HSC Physics Question Thread

[S200]

Feel free to spam the thread! Or, create a new thread, asking people how they're finding Physics! Or, private message each other! Or, chat on each other's profiles! This is your forum as much as ours

Thanks Jake....
I might do the second...
How do you create a new thread??

[jamonwindeyer]

A person throws an object of 10kg upwards at 0.5ms^-1 on Earth's surface

Determine the force he has to apply on the object
Is it right to consider the acceleration the person has to exert on the object to be 10.3ms^-2 upwards? If not, whats the proper way to figure out this question? Thanks

Hey! So this question feels a little off to me, because it's a little vague. Do you mean \(0.5\text{ms}^{-2}\), so as in an acceleration? Or is that number an initial velocity? Just feels a little off to me - Perhaps snap a picture of the question?

[johnk21]

Can someone please help me with this medical physics question.
Thanks in advance.

[jamonwindeyer]

Can someone please help me with this medical physics question.
Thanks in advance.

Hey! So basically this question is in four parts:

- Why a scan is urgent: This should be clear, they are bleeding from the head! You could go into stuff about how doing it quickly means you are more likely to spot where it is coming from, but really, pretty much anything sensible works here. You'd get a mark for it.
- Drawbacks of CT scans - You'd focus on heavy exposure to ionising radiation, imo. There are others, but this is the biggest.
- Drawbacks of MRI - Although better at visualising soft tissues (and so better at detecting this bleed, most likely), and don't involve ionising radiation, MRI's are far more expensive and usually take longer to perform/more preparation.
- Make the choice - There's no correct answer here, both would work! Just make a choice and justify your answer

Does this help?

[johnk21]

Hey! So basically this question is in four parts:

- Why a scan is urgent: This should be clear, they are bleeding from the head! You could go into stuff about how doing it quickly means you are more likely to spot where it is coming from, but really, pretty much anything sensible works here. You'd get a mark for it.
- Drawbacks of CT scans - You'd focus on heavy exposure to ionising radiation, imo. There are others, but this is the biggest.
- Drawbacks of MRI - Although better at visualising soft tissues (and so better at detecting this bleed, most likely), and don't involve ionising radiation, MRI's are far more expensive and usually take longer to perform/more preparation.
- Make the choice - There's no correct answer here, both would work! Just make a choice and justify your answer

Does this help?

yes thanks so much!

[Kle123]

Could anyone help me understand why the theory that energy is quantised fixed the ultraviolet catastrophe? THANK YOU

[jakesilove]

Could anyone help me understand why the theory that energy is quantised fixed the ultraviolet catastrophe? THANK YOU

Hey! Simple answer is that you don't need to understand this. The important thing is: Planck sees the Ultraviolet Catastrophe. Planck makes up some Maths to explain the Ultraviolet Catastrophe, within which energy is quantised. He thought this was just a mathematical trick, however later Einstein would show that this 'trick' is actually how real life works!

Not in any way a satisfying answer, but the correct one for the HSC

[katnisschung]

why is it with increasing frequency there is increasing energy for an em wave?

[jamonwindeyer]

why is it with increasing frequency there is increasing energy for an em wave?

This is the old 'classical' way of considering EM waves, based on Rayleigh Jeans Law. Once you consider waves in terms of quanta, that is no longer necessarily the case!! You can read this guide for a bit of an explanation why

[katnisschung]

so i don't fully understand how hertz found the wavelength.
my teacher was talking about him being able to locate the antinodes?
this is the paragraph i can't understand from the notes is got

"he found the wavelength by reflecting the waves back towards the emitter by using a piece of metal.
this set up a standing wave pattern?? between the emitter and reflector. He used (as a probe)
another detecting loop, he was able to locate the antinode. Sparking ocurred best at these places. From the
spacing of the antinodes, he worked out the wavelength.

i only understand it rudimentary term... he superimposed two waves, one directly sent
from the source to detector and another sent from the source to be reflected by a metal plate
and then the two superimpose and he somehow studied the interference patterns and found the wavelength.

[itssona]

Heey

If i have a parallel circuit how wpuld i find voltage across a particular resistor which lies on the series branch?

[S200]

Could you give us an image??
I would presume you would still use the 1/Rt = 1/R1+1/R2 etc...

[itssona]

Could you give us an image??
I would presume you would still use the 1/Rt = 1/R1+1/R2 etc...

Oih okay makes sense thank youuu

If i have a current vs voltage graph then do i find R by finding the slope and then inverse?

Also if its not linear then do we use tangent?

Mod Edit: Post merge

[jakesilove]

so i don't fully understand how hertz found the wavelength.
my teacher was talking about him being able to locate the antinodes?
this is the paragraph i can't understand from the notes is got

"he found the wavelength by reflecting the waves back towards the emitter by using a piece of metal.
this set up a standing wave pattern?? between the emitter and reflector. He used (as a probe)
another detecting loop, he was able to locate the antinode. Sparking ocurred best at these places. From the
spacing of the antinodes, he worked out the wavelength.

i only understand it rudimentary term... he superimposed two waves, one directly sent
from the source to detector and another sent from the source to be reflected by a metal plate
and then the two superimpose and he somehow studied the interference patterns and found the wavelength.

You DEFINITELY don't need to know this stuff. DEFINITELY. All you (may) need to know is that he WAS investigating wavelength. Basically, found found areas of constructive and destructive interference, and back calculated the necessary wavelengths to cause that. Seriously, don't bother learning this stuff; no need to overcomplicate an already difficult topic area

[jamonwindeyer]

If i have a current vs voltage graph then do i find R by finding the slope and then inverse?

Yep! Gradient would be \(\frac{I}{V}\), and by Ohm's Law resistance is \(\frac{V}{I}\), so take the reciprocal

Also if its not linear then do we use tangent?

If the IV characteristics of a resistance are non-linear that means it is non-ohmic, meaning it doesn't obey Ohm's Law in the simplest sense. You can do resistance as the tangent to the curve if you want to, but you'll never touch that in HSC Physics (because it isn't a Calculus course)