VCE Physics Question Thread!

[zsteve]

Also, is it possible for an electron to de-excite from level - I don't think so, but just confirming?

[lzxnl]

Also, is it possible for an electron to de-excite from level - I don't think so, but just confirming?

That's basically capturing an electron by a cation, and yes that happens.
If you somehow managed to make He+, like in a mass spectrometer, you'd reform neutral He pretty easily.

[Adequace]

Since in terminal velocity, mg = air resistance so Fnet=0, this means that there's no direction right? I'm confused since in checkpoints' answers it has an arrow pointing upwards.

[zsteve]

The arrow might be the air resistance force, not net force? Otherwise possibly an error.

[Adequace]

The arrow might be the air resistance force, not net force? Otherwise possibly an error.

Ah, appears like it. Cheers.

[paper-back]

On the VCAA exam do we need to draw the gradient version of the flux graph for EMF when told to draw the graph for EMF, E.g. sine flux -> cosine EMF
Or do we just leave it as a sine graph, regardless of whether the flux graph is sine or cosine?

[zsteve]

You need to follow the rate of change. This means a sine graph -> negative cosine graph due to Lenz's law [Negative due to Lenz's law, cosine due to Faraday's. Thanks |zxn| ]. You can simply read points and gradients off the graph and draw out the graph.

[lzxnl]

You need to follow the rate of change. This means a sine graph -> negative cosine graph due to Lenz's law. You can simply read points and gradients off the graph and draw out the graph.

To be honest, I don't even know if VCAA expects you to know that a + sine flux graph gives you a - cosine EMF graph (that isn't Lenz's law; that's Faraday's law of induction). I mean, they get you to count squares to work out gravitational potential energy changes so they clearly don't expect knowledge of rudimentary calculus.

[Floatzel98]

Me and a friend were trying to calculate how fast a person would have to travel to be able to 'diffract' through a door. We took the width of a door to be 1m. For diffraction to be observable(?) the wavelength / slit width has to be approximately 1 (). So to find the velocity of a 60kg person to produce a wavelength of approx 1m we went



m/s

We have probably (obviously) made some assumptions that don't make sense (maybe we just haven't understood the course properly yet). We just don't understand why it is such a small speed. Is this all incorrect because a single person can't be treated as single particle (point of mass)? We only did this for fun, but I'm confused about our answer and what it means exactly / why it doesn't make sense.

Also, when doing a double slit experiment, why doesn't air effect any part of the experiment. The light obviously still has to pass through air, so why doesn't this effect the interference pattern at all? Is it just because of the relative size of light compared to these atoms/molecules? 

Another thing, I know I've only been doing real physics (that's probably a stretch for VCE) for two years now, but I honestly don't feel I can explain anything that happens in the real world. Like I can't seem to ever really apply any of what I've learn't to real life scenarios. Is this normal? I know I can't expect much out of VCE, but do you actually end up 'learning' things when you get to university?

Thanks guys, any help would be appreciated

[lzxnl]

Me and a friend were trying to calculate how fast a person would have to travel to be able to 'diffract' through a door. We took the width of a door to be 1m. For diffraction to be observable(?) the wavelength / slit width has to be approximately 1 (). So to find the velocity of a 60kg person to produce a wavelength of approx 1m we went



m/s

We have probably (obviously) made some assumptions that don't make sense (maybe we just haven't understood the course properly yet). We just don't understand why it is such a small speed. Is this all incorrect because a single person can't be treated as single particle (point of mass)? We only did this for fun, but I'm confused about our answer and what it means exactly / why it doesn't make sense.

Also, when doing a double slit experiment, why doesn't air effect any part of the experiment. The light obviously still has to pass through air, so why doesn't this effect the interference pattern at all? Is it just because of the relative size of light compared to these atoms/molecules? 

Another thing, I know I've only been doing real physics (that's probably a stretch for VCE) for two years now, but I honestly don't feel I can explain anything that happens in the real world. Like I can't seem to ever really apply any of what I've learn't to real life scenarios. Is this normal? I know I can't expect much out of VCE, but do you actually end up 'learning' things when you get to university?

Thanks guys, any help would be appreciated

Actually what you've done looks fine to me. It's such a tiny speed because we're such large objects. Diffraction essentially means there's a macroscopic uncertainty in where your position is. Use Heisenberg's uncertainty principle and you'll find that the uncertainty in momentum required for a person to have a positional uncertainty of 1 m is tiny.

Past VCE, you'll find that VCE physics was absolutely nothing compared to what's out there in uni. Then, when you leave uni, you find that what you did in uni was nothing compared to the real world.

You do learn things at uni; it's just that you learn fundamentals at uni that you'd have to try and then apply in real life. You can't apply VCE stuff to real life because...high school sucks, full stop. There's only so much stuff you CAN learn in two years of high school with such a limited background. Plus, remember high school curricula have to accommodate for all types of students, so incredibly fast-paced accelerated courses aren't allowed.

[Orson]

Hey everyone...I was wondering what kind of stuff you are all putting on your cheat sheets...would I need definitions for Work function and stuff? (I remember this coming on an exam, but can't remember if it was VCAA or not...

[odeaa]

Hey everyone...I was wondering what kind of stuff you are all putting on your cheat sheets...would I need definitions for Work function and stuff? (I remember this coming on an exam, but can't remember if it was VCAA or not...

I'm just putting equations, if you have too much theory you won't think intuitively and will just copy down irrelevant answers (well that's my theory)

[Adequace]

I'm just putting equations, if you have too much theory you won't think intuitively and will just copy down irrelevant answers (well that's my theory)

Isnt there an equation sheet attached to the exam?

[odeaa]

Isnt there an equation sheet attached to the exam?

Yeah but it's useless as it only has the basics

In 3/4 there a quite a few 'shortcut' formulas that aren't even really shortcuts because literally everyone uses them, you'd probably struggle to finish the exam if you derived all your formulas from their sheet
Also it's nice to have them laid out in a specific format

[Adequace]

Yeah but it's useless as it only has the basics

In 3/4 there a quite a few 'shortcut' formulas that aren't even really shortcuts because literally everyone uses them, you'd probably struggle to finish the exam if you derived all your formulas from their sheet
Also it's nice to have them laid out in a specific format

Ah, yeah true.

Would assssors care if you just use sqrt(height/5) to find the time in projectile questions? I've heard people say it's not a 'valid' formula to use in the end of year exam.