HSC Physics Question Thread

[jamonwindeyer]

HIHI
dumbass me is still struggling to understand the inconsistencies of the classical theory's interpretation of blackbody radiation and the UV catastrophe so far i know that they thought that emission was dependent on frequency, and that energy is absorbed is continuous ( that is, can occur at any amount and increases as wavelength becomes shorter except this true, but only applies to longer wavelengths)

could someone directly pinpoint and outline specifically ALL the things that were wrong with it?

cheers

Hey! You've pretty much spotted the two big issues, you won't need much else in the HSC! They thought intensity was related to frequency through a law called Rayleigh Jeans Law, which as you say, worked for longer wavelengths but started breaking down for shorter ones. Note that this classical theory also violated the conservation of energy - You can't have intensity (and thus, energy) approaching infinity at short wavelengths. That makes no sense. The idea of quantised energy was then the eventual solution

Btw, definitely not a dumbass, this is tough stuff! And it seems you've got a solid understanding - Is anything particularly confusing you?

[jamonwindeyer]

What exactly is magnetic flux and magnetic flux density?
Still remain somewhat confused from this dot point.
From my understanding, magnetic flux= number of magnetic field lines
                                       magnetic flux density= number of magnetic field lines per unit area
So, if you were given a question to compare two coils in a magnetic field, would you literally count the amount of lines that run through the coil?
Is magnetic flux density the same as the strength of a magnetic field?
Thanks

You are correct on every single point! note though that magnetic flux does have a more rigorous mathematical definition than "the number of field lines." The field lines are just an easy way of representing magnetic flux, and we usually associate one line to \(1\text{Wb}\) of flux when we use it

And yep, flux density is just flux per unit area, and that is how we define the strength of a magnetic field. Example, the earth's magnetic field, a butt tonne of magnetic flux, but low density - Hence, weak field

[JeffChiang]

You are correct on every single point! note though that magnetic flux does have a more rigorous mathematical definition than "the number of field lines." The field lines are just an easy way of representing magnetic flux, and we usually associate one line to \(1\text{Wb}\) of flux when we use it

And yep, flux density is just flux per unit area, and that is how we define the strength of a magnetic field. Example, the earth's magnetic field, a butt tonne of magnetic flux, but low density - Hence, weak field

Ahh right. Thanks for the clarification Jamon. It just seemed really confusing to me how simplified and undetailed the concepts are but I get it now.

[jamonwindeyer]

Ahh right. Thanks for the clarification Jamon. It just seemed really confusing to me how simplified and undetailed the concepts are but I get it now.

Welcome to HSC Physics nah I totally get it, it's almost deceptive in how simplified it is - Always happy to give the extra little bit of knowledge if it helps

[RuiAce]

Welcome to HSC Bullshitland

I think that's better Jamon

[jamonwindeyer]

I think that's better Jamon

The resentment is stroooooong

[seventeenboi]

Hey! You've pretty much spotted the two big issues, you won't need much else in the HSC! They thought intensity was related to frequency through a law called Rayleigh Jeans Law, which as you say, worked for longer wavelengths but started breaking down for shorter ones. Note that this classical theory also violated the conservation of energy - You can't have intensity (and thus, energy) approaching infinity at short wavelengths. That makes no sense. The idea of quantised energy was then the eventual solution

Btw, definitely not a dumbass, this is tough stuff! And it seems you've got a solid understanding - Is anything particularly confusing you?

ahhh okok thank you!!! glad to see that i'm on the right track! it's just that the entire dotpoint 2 is a little convoluted at times, but i'll keep working on it yay

[AJ123]

How to nail those 5-7 markers and score in the highest band for those qs?

[winstondarmawan]

Would appreciate help with Q1. I got 8ms^-1, but apparently the answer is A. TIA
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/19619126_1816906788625778_904743421_o.jpg?oh=0192829702f1c9aed574feea2a20b347&oe=5961D4B2

[jamonwindeyer]

How to nail those 5-7 markers and score in the highest band for those qs?

Hey! Big question, but a few tips:

- You need to know your syllabus, meaning, when they give you that one sentence request for information, you know the syllabus well enough to know exactly the information they want.
- Use your jargon; the proper terminology lets you express yourself more succinctly and communicate your knowledge to the marker more obviously. Make revision of these key terms an integral part of your study routine!
- Lots of practice, obviously
- Respond to the verb - When asked for a judgement, give one. When asked for an explanation, be sure to link the effect of one thing to the cause of the text. Be efficient!

There's only a limited number of 5-7 markers they can ask, aim to have practiced all of them before exam time!

[pikachu975]

Would appreciate help with Q1. I got 8ms^-1, but apparently the answer is A. TIA
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/19619126_1816906788625778_904743421_o.jpg?oh=0192829702f1c9aed574feea2a20b347&oe=5961D4B2

Your answer looks right to me.

[jamonwindeyer]

Would appreciate help with Q1. I got 8ms^-1, but apparently the answer is A. TIA
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/19619126_1816906788625778_904743421_o.jpg?oh=0192829702f1c9aed574feea2a20b347&oe=5961D4B2

Your answer looks right to me.

Ditto here, perhaps the answers are off?

[winstondarmawan]

Ditto here, perhaps the answers are off?

Thought so... just found it weird bc that was from James Ruse. Thanks guys!

[winstondarmawan]

Hello! Need help with the following, TIA.
https://scontent-syd2-1.xx.fbcdn.net/v/t35.0-12/19808040_1265016066957247_1528084618_o.png?oh=e944fbaf2f5d58e0322503ffcea055db&oe=59633739

[jamonwindeyer]

Hello! Need help with the following, TIA.

Hey! My bet here would be that the answer is C -> Mostly because it doesn't really make much sense. DC input proportional to voltage - What? The wording seems off, so that would be my pick. Note that the spring is vital to make sure the pointer doesn't just spin wildly, the plane of the coil is always parallel to the field which removes any variation as it spins, and the area needs to be constant for the same reason. So, pretty sure it is C