HSC Physics Question Thread

[blasonduo]

I checked the excel book to help you guys out..
so it says
A - Max. energy output from human = E=hf
=hc / wavelength
= (6.626x10^-34) x( 3x10^8) / (9x10^8)
= 0.138 eV
Therefore the band gap should be less than 0.138 eV. This makes HgCdTe the best choice.

Hey! thanks for that!

I still agree with pikachu here, A is such a silly answer for the Excel book to go for.

Theres no way A would be more suited than B here

[winstondarmawan]

EDIT

19) This is MUCH easier if we rule out the incorrect ones, For A, the force of gravity is NOT negligible, as that's what keeps objects in orbit! so it is wrong. While B is true, this is not answering the question, it is just a statement.

We now have it to C or D, for C, IF the forces were to be the same, (ie F = ma) since, the question claims F is the same, while mass is different, their accelerations must be different, and well, if their accelerations are  different, how on earth can they travel at the same speed? So C is incorrect, leaving only D as the answer (if you would like me to explain why i'll be happy to!)

Yes please.

[blasonduo]

Yes please.

Sure thing! This kinda is hard to understand, so I'll see if I can explain it properly

We know that acceleration = F/m

and that gravitational force is  GmM/d^2

but as we have now defined force as F/m, we must also divide the gravitational force by m (the mass of the object)

So since we have defined acceleration as the objects force over their respective masses (the inversely proportional part of the answer!!)

And that force equalling the gravitational force, but without their respective masses. We here have explained how answer D is correct!

This is kinda tough to get your head around (and hence why I said this is best answered by removing the wrong answers) but I hope this makes sense.

If it didn't I'll happy to elaborate the confusion

[sidzeman]

The principle of relativity states that you cannot conduct any mechanical experiments within an inertial FOR to reveal if you are moving at a constant velocity or stationary. However what I dont understand is how nonintertial FOR apply to relativity

[jamonwindeyer]

What stuff about Westinghouse and Edison do we have to know? Since I think I know too much irrelevant information about this dotpoint

If you know it already keep it in the noggin! No harm in knowing a little too much

The principle of relativity states that you cannot conduct any mechanical experiments within an inertial FOR to reveal if you are moving at a constant velocity or stationary. However what I dont understand is how nonintertial FOR apply to relativity

Basically, non-inertial FOR does weird shit to relativity. And you don't need to understand anything beyond what they are, and that if you want to do anything with them you end up creating fictional forces to account for your observations. Anything beyond those two bits of knowledge is irrelevant

[sidzeman]

Basically, non-inertial FOR does weird shit to relativity. And you don't need to understand anything beyond what they are, and that if you want to do anything with them you end up creating fictional forces to account for your observations. Anything beyond those two bits of knowledge is irrelevant

Ahhh I see thank you. Also for med phys, can MRI be used to image bone? Some sources say that it image the spinal cord, but I dont see how this is possible when bone does not contain any hydrogen

[jamonwindeyer]

Ahhh I see thank you. Also for med phys, can MRI be used to image bone? Some sources say that it image the spinal cord, but I dont see how this is possible when bone does not contain any hydrogen

Spinal cord is a lovely bunch of neurons that send stuff to the rest of your body - It actually isn't a bone! There are bones around it of course

That said I think you can take an MRI of bones, not sure exactly how it works but I think it can be done! Probably targets other types of nuclei?

[Mymy409]

Hey! This was answered a few pages back!

https://atarnotes.com/forum/index.php?topic=164552.msg996472#msg996472

Here it is!

Thanks! However, it's still a bit unclear to me. Could you explain how the force doesn't change?

[jamonwindeyer]

Thanks! However, it's still a bit unclear to me. Could you explain how the force doesn't change?

So the force on a current carrying conductor is \(F=BIL\sin{\theta}\), where \(\theta\) is the angle with the field. Even as the coil rotates, the wire is always perpendicular to the field. The coil isn't, that definitely changes, but the wire is always perpendicular (\(\theta=90\))! So the size of the force doesn't change

[beau77bro]

hi, q 15 and 16 have me stumped for 2016 hsc... and also 1 - because i thought batteries need DC to reverse the reactions within the battery so that it can be used again... so how is it still AC - i get it is lowered because the phone cant take high voltages but still i just thought it would be DC.

https://educationstandards.nsw.edu.au/wps/wcm/connect/5c414559-9792-41e6-bd98-e43c9097168d/2016-hsc-physics.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-5c414559-9792-41e6-bd98-e43c9097168d-lHPDHJd

[beau77bro]

Spinal cord is a lovely bunch of neurons that send stuff to the rest of your body - It actually isn't a bone! There are bones around it of course

That said I think you can take an MRI of bones, not sure exactly how it works but I think it can be done! Probably targets other types of nuclei?

your bones do contain some water - bone marrow and all isnt just dust and most organic compounds are hydrogen based anyway? right?

[CyberScopes]

hi, q 15 and 16 have me stumped for 2016 hsc... and also 1 - because i thought batteries need DC to reverse the reactions within the battery so that it can be used again... so how is it still AC - i get it is lowered because the phone cant take high voltages but still i just thought it would be DC.

https://educationstandards.nsw.edu.au/wps/wcm/connect/5c414559-9792-41e6-bd98-e43c9097168d/2016-hsc-physics.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-5c414559-9792-41e6-bd98-e43c9097168d-lHPDHJd

For 16, the speaker thing is a generator since mechanical energy (pushing the coil) is being converted into a current. According to lenzs law, the direction of the current has to oppose the cause of induction - i.e. the force has to push to the right. Therefore, check the direction of current by using the RHPR at any point - say for example the top of the coil - and you find that for the force to push the coil to the right, the current flows through the coil from y to x. But since we're tryna find the direction in terms of the conductor, if the current continues to flow with that as a reference point, it flows from the x side of the conductor to y. So the answer is BA

Edit: I meant A not B sorry

[khadeeja_]

Hey could someone explain q20 from 2015
the answer is B

[blasonduo]

hi, q 15 and 16 have me stumped for 2016 hsc... and also 1 - because i thought batteries need DC to reverse the reactions within the battery so that it can be used again... so how is it still AC - i get it is lowered because the phone cant take high voltages but still i just thought it would be DC.

https://educationstandards.nsw.edu.au/wps/wcm/connect/5c414559-9792-41e6-bd98-e43c9097168d/2016-hsc-physics.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-5c414559-9792-41e6-bd98-e43c9097168d-lHPDHJd

Hello!

For 1) You are confusing a transformer for a rectifier A transformer only steps-up or steps-down a voltage. A rectifier changes AC to DC

15) B is outright wrong as a solar cell consists of an n-type and p-type "squished" together, light can't convert this
C is wrong because if this were true, the solar cell wouldn't work, the light adds energy for an electron to move around the external circuit.
D is wrong as its the n-type the light transfers energy to.

16) As we are moving the cone, it must be a generator. C and D are out.
Now due to Lenz's law when we push the solenoid, the solenoid will produce a NORTH pole to resist the change. From here we can figure out the direction of current (NANTI - SOCK)

and we see that it flows X to Y, so A

[beau77bro]

Hello!

For 1) You are confusing a transformer for a rectifier A transformer only steps-up or steps-down a voltage. A rectifier changes AC to DC

15) B is outright wrong as a solar cell consists of an n-type and p-type "squished" together, light can't convert this
C is wrong because if this were true, the solar cell wouldn't work, the light adds energy for an electron to move around the external circuit.
D is wrong as its the n-type the light transfers energy to.

16) As we are moving the cone, it must be a generator. C and D are out.
Now due to Lenz's law when we push the solenoid, the solenoid will produce a NORTH pole to resist the change. From here we can figure out the direction of current (NANTI - SOCK)

and we see that it flows X to Y, so A

OHHH I GET 1 - IT SAID TRANSFORMER MY BAD
16 I READ WRONG OML.

15 - WHY IS C WRONG?