VCE Physics Question Thread!

[odeaa]

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.

Nah in the assessors report they often say "some students used a pretransposed formula from their cheatsheet which was generally effective if copied correctly"  or something along those lines

[zsteve]

I'm aware of the convention of describing flux like a vector, e.g. 'flux change upwards' or 'flux change downwards' but flux is a scalar.
Could someone just confirm that this convention is simply due to assigning directions to the sign of flux change? (otherwise it would be dodgy )

[odeaa]

I'm aware of the convention of describing flux like a vector, e.g. 'flux change upwards' or 'flux change downwards' but flux is a scalar.
Could someone just confirm that this convention is simply due to assigning directions to the sign of flux change? (otherwise it would be dodgy )

I usually say increasing/decreasing flux and it's polarity rather than give a direction which I think is more accurate. At the very least, I haven't been penalised for it so I don't think it's inaccurate (for vce anyway).

Lzxnl or someone else may be able to clarify but I don't think you would lose marks in vce for describing it like that

[lzxnl]

Strictly speaking, your magnetic flux is due to a vector integral over a surface. This integral has, in its definition, the direction of your surface in-built. So, although the magnetic flux is technically a scalar, its calculation does require the orientation of your surface.

In common-sense terms, imagine you have a door and you're shooting water with a toy gun through it. You can consider the water flow as positive going into the door, or negative going out of the door on the other side. The sign in the magnetic flux is analogous to the sign of your 'water flux'.

You can't really learn electromagnetism properly in high school. Or even in first year uni. You just don't have the mathematical tools to do so.

[GeniDoi]

Nah in the assessors report they often say "some students used a pretransposed formula from their cheatsheet which was generally effective if copied correctly"  or something along those lines

It's not a cheat sheet if it's endorsed by the examiners...

[schooliskool]

Just a quick one, if you get an answer of 41666.7 etc, should I round it to 4.2 x 10^4?
I don't do it but does it matter?

[Mc47]

Could anyone help me out with this question?



Cheers

[Orson]

Could anyone help me out with this question?

Sure! Could you please tell me what paper it was? I've seen it (and done it). I just want to double check!

The answer is: C A D C

C: The signal wave. This is the initial medium, in this case it is sound.

A: The carrier wave. (I'm not sure how to explain this...can someone jump in?)

D: The modulated signal. This is the signal piggybacking, or being superimposed on the medium of transmission. (This could be through a Laser Diode sending, and a Photodiode receiving).

C: The signal wave. This is the output, again sound, only it has been amplified.

I'm sure someone can explain it in more detail. Remember to put this on your summary sheet, along with a definition for modulation.

[odeaa]

Anyone here done the exampro challenge exam? Mind sharing what you got?

[Mc47]

Sure! Could you please tell me what paper it was? I've seen it (and done it). I just want to double check!

The answer is: C A D C

C: The signal wave. This is the initial medium, in this case it is sound.

A: The carrier wave. (I'm not sure how to explain this...can someone jump in?)

D: The modulated signal. This is the signal piggybacking, or being superimposed on the medium of transmission. (This could be through a Laser Diode sending, and a Photodiode receiving).

C: The signal wave. This is the output, again sound, only it has been amplified.

I'm sure someone can explain it in more detail. Remember to put this on your summary sheet, along with a definition for modulation.

Ahh okay cheers. It was NEAP 2014

When you say put it on your summary sheet, are the answers always going to be the same?

[Orson]

Ahh okay cheers. It was NEAP 2014

When you say put it on your summary sheet, are the answers always going to be the same?

In my experience, these have a pattern. I'll find another example and post it. Stay posted mate. When I say put it on your summary sheet, I mean put the question on it. Then if you get a similar question, you can use it to work backwards or something. The answers won't be the same...I can't guarantee that.

[Orson]

Anyone here done the exampro challenge exam? Mind sharing what you got?

Haha...thanks for reminding me to do that. I'll let you know when I do it...

[zsteve]

Just a quick one, if you get an answer of 41666.7 etc, should I round it to 4.2 x 10^4?
I don't do it but does it matter?

Yeah I would, definitely wouldn't leave the raw value. The num of sit figs you leave depends somewhat on your input, but not strictly as in chem

[Adequace]

Can someone confirm if these energy/work formulas are legitimate, they were in our notes from my teacher but people have told me they're wrong.

Ek: work done by force - W=1/2mv^2 * x
Ug: work done by gravity - W=mgh * x
Thermal Energy: work done by friction - W=Fr * x

Cheers

[GeniDoi]

Can someone confirm if these energy/work formulas are legitimate, they were in our notes from my teacher but people have told me they're wrong.

Ek: work done by force - W=1/2mv^2 * x
Ug: work done by gravity - W=mgh * x
Thermal Energy: work done by friction - W=Fr * x

Cheers

Well work = force * distance, but the first two of those formulae aren't in terms of a force, so they are wrong.

The first equation, whoever made it was probably going for W = ΔKE which leads to v^2 = u^2 + 2ax.

The second equation, close but not quite... Work = Force * distance = GMm/r^2 * distance for gravity. Since for most situations the Δr is very small it's possible to approximate GMm/r^2 to mg, so Work = mg * x = mgx = mgh.

The third one is correct but usually friction is W(friction) < 0 and friction opposes the motion and hence removes energy from a system.