics study design (or equivalent thing?)

Physics here seems so interesting in comparison to vce physics.
if i didnt have an amazing teacher i dont think id be enjoying physics as much as i do atm but based off the questions in the hsc physics you guys seem like you're having a blast. some really fascinating ideas

[jamonwindeyer]

Is this for prelim physics or HSC physics?

Both! We even have some inter-state students asking questions (which we answer with some success), so ask away!