HSC Physics Question Thread

[jamonwindeyer]

How would you do the question in the attachment below?
Thanks in advance.

This one is nasty - I remember this, it is a copy of a question from a 2004 paper, with some dates changed!

So the idea is this. Consider Kepler's Law:



Mars has a larger orbital radius than the Earth, so according to this equation, it must also have a larger orbital period. We can't calculate exactly how much, especially given that the diagram is not to scale (or at least specified to be), but we know that it is larger. What does this mean? Well, in the 10 months time span you have been given, earth will complete about 5/6 of a revolution. Mars will complete less than this - I'd say about 1/2 of a revolution might be what you want.

We also know that they are going anticlockwise. Why? Well, that's just what we need for this scenario to make sense. Putting all that together, I'd get this:



Not 100% confident on this, but this would be my best crack (also excuse the shitty diagram lol)

[jamonwindeyer]

Thanks, also is this prac done individually or in groups. I'm so nervous as it is worth 20%. 

Probably individually, but it depends on your school! don't be nervous! It is only Year 11 after all, the results this year don't count in the long run - Just  use this as a gauge to see how you'd go in a prac in Year 12

[bluecookie]

When you increase the Voltage of the primary Current of the Primary decreases. Vp/Vs = Is/Ip. Yeah if you multiply both numerators by K you will increase the value of the Voltage of the Primary and Current Current Of The Secondary. Therefore current of the primary(the denominator Ip) decreases because the numerator Is gets bigger than Ip. So you increased the voltage for the Primary coil and the Current in that coil (Ip) decreased while the current in the other coil Increased (Is)

Oh, so it's inversely proportional with the primary voltage/current, not the primary voltage/secondary current. Ah, I see Thanks for clearing up that misunderstanding for me! (:

[bluecookie]

np>ns for step down because emf is proportional to the number of coils, so a smaller number will induce a smaller emf in the secondary coil and vice versa for step up

Thanks

[winstondarmawan]

This one is nasty - I remember this, it is a copy of a question from a 2004 paper, with some dates changed!

So the idea is this. Consider Kepler's Law:



Mars has a larger orbital radius than the Earth, so according to this equation, it must also have a larger orbital period. We can't calculate exactly how much, especially given that the diagram is not to scale (or at least specified to be), but we know that it is larger. What does this mean? Well, in the 10 months time span you have been given, earth will complete about 5/6 of a revolution. Mars will complete less than this - I'd say about 1/2 of a revolution might be what you want.

We also know that they are going anticlockwise. Why? Well, that's just what we need for this scenario to make sense. Putting all that together, I'd get this:

(Image removed from quote.)

Not 100% confident on this, but this would be my best crack (also excuse the shitty diagram lol)

So say if I assumed the diagram was to scale like and calculated the approximate location of Mars that way (it turned out to be 1/7th of the rotation) would that be okay if I didn't state any calculations?

[jamonwindeyer]

So say if I assumed the diagram was to scale like and calculated the approximate location of Mars that way (it turned out to be 1/7th of the rotation) would that be okay if I didn't state any calculations?

Hmm, I would say that assuming the diagram is to scale is probably not a correct thing to do. But then, given how little info you are given, it is a logical assumption to make. You'd probably get paid anyway as long as the rest of your reasoning was okay -  Definitely don't assume diagrams are to scale in HSC/Trial exams though

[Aaron12038488]

I completely flunked physics, the prac which is light going through a glass perspex. My CRO didnt work which wasted like 5-10 min. I didnt know how to answer the questions and its worth 20%. I'm so bad at practicals, however when it comes to tests, I always ace it.
Need urgent advice to improve on pracs and hopefully doesnt occur in year 12.

[winstondarmawan]

Would appreciate help with the question in the attachments.
Thanks in advance.

[ProfLayton2000]

Hello, why doesn't an AC induction motor have any back emf?

[jamonwindeyer]

I completely flunked physics, the prac which is light going through a glass perspex. My CRO didnt work which wasted like 5-10 min. I didnt know how to answer the questions and its worth 20%. I'm so bad at practicals, however when it comes to tests, I always ace it.
Need urgent advice to improve on pracs and hopefully doesnt occur in year 12.

Damn! That's bad luck Aaron, fingers crossed your mark comes out a little better than you anticipate! Once you get your feedback, just try and recognise, "Where did my marks go?" Did you understand the theory? Was your process correct? Do you need to work on time management?

Learn from mistakes my friend - That is what Year 11 is for!

[jamonwindeyer]

Would appreciate help with the question in the attachments.
Thanks in advance.

Hey Winston! Actually doing this experiment, the graph would be two peaks, one negative one positive. Whichever peak you put second would be larger.

To explain the shape: As the magnet falls it exposes the tube to a changing magnetic field, inducing a current. This reaches a peak before minimising as the magnet reaches the centre of the tube. Then, as it falls out, the changing field is now in the opposite  direction, so you get a peak in the other direction. It is moving faster than it did in the first half, so the peak is larger.

Hope that helps!!

[jamonwindeyer]

Hello, why doesn't an AC induction motor have any back emf?

Hey ProfLayton! AC induction motors don't have back emf because we don't feed them a current - We actually RELY on induced currents to make it spin!! Back EMF is normally considered as an induced current flow due to our supply current - No supply means no back emf

[Aaron12038488]

Out of curiosity, what is an open-investigation. I saw my assessment booklet, and it stated that.

[jamonwindeyer]

Out of curiosity, what is an open-investigation. I saw my assessment booklet, and it stated that.

Pretty much just an investigation/research task without a definite answer - Pretty much any take home task you receive for Physics will fall under this category

[katnisschung]

a little clueless as to how they got v..

i got r to be 1.00x10^17 and then i can't exactly sub
this into the escape velocity formula cos it isn't the radius ..