VCE Physics Question Thread!

[saifh]

Can I stick stuff on my cheat sheet using tape?

[Infinity Plus]

definitely noticeable diffraction at 1 but vcaa will either give you something obviously small like 0.000001 if theres no diffraction

Thank you man!

[Robert123]

For light and matter, do we need to know the required voltage to accelerate an electron? I have been given heaps of question related to it in private companies exams (particularly atar notes) but not VCAA

[Alwin]

For light and matter, do we need to know the required voltage to accelerate an electron? I have been given heaps of question related to it in private companies exams (particularly atar notes) but not VCAA

It's not hard... but I'm pretty sure that that sounds like a detail study (synchrotron irrc) question not a core studies question...

Pretty sure it's not something you need to know.

[lzxnl]

For light and matter, do we need to know the required voltage to accelerate an electron? I have been given heaps of question related to it in private companies exams (particularly atar notes) but not VCAA

The definition of voltage is the potential energy difference per charge. So, a 1 V potential energy difference would give a 1 C charge 1 J of energy. Use E=Vq if you ever come across it.

It's not hard... but I'm pretty sure that that sounds like a detail study (synchrotron irrc) question not a core studies question...

Pretty sure it's not something you need to know.

Technically, in the photoelectric effect, if you have electron energy=hf-W, then the stopping voltage would be 1/q*(hf-W) which explains the gradient of the curve. It's not entirely out of the course.

[Alwin]

The definition of voltage is the potential energy difference per charge. So, a 1 V potential energy difference would give a 1 C charge 1 J of energy. Use E=Vq if you ever come across it.

Technically, in the photoelectric effect, if you have electron energy=hf-W, then the stopping voltage would be 1/q*(hf-W) which explains the gradient of the curve. It's not entirely out of the course.

k

coz last year when I asked about this (forces on charged particles) my teacher said it wasn't strictly on the course. Who knows, maybe this could be your lucky year guys XD

[jono88]

-Identify rms voltage as an AC voltage which produces the same power in a resistive component as a DC voltage of the same magnitude
-explain the production of atomic absorption and emission spectra, including those from metal vapours?

I don't understand these 2 dot points, could someone elaborate further?

[jono88]

Spectra
The electromagnetic radiation that is emitted from a free atom only occurs at a number of discrete or separate wavelengths or frequencies.  This is usually represented as a set of lines.
Visible spectrum of hydrogen spectrum

Interpretation of Spectra
After Einstein, frequency is now linked to energy by E = hf.  Each line in the spectra now corresponds to a transition of an electron from one energy level to another level.

In fact, the discrete lines in the spectra must mean that electrons in atoms can only exist at specific energy levels, and the spectral lines represent transitions between these levels.

When an atom is excited electrons are sent to a higher energy level.  From there, the electron drops back to the ground state by any of the possible paths, each drop emitting a photon of specific energy and frequency.

That right or completely wrong?

[Robert123]

The definition of voltage is the potential energy difference per charge. So, a 1 V potential energy difference would give a 1 C charge 1 J of energy.

Thanks nilu, I understand that part it is just the random formulas out there for accelerating electrons from close to rest to form a diffraction pattern similar to x-rays, then work out what voltage is required to accelerate them. Just want to know if they are on the course?

I have a fairly good idea in deriving the formulas but if I do have to know it, it would be easier to just plug and play VCE style

[ECheong]

Thanks nilu, I understand that part it is just the random formulas out there for accelerating electrons from close to rest to form a diffraction pattern similar to x-rays, then work out what voltage is required to accelerate them. Just want to know if they are on the course?

I have a fairly good idea in deriving the formulas but if I do have to know it, it would be easier to just plug and play VCE style

If you consider the electronvolt (eV), 1 eV is the amount of energy you get when you accelerate an electron through a potential difference of 1 volt. So, I guess what you can do is find the energy the electron has in eV, and then you can find the potential difference it was accelerated through.

Re: X-rays, you'd just need to find the velocity at which the electrons have a debroglie wavelength the same as xrays and then use E=0.5mv^2 to find energy, convert to eV and you'll know the potential that electron was accelerated through

[Alwin]

-Identify rms voltage as an AC voltage which produces the same power in a resistive component as a DC voltage of the same magnitude
-explain the production of atomic absorption and emission spectra, including those from metal vapours?

I don't understand these 2 dot points, could someone elaborate further?

RMS: V_p indicates the voltage peak of an AC voltage vs power graph. Basically:

It works on the prinicple the power output should be the same, but that's based on a perfect sine graph. Here's a generic proof if you were interested
http://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-a-sine-wave-with-a-dc-offset/

Absorption and emission in physics is pretty straight forward, specific/discrete/quantum (if you want to be fancy) amount of energy needed to excite electrons to a higher state, and they release this energy when they fall back to a lower state.
Most calculations in physics involve finding the energy in eV, wavelength of photon emitted and whether a photon of another different energy will have any impact on the atom in question.

Note that electron absorption is not on the course... but fun to read about

[iitwinz]

hey guys, did we have to know the skin effect and optical fibres and how they work? I don't remember learning about it at all and haven't seen any on the exam.

[Alwin]

hey guys, did we have to know the skin effect and optical fibres and how they work? I don't remember learning about it at all and haven't seen any on the exam.

It's been put into one of the detailed studies not in the core section of the exam

[iitwinz]

It's been put into one of the detailed studies not in the core section of the exam

cool thanks man

[Lachjames]

Hi guys, on the 2011 Exam 2 Electric Power Q.11, I've been talking with my friend from school and we can't figure the graph out. We looked at the VCAA solution and we get what they're saying but we were thinking something else - I put our train of thought in the attachment below.

Pretty much it's that since the flux will reduce once the magnet is actually inside the loop shouldn't that cause some emf generation, spiking in the opposite direction? The attachment will make what I'm saying clearer hopefully (even if it is nonsense lol)

Any advice would be great, thanks