HSC Physics Question Thread

[jamonwindeyer]

To anyone who wanted it, a quick video explanation of those power formulae discrepancies can be found here

[Bubbly_bluey]

Hi we just did "Lenz's Law on Moving Conductors (Sheets) and i am really confused as to how a metal plate with slits has a slower stopping motion than a full plate when swung between a magnetic field. I understand in a full plate that lenz's laws apply to try to oppose the entry and attract it but i don't know how the slit plates work. There is also something about Eddy currents which I also don't understand.
Thank you

[jakesilove]

Hi we just did "Lenz's Law on Moving Conductors (Sheets) and i am really confused as to how a metal plate with slits has a slower stopping motion than a full plate when swung between a magnetic field. I understand in a full plate that lenz's laws apply to try to oppose the entry and attract it but i don't know how the slit plates work. There is also something about Eddy currents which I also don't understand.
Thank you

Hey!

If you draw a sheet of metal, and then the eddy currents, you can imagine them like great big circles. Lots and lots of circles of electrons are moving around the sheet, and that movement of electrons creates the opposing magnetic field.

However, if a sheet of metal has slits in it, then the eddy currents themselves must get smaller. Draw a sheet with slits in it, and try to draw some circles to represent the eddy currents. They just can't be as big; they don't have enough space! So, the eddy currents are literally 'weaker', and so create a weaker magnetic field, which opposes the movement less.

It's all about the physical space that the eddy currents (ie. electrons) have to travel. Does that make sense?

[Bubbly_bluey]

It's all about the physical space that the eddy currents (ie. electrons) have to travel. Does that make sense?

Yes thank you. but quick question: are eddy currents generated to oppose the metal plates entering the magnetic field like induced current?

[jamonwindeyer]

Yes thank you. but quick question: are eddy currents generated to oppose the metal plates entering the magnetic field like induced current?

You got it

[bsdfjnlkasn]

Hey sorry if this is a really broad/silly question, but why don't satellites fall back to Earth?

Any explanations/diagrams would be greatly appreciated 

[Maraos]

Hi,
I don't know if this has already being asked before but my question is how do you get ready for a year 12 Physics skills examination?
I have a 'skills' examination this Friday (3rd of March) on Ideas to implementation and I'm not really sure how I should spend my time

My exam notification is also very vague (probably on purpose) it states;
Work covered:
All work during practical lessons. See also the above skills outcomes from the syllabus
Format:
The exam will have 5 minutes reading time and 45 minutes working time. The exam will consist of two parts; an information sheet and question section totaling 35 marks. 


Any advice or help will be greatly appreciated!
Thanks!

[Maraos]

Hey sorry if this is a really broad/silly question, but why don't satellites fall back to Earth?

Any explanations/diagrams would be greatly appreciated 

Satellites don't fall back to earth due to their extremely high velocities. This is the same reason why the moon doesn't crash into the earth, because it is in an orbit around another celestial body. Even though the gravity of Earth has an influence on the satellite and is pulling it towards the center the satellite has enough velocity to maintain an orbit. Think about shooting a cannon on-top of a very big mountain, it will travel some distance but then eventually fall. However, with enough velocity the cannon ball will continually circle the planet . So in a sense a satellite is actually falling to earth, it just has enough velocity to continually miss the atmosphere.

[jamonwindeyer]

Hi,
I don't know if this has already being asked before but my question is how do you get ready for a year 12 Physics skills examination?
I have a 'skills' examination this Friday (3rd of March) on Ideas to implementation and I'm not really sure how I should spend my time

My exam notification is also very vague (probably on purpose) it states;
Work covered:
All work during practical lessons. See also the above skills outcomes from the syllabus
Format:
The exam will have 5 minutes reading time and 45 minutes working time. The exam will consist of two parts; an information sheet and question section totaling 35 marks. 


Any advice or help will be greatly appreciated!
Thanks!

Hey! Thanks heaps for your awesome answer to the above question - Couldn't have answered it better myself

So for your skills task, I recommend you jump to Page 38 of the syllabus and have a bit of a read - That's the stuff that will be assessed (it could be the stuff on your notification, and probably is all there, but just in case). It's a bit of a mish-mash of stuff, but think things like:

- Identifying variables
- Proposing experiment designs/improvements
- Reliability, accuracy, validity
- Graphing (especially lines of best fit)
- Using equipment properly
- Research skills (is a source reliable or not and why?)

These are always tough to prepare for, but I'd spend my time going over the notes for all the practical tasks you've done for I2I so far - Understand how they work and why they work in quite a bit of detail. Read over any practical reports you've written in the last 12 months to re-familiarise with key concepts - Reliability, accuracy, variables, etc. Besides that, unless you were given a sample task (which if not you may be able to find here, not sure) then there isn't much else you can do!!

I hope that helps, at least a little - Good luck!

[Maraos]

Hey! Thanks heaps for your awesome answer to the above question - Couldn't have answered it better myself

So for your skills task, I recommend you jump to Page 38 of the syllabus and have a bit of a read - That's the stuff that will be assessed (it could be the stuff on your notification, and probably is all there, but just in case). It's a bit of a mish-mash of stuff, but think things like:

- Identifying variables
- Proposing experiment designs/improvements
- Reliability, accuracy, validity
- Graphing (especially lines of best fit)
- Using equipment properly
- Research skills (is a source reliable or not and why?)

These are always tough to prepare for, but I'd spend my time going over the notes for all the practical tasks you've done for I2I so far - Understand how they work and why they work in quite a bit of detail. Read over any practical reports you've written in the last 12 months to re-familiarise with key concepts - Reliability, accuracy, variables, etc. Besides that, unless you were given a sample task (which if not you may be able to find here, not sure) then there isn't much else you can do!!

I hope that helps, at least a little - Good luck!

Thanks for the advice!
The notification does list some syllabus outcomes so I will go back and have a look at them.
After that i guess ill just have to hope for the best   

[jamonwindeyer]

Thanks for the advice!
The notification does list some syllabus outcomes so I will go back and have a look at them.
After that i guess ill just have to hope for the best   

Unfortunately that's about all you can do! Very hard to prep for skills tests without samples - Not much more you can practice with besides drawing graphs of random data sets 

[beau77bro]

Someone please help I don't know how to even approach this/ think about it

[kiwiberry]

Someone please help I don't know how to even approach this/ think about it

(Image removed from quote.)

So this question is addressing the relativity of simultaneity!
Captain Y is in the same frame of reference as the lasers, so will see them hit at the same time. This rules out C and D
Captain X is moving with respect to the lasers, and so is in a different frame of reference. Ok, the question is a bit unclear because technically Captain X would see laser 1 hit before laser 2 if the lasers were fired after Captain X had flown past, because he'll be sitting closer to laser 1 no matter what. But, assuming Captain X was in the middle of the two lasers when they were fired (like in the train thought experiments), because the spaceship is moving at 0.5c left, Captain X will move closer to laser 1 and further away from laser 2 before they strike. Therefore, due to the constancy of the speed of light, the light from laser 1 will travel a shorter distance and reach Captain X before laser 2. So the answer should be A

[beau77bro]

Wow thankyou kiwi. But wait how is laser 1 gonna hit first. He's moving away from it but the ship isn't? Like the lasers are perpendicular to his velocity, isn't it different to the thought experiment? I'm just a tad confused but I don't get how his motion factors into the lights distance travelled when they aren't in the same plane.

[jamonwindeyer]

Wow thankyou kiwi. But wait how is laser 1 gonna hit first. He's moving away from it but the ship isn't? Like the lasers are perpendicular to his velocity, isn't it different to the thought experiment? I'm just a tad confused but I don't get how his motion factors into the lights distance travelled when they aren't in the same plane.

The lasers will definitely strike the ship at the same time with respect to Captain Y. But here's the issue - The Captain of X will only see the lasers hit the ship once the light from the point of impact reaches him. The scenario is literally the same as the thought experiment - Instead of letting off fireworks at either end, you have laser explosions! It's acknowledging that the Captain of X doesn't see the laser strikes as they happen, but once the light from those explosions reaches him, that is the tricky bit.

The other reason the lasers don't hit at the same time? It's not an option - In questions like this, if you aren't totally sure of the correct answer, sometimes you just have to go with the most sensible answer! It will often get you out of trouble