HSC Physics Question Thread

[jamonwindeyer]

Is that all we have to know? thanks pikchu. still interested in how it works beyond the course tho, maybe a certain quantum physicist could send some info our way?

Yep, so provided you (roughly) understand the idea of how Cooper Pairs form and such, you don't need to go into the Meisner Effect a whole lot. Important to know that superconductors also have the property of exactly cancelling out any changing magnetic fields with eddy currents - But as above, this is separate to the Meisner Effect.

The Meisner Effect is a very complex quantum mechanical effect. I've sort of had it explained to me I think (I could never possibly do it justice lol), but I'm pretty sure it is beyond what can be handled without properly studying quantum mechanics. Indeed, it's also something we are still investigating - This isn't like semiconductors, that we understand quite well. Superconductors are a huge topic of research right now - We're always learning more

[winstondarmawan]

Would appreciate help with the following:
21. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21557082_1321052058020314_955487187_o.jpg?oh=14d3385cf665d072aba1485eac630b1e&oe=59B61DD6
TIA

Believe my post got missed.
What is the best approach for the above question?
Also for this question:
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21534597_1846449502338173_1092053360_o.jpg?oh=36b00078af6bf1bf34c14bbef3561e49&oe=59B790FD
How is the answer B? An explanation would be greatly appreciated.
Thanks in advance.

[jamonwindeyer]

Believe my post got missed.
What is the best approach for the above question?
Also for this question:
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21534597_1846449502338173_1092053360_o.jpg?oh=36b00078af6bf1bf34c14bbef3561e49&oe=59B790FD
How is the answer B? An explanation would be greatly appreciated.
Thanks in advance.

Hey! For the earlier post, you'd be focusing on Edison/Westinghouse and the role financial motivations played in the competition for which distribution system to use. In honesty, I'd probably be picking space exploration there - A lot of the space scientists you cover in that topic developed their technology due to funding from the World Wars. That's an easier link in my opinion

For the latter, the time we are given is \(t_v\) to use in the formula. We know this because time passes by more slowly for a body in motion - That 10 year timeframe is the value that has been 'stretched' relative to earth. So to find the original:

[kiwiberry]

21. https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/21557082_1321052058020314_955487187_o.jpg?oh=14d3385cf665d072aba1485eac630b1e&oe=59B61DD6
TIA

Sorry for missing this!! For the electricity distribution systems, I would agree and talk about the rivalry between Westinghouse (AC) and Edison (DC). At first, Edison's DC electricity was favoured because technology using it was well established. However, because DC could only be distributed at the voltage it was to be used, there were large, expensive power losses and it could only be distributed over short distances. AC electricity, introduced by Westinghouse, was able to overcome these shortcomings through the use of transformers. Recognising the threat this posed to his business, Edison tried to ban the use of AC and prove that it was dangerous by electrocuting animals and using it in the first electric chair, despite knowing the benefits of AC to society.

[winstondarmawan]

We know this because time passes by more slowly for a body in motion - That 10 year timeframe is the value that has been 'stretched' relative to earth. So to find the original:

If time passes more slowly in a body of motion, wouldn't the time elapsed on Earth be a greater value?

[jamonwindeyer]

If time passes more slowly in a body of motion, wouldn't the time elapsed on Earth be a greater value?

Time passing more slowly results in a smaller value - That is, if you watch a clock on a body moving very quickly for 1 year, less than 1 year will pass on the clock. A smaller value.

Hmm, on Googling this question apparently it's a bit controversial, I understand why.

The issue is that we are taking both measurements, the 10 years and the one we calculate, from the relativistic frame of reference. I see where your answer comes from, but consider it this way. The way the question is worded, the spaceship is the observer. The earth is the thing moving away at 0.8c (remember, relativity, both are valid). So, the time on earth should be slower compared to the spaceship, purely because we've chosen the spaceship as our frame of reference.

Now we are measuring a time of 10 years as the earth moves away - That is \(t_v\), because we are the observer watching the earth move away at speed, our value is affected by special relativity. \(t_0\) is the unknown, the value unaffected by special relativity

I wouldn't stress about this question - It's poorly framed at best

[winstondarmawan]

Would appreciate help for the following:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21584700_1322520041206849_361794579_n.png?oh=2863b97b71c254113417eadfe759b600&oe=59B8BA81
Here are the values if it is not readable from the above pic:
Mass of block: 30g
Hangs 4.25cm from the axle.
Dimensions of armature: 4cm x 8.5cm
Current: 2.47x10^-3 A
Magnetic Field Strength: 0.12T
Thanks in advance!

[kiwiberry]

Would appreciate help for the following:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/21584700_1322520041206849_361794579_n.png?oh=2863b97b71c254113417eadfe759b600&oe=59B8BA81
Here are the values if it is not readable from the above pic:
Mass of block: 30g
Hangs 4.25cm from the axle.
Dimensions of armature: 4cm x 8.5cm
Current: 2.47x10^-3 A
Magnetic Field Strength: 0.12T
Thanks in advance!

Hey!
Because the motor does not rotate, the torque due to the weight force of the block must equal the torque due to the motor effect:
\(\theta\) will be 0 because the armature is horizontal, and we can sub in the rest of the values to find n

[gilliesb18]

Hello
I have an exam tomorrow for physics and I just have a few questions from a past paper that I would appreciate some help on....
1. Explain how Einstein's famous equation E=mc^2 relates to the Big Bang theory.
2. If crumple zones help reduce injuries to people during collisions, why then is the cabin of the vehicle made so rigid??

Thanks!!!!

[blasonduo]

Hello
I have an exam tomorrow for physics and I just have a few questions from a past paper that I would appreciate some help on....
1. Explain how Einstein's famous equation E=mc^2 relates to the Big Bang theory.
2. If crumple zones help reduce injuries to people during collisions, why then is the cabin of the vehicle made so rigid??

Thanks!!!!

Hello! I am a bit rusty on these questions, (especially 1) so apologies if you wanted more

1) The big bang theory suggested that energy expanded at an extremely fast rate before slowing down to a slower pace while producing matter. E=mc^2 is a way to vaguely explain this. From this, we see that the big bang produced matter instead of producing energy.

2) We need crumple zones to significantly decrease the energy input into the car. The more it "crumples", the more energy dissipates before entering the human. HOWEVER, if this cabin was not sturdy, it would also crumple, but into the passengers! This crumpling could be more dangerous than the initial impact as the crumpled zone is now being "intruded" into you!

I know these explanations aren't the best, but I hope they help

[winstondarmawan]

Quanta to Quarks:
What is the weak nuclear force and it's role in holding nucleons together?
TIA.

[austv99]

Would appreciate help in understanding these three questions
All from 2005 HSC
Can someone clarify what Enrico Fermi did for beta decay? (Quanta to Quark)

Mod Edit: Post merge

[jakesilove]

Quanta to Quarks:
What is the weak nuclear force and it's role in holding nucleons together?
TIA.

Hey! The weak nuclear force is one of four fundamental forces in our universe. Relative to the strong nuclear force, it has a strength of 10^(-6). The weak nuclear force operates across distances 0.1% of the diameter of the Proton, and so operates at REALLY, REALLY small scales, such as the interaction of nucleons! They are also important in the interaction of quarks and leptons. Not too sure if you would need to know more detail than this; I definitely don't!

[kiwiberry]

Quanta to Quarks:
What is the weak nuclear force and it's role in holding nucleons together?
TIA.

Another thing to remember is the fact that the weak nuclear force is carried by the intermediate vector bosons W/Z. But yeah, I'm pretty sure we don't need to know this in much detail, what Jake said is probably more than enough!

Would appreciate help in understanding these three questions
All from 2005 HSC
Can someone clarify what Enrico Fermi did for beta decay? (Quanta to Quark)

Mod Edit: Post merge

Hey!

6) The induced current is proportional to the rate of change of flux. The speed that the wire rotates will definitely change this, so C is wrong. When the wire is north-south, it will be parallel to the Earth's magnetic field, and it will cut much less flux than if it was east-west, so D is also wrong. I'm not sure why B is the answer though - can someone else lend a hand?

15) First of all, the electrons and holes won't speed up or slow down, because the force due to the mag field will be at right angles to the mag field and the particle's velocity, so we can eliminate A and B. Due to the current, the electrons will move to the closer end and the holes to the further end. Using the right hand grip rule, both electrons and holes will move to he bottom of the rod (remember to flip the direction of the force for negative particles, so the answer is C

5) Maximum range will be when the angle of elevation is 45^o, so since 40^o and 50^o are both 5^o out from this, both will have the same range. When the angle is 50^o, the vertical component of the particle's velocity will be larger, so it will have a longer time of flight, hence C

Fermi was the one who formally proposed the theory that a neutron is transformed into an electron, proton and antineutrino during beta decay.

Hope this helps

[austv99]

15) First of all, the electrons and holes won't speed up or slow down, because the force due to the mag field will be at right angles to the mag field and the particle's velocity, so we can eliminate A and B. Due to the current, the electrons will move to the closer end and the holes to the further end. Using the right hand grip rule, both electrons and holes will move to he bottom of the rod (remember to flip the direction of the force for negative particles, so the answer is C



Fermi was the one who formally proposed the theory that a neutron is transformed into an electron, proton and antineutrino during beta decay.

Just to clarify, for 15, the holes move in same way as electrons because they are relatively positive but not considered positively charged? And they wont speed up or slow down since to do so, the force must be in the same direction of motion? In this case it's down?
If a question was about how fermi contrubuted to understanding of beta decay, would pauli be explained first?