VCE Physics Question Thread!

[Stevensmay]

In order to replace the fuse as safely as possible, which of the following is the best precaution for Joan to
take?
A. stand on a rubber mat
B. switch off the mains supply
C. disconnect the transformer from the mains supply
D. remove the load from the transformer

Why C instead or B?

This is just my thought process.
Switch could fail and not actually disconnect power to the fuse.
Unplugging it guarantees there will be no power to the fuse, therefore no chance of electrocution.

I think this would be a case of, one answer is slightly better than the other.

[Robert123]

Photonics (detailed study) question,
Could someone please explain the what "numerical aperture" and "acceptance angle". I can usually get MC questions related to them right by applying the formula but I have no genuine idea what the numbers even mean.
Cheers

Bumping this

Energy level diagram question:
E(eV)
0         N= infinite
-1.38   N=5
X         N=4
-1.94   N=3
Y         N=2
-5.13   N=1
A photon of 3.61eV is absorb by the ion. Moments later, photons with energy 0.42eV and 1.5eV are ejected from the atom. Use the information provide to calculate the energy levels at n=2 and n=4.

For n=1 to n=4,
5.13-3.61= 1.52eV
This agree with the energy level for n=3 since
N=4 to n=3
1.94-1.52= 0.42eV
The issue I'm having is getting the right n=2 since the 1.5eV could come from n=3 (giving a value of -3.44eV) or from n=4 (giving a value of -3.02eV).  The answer gives -3.02eV but how is this more right than -3.44eV since both could be ejected.
So which one is 'more right'? If vcaa ask a question like this would they give both answers as correct or just one?

[SocialRhubarb]

The key here is that you're dealing with a single atom absorbing a single photon.

If the jump from N=4 to N=2 gives us a 1.5 eV photon, it can no longer produce a photon with an energy of 0.42 eV, hence it cannot jump from N=4 to N=2 to produce a 1.5 eV photon.

[Jaswinder]

what effect does changing the slit width have on the diffraction pattern?

[Stevensmay]

Our equation for the extent of diffraction is where w is the width of the slit.
We can see that as we increase w, becomes smaller, thus less diffraction occurs.
As we decrease w, more diffraction occurs as is now bigger.

This also explains why we need to use very thin slits/apertures for this experiment, as if they are too big any diffraction is not evident.

[lolipopper]

Our equation for the extent of diffraction is where w is the width of the slit.
We can see that as we increase w, becomes smaller, thus less diffraction occurs.
As we decrease w, more diffraction occurs as is now bigger.

This also explains why we need to use very thin slits/apertures for this experiment, as if they are too big any diffraction is not evident.

what about the intensity of the pattern? and what effect does it have on the fringe spacing?

[BasicAcid]

what about the intensity of the pattern? and what effect does it have on the fringe spacing?

No effect on the intensity and as the diffraction is larger, the diffraction patterns are also larger, i.e. the fringe spacing is larger

[barydos]

Hello
This question came from exam 1 of the VCAA 2006 paper:

Spoiler

The assessment report's comment:

Spoiler

I'd just like to know what your responses might be, because I feel the provided comment is insufficient.

[Alwin]

offtopic

Dont be smartass alright. It was a genuine question.

i just got the physics marking scheme from my teacher. it says "where questions dont specify that the working must be shown, if the correct answer is in the box the student receives full marks". Maybe you should get some suffice information yourself before absolutely classifying other peoples question invalid and, from the sound of your tone, stupid.

Sorry lolipopper if I made you feel like you'd asked a "stupid question" or anything, I didn't mean it in that way. I was just joking with you, about the "read the instructions first" part I put in the picture. I haven't been on this thread in a while, been rather stressed for Indo oral exam so again I apologise for being or seeming a bit short with you.
I was just showing the source of my "information". I can only talk about the pre-2012 exam marking scheme, and as Tim...blahhh has confirmed from more accurate sources Re: Physics [3/4] Question Thread! it turns out I was wrong. Not going to blame the practise exam, it's just that it turns out I was wrong and I'm sorry if my response was inconsiderate.

Good luck to everyone with physics

[sin0001]

With questions talking about the extent of diffraction: do we assume that max. diffraction occurs when wavelength/width ratio ~ 1 or when this ratio is a large value?

[lolipopper]

offtopic

Sorry lolipopper if I made you feel like you'd asked a "stupid question" or anything, I didn't mean it in that way. I was just joking with you, about the "read the instructions first" part I put in the picture. I haven't been on this thread in a while, been rather stressed for Indo oral exam so again I apologise for being or seeming a bit short with you.
I was just showing the source of my "information". I can only talk about the pre-2012 exam marking scheme, and as Tim...blahhh has confirmed from more accurate sources Re: Physics [3/4] Question Thread! it turns out I was wrong. Not going to blame the practise exam, it's just that it turns out I was wrong and I'm sorry if my response was inconsiderate.

Good luck to everyone with physics

im sorry too bro. all good. and good luck to you too.

With questions talking about the extent of diffraction: do we assume that max. diffraction occurs when wavelength/width ratio ~ 1 or when this ratio is a large value?

yes, the size of the aperture must be approximately the same as that of the wavelength for significant diffraction to occur.

Mod Edit - Merged double posts (Phy124)

[joey7]

Quick question
"The shape of racing cars is designed to minimise air resistance. To a reasonable approximation the force (F) or air resistance is proportional to the square of the speed (v). That is: F=kv^2 where k is the drag coefficient.:

Which if the following choice is a possible unit for K
A. kgm^-1
B. s^2m^2
C. N
D. Nm^2s^-1
E. S^2M^-2

[SocialRhubarb]

Force is equal to mass times acceleration, so it has the units of mass, kg, times acceleration, ms^-2, so force has the units of kg m s^-2.

v² has the units of m² s^-2.

k=F/v²=kg m s^-2 m^-2 s²=kg m^-1

So the answer is A, kg m^-1.

[lolipopper]

what is a good answer to the following:
-what is modulation and demodulation?

[Jaswinder]

I understand Question 9 and question 14 in motion 
http://www.vcaa.vic.edu.au/Documents/exams/physics/physics1w06.pdf

thanks