VCE Physics Question Thread!

[HopefulLawStudent]

Soooo... y'all confused me. (sorry... be rest assured tho, it's definitely me, not you. My brain just can't comprehend physics in general.)

So I went digging around on VCAA (this is a past exam question; probably shoulda checked there first but didn't even think to; it turns out the answer given in the teacher-compiled handout I got was completely and utterly wrong). It turned out to be a 2015 question and omg. This question was done incredibly poorly (11% got full marks for part a and 79% got 0 marks).

For anyone who's interested answer is attached.

And while I was typing this message (was originally gonna ask y'all to explain it cuz VCAA didn't offer an explanation in the exam report beyond "y'all screwed up. do better" and then something clicked and I got it so everything's a-okay again. Thanks guys!

[Swagadaktal]

Yeah it's just decided by the person.

I accidently misread your comment. It isn't a U shape, it's literally a trapezium. It'll first be increasing at a constant rate, then it'll be constant (entire loop is in the magnetic field), then it'll decrease at a constant rate with the same magnitude as it did when it was increasing.

It shouldn't matter if the shape is positive or negative, it just shouldn't be in both from my understanding.

Yeah I meant trapezium. Lmao my explanations. Yeah defs not a U shape soz if I misled you there.

Edit: I refuse to acknowledge the existence of trapeziums after methods exam 1 q10d.
But yeah trapezium - soz about that it would've been really confusing thinking it was a U shape. In my mind I think of it as a linear U shape (not as a trapezium for some reason lmao)

[Swagadaktal]

Soooo... y'all confused me. (sorry... be rest assured tho, it's definitely me, not you. My brain just can't comprehend physics in general.)

So I went digging around on VCAA (this is a past exam question; probably shoulda checked there first but didn't even think to; it turns out the answer given in the teacher-compiled handout I got was completely and utterly wrong). It turned out to be a 2015 question and omg. This question was done incredibly poorly (11% got full marks for part a and 79% got 0 marks).

For anyone who's interested answer is attached.

And while I was typing this message (was originally gonna ask y'all to explain it cuz VCAA didn't offer an explanation in the exam report beyond "y'all screwed up. do better" and then something clicked and I got it so everything's a-okay again. Thanks guys!

Pwoah 11% only? Like by the end of the year you'd expect more wouldn't you?
Is this as hard as the questions get in physics?

Glad to see everything is A-OK . Cant believe that VCAA physics explanations are aligned with the explanations in the crappy textbooks. Give us a break physics .

EDIT: Damn teacher giving you different answers? That would give me trust issues tbh..

Btw gonna do this to save some time for the mod
Mod note: Merged double post. You can edit previous posts.

yw fam

[HopefulLawStudent]

Btw gonna do this to save some time for the mod
Mod note: Merged double post. You can edit previous posts.

#SwagForMod2k17

[HopefulLawStudent]

Question: What's the formula for maximum EMF? (Is it that 2pi*fNBA*sin(2pi*ft) thing or is it 2pi*fNBA?) + Is that in the study design?

[zsteve]

Question: What's the formula for maximum EMF? (Is it that 2pi*fNBA*sin(2pi*ft) thing or is it 2pi*fNBA?) + Is that in the study design?

EMF is given by Faraday's Law of Electromagnetic Induction:

As where is the angular velocity (basically how many radians/sec your coil spins at)

Hence .

The other formula with sine is the emf at any time during the coil's rotation. Letting sin(...)=1 gives the max emf.

[HopefulLawStudent]

EMF is given by Faraday's Law of Electromagnetic Induction:

As where is the angular velocity (basically how many radians/sec your coil spins at)

Hence .

The other formula with sine is the emf at any time during the coil's rotation. Letting sin(...)=1 gives the max emf.

Gotcha. Thank you! Just wondering: Is the max emf thing in the study design? My teacher seems a bit vague about whether or not it is... :/

[Adequace]

Just wondering have you guys been taught your detailed study before starting unit 4?

[Swagadaktal]

Just wondering have you guys been taught your detailed study before starting unit 4?

Yeah

[HopefulLawStudent]

Just wondering have you guys been taught your detailed study before starting unit 4?

Nope.

[sweetiepi]

Just wondering have you guys been taught your detailed study before starting unit 4?

Yeah. My class actually did it before moving onto electricity.

[lzxnl]

Gotcha. Thank you! Just wondering: Is the max emf thing in the study design? My teacher seems a bit vague about whether or not it is... :/

You'd be pretty stiff to get a question on that. I never saw it on SACs or on the exam.
Then again, I never understood why VCAA decided to make it possible to take physics without methods because it really makes no sense teaching it without maths. It's a bit like teaching someone addition without teaching them to count. Sure, you can remember 5+5=10, but good luck knowing what 5 means.

Just wondering have you guys been taught your detailed study before starting unit 4?

Depends on detailed study. Further electrons/structures and materials are related to unit 3 content, so they might be taught before unit 4. Sound is related to unit 4 so it'd be taught during/at the end of unit 4.

[solution]

Can someone check the first two pictures please. For the last one, how do I solve the simulataneous equations using a scientific calculator only? (I had to use a CAS for it)

[NerdyPi]

Hi guy, I really need some help with this question (in preparation for the electric power explanation type SAC),

Explain why an alternator results in an AC output voltage? ...

My response was :
Faraday’s law states that the induced emf is equal to the rate of change of flux. As a coil initially rotates, it is on one particular side (take as positive), so as the maximum initial flux decreases to zero, (negative rate of change), a positive (according to Lenz’s law) voltage in induced.
After this, the coil is on the opposite side, and rotates from 0 flux to a maximum flux (in opposite direction, so is negative); this is a hence still decreasing flux, so a positive emf is induced.
Then, as the coil rotates from –max flux to 0, the rate of change of flux is increasing, hence inducing a negative voltage.
Therefore, as coil rotates from a positive to negative flux (and continues this cycle), flux both increases and decreases, so both a positive and negative flux is induced.

But I have been told this is wrong as flux is a scalar, and that it has something to do with the current? Can someone please clarify this for me? Thanks heaps

[lzxnl]

Flux IS a scalar, but it's a scalar that takes positive and negative values. If defined properly, it has to be defined with a consistent choice of surface direction. What I mean is, you need to measure flux in a way such that if the surface flips 180 degrees, the flux changes sign, obviously. So in this way, you do have to specify a direction for the flux, but this direction is only a convention for how your flux was defined.

Mathematically, flux is a scalar because it arises from a dot product of two vectors: the magnetic field vector and the surface normal.