HSC Physics Question Thread

[Cindy2k16]

I definitely didn't think I aced the exam. It was a seriously weird paper (2014 was a weird mix of easy and just bloody strange), and so I wasn't hugely confident with my performance. Like, I was sure I did fine, but I definitely didn't think I aced it or anything like that! We're all bad judges of ourselves, so once you walk out of the exam room, you may as well just forget the paper and move on. There's no way to tell what is a good raw mark, and what is a bad raw mark, because you have no idea how the rest of the cohort went. You seem completely ready to smash the exam, and that's all that's important. You'll do great tomorrow

Haha I see. That's kind of reassuring because I practically never feel great about my performance after exams. And me? ready? thats the opposite of how I ever feel for exams lol especially this one. I am probably one of the most stressed people at my school. I hope I'll do okay. My school has a pretty inconsistent performance in science subjects in the hsc so that's kind of nerve wracking... I just badly want this all to finish!

[JemexR]

Hi for 2010 q32
"Two significant problems that will affect a manned spaceflight to Mars are:
-the changes in gravitational energy
- protecting the space vehicle from high-speed electrically charged particles from the Sun
Use your understanding of physics to analyse these problems"
8 marks

How could you answer this question? is it necessary that we know about the gravitational field/atmosphere etc of Mars?
TIA

Haha, I had the answer for this question for some reason;

Change in GE - humans are essentially designed for gravity on Earth, and given that gravity on Mars is less than that on Earth, and due to the zero gravity experienced during space travel, being in this environment can cause some serious health issues such as muscle weakening and loss of bone density.

High-speed particles - These charged particles are particularly dangerous to humans due to their ability to cause mutations in DNA, hence causing multiple problems such as cancer

[Taylah Jensen]

Hiiiii,

Would someone please be able to tell me the thought process behind this question? I feel like the answer has something to do with the right hand push rule, and there's some key in the fact the magnetic field is "then applied" meaning a change in magnetic flux, but I can't justify the answer ahaha.

Thank you!!

[Cindy2k16]

Hiiiii,

Would someone please be able to tell me the thought process behind this question? I feel like the answer has something to do with the right hand push rule, and there's some key in the fact the magnetic field is "then applied" meaning a change in magnetic flux, but I can't justify the answer ahaha.

Thank you!!

Hi I answered this before so I'll just copy past my answer:
The electrons and holes move in opposite directions in an electric field. If you use your right hand palm rule for the conventional current (movement of positive charge) youll find there is a downwards force on the 'holes'. Now electron flow is in the OPPOSITE direction to conventional current. So when you use your left hand palm rule (or whatever youve been taught to use for the flow of a negative charge) you point ur thumb in the OPPOSITE direction to the conventional current and youll find that the electrons ALSO experience a downwards force.
Thus both holes and electrons move to the bottom of the rod ie. the same side of the rod.
Therefore C.
For this question, induction isn't used to answer it. Its more about the force experienced by charged particles in a magnetic field 
hope this helps

[Taylah Jensen]

Hi I answered this before so I'll just copy past my answer:
The electrons and holes move in opposite directions in an electric field. If you use your right hand palm rule for the conventional current (movement of positive charge) youll find there is a downwards force on the 'holes'. Now electron flow is in the OPPOSITE direction to conventional current. So when you use your left hand palm rule (or whatever youve been taught to use for the flow of a negative charge) you point ur thumb in the OPPOSITE direction to the conventional current and youll find that the electrons ALSO experience a downwards force.
Thus both holes and electrons move to the bottom of the rod ie. the same side of the rod.
Therefore C.
For this question, induction isn't used to answer it. Its more about the force experienced by charged particles in a magnetic field 
hope this helps

Yes! Thank you so much

[Mei2016]

Hi, for those who have done quanta to quarks and can help out...

for 2011 Q34 c) for forces in the atomic nucleus, is electrostatic only for protons to protons or electrons to electrons? (so it's direction is always 'repulsive'?) or could it be between protons and electrons (then the direction would be 'attractive')
-and isn't the direction for SNF attractive at certain distances and then repulsive if the distances are less than 1x10^-15m? ( the answers for the table in Q34c) only had 'attractive' as the direction...)

[imtrying]

Just to clarify: when determining the force on a negative charge do I just point my thumb in the direction of negative current using RHP rule  or do I have to use my left hand?

[RuiAce]

Just to clarify: when determining the force on a negative charge do I just point my thumb in the direction of negative current using RHP rule  or do I have to use my left hand?

Either works.

[imtrying]

Either works.

Thanks for the quick reply! Having a bit of a last minute panic there haha

[nimasha.w]

hi! 2 things - whats a simple prac to remember for the production and receiving of radio waves and one for the production of alternation current (i don't understand the ones we did in class)

[MysteryMarker]

Hi, for those who have done quanta to quarks and can help out...

for 2011 Q34 c) for forces in the atomic nucleus, is electrostatic only for protons to protons or electrons to electrons? (so it's direction is always 'repulsive'?) or could it be between protons and electrons (then the direction would be 'attractive')
-and isn't the direction for SNF attractive at certain distances and then repulsive if the distances are less than 1x10^-15m? ( the answers for the table in Q34c) only had 'attractive' as the direction...)

Yo, for your first question about the forces in the atomic nucleus, within the nucleus there only exists two particles. These include protons and neutrons. Hence as electrostatic force is only experienced by charged particles the only charged particle within the nucleus is the proton, resulting in the electostatic force between protons to be repulsive as like opposes like. Sure the electrostatic force between a proton and electron is attractive, but within the nucleus these electrostatic forces act to repel each other. 

For your second question, yes SNF is repulsive at very short distances and attractive for distances after that. The answers given in Q34c) I believe are very ambiguous because you are just stating their relative strengths. Hence I assume they just wrote attractive as in the second column we wrote that electrostatic forces are repulsive and to counteract this we have an attractive force from the SNF.

This is just my take on these questions, take these answers with a grain of salt! I'm also a year 12 student about to lose his virginity tomorrow (I don't count english cause that was bloody rape), so yeah hope this helps!

[imtrying]

For Einstein's contribution to quantum theory, am I missing anything?
- extended quantum theory to all forms of EMR not just black body radiation
- proposed light interacted with matter as photons (and hence proposed the photoelectric effect)
(This is for the ideas to implementation topic )

[proficles]

Hi, for the mass defect, do you include the mass of electrons?

[MysteryMarker]

hi! 2 things - whats a simple prac to remember for the production and receiving of radio waves and one for the production of alternation current (i don't understand the ones we did in class)

Yo, for your first one I've just attached a screenshot of the 2008 HSC solution for a similar question.

http://prnt.sc/d0rzj3

For your second one to demonstrate the production of AC, this is going to be very simplified and basic, but I reckon something along the lines of moving a magnet in and out of a solenoid connected to a galvanometer should do. Unless the moderators, the actual smart people, have a genius way of producing an alternating current .

[Cindy2k16]

Hi for back emf, so when a motor is running at a constant speed with no load attached, the back emf will equal the supply emf and so the net emf is zero. Thus current in the coil should be zero right? ( http://www.physics.usyd.edu.au/teach_res/hsp/u6/t6_lenz.pdf )
But if this is the case, how come current is measured when an ammeter is attached to the motor? Is this because the galvanometer is considered a load?

TIA