HSC Physics Question Thread

[jamonwindeyer]

I'm sorry last question for today promise XD
So is the induced emf generated when the ammature cuts the magnet flux, and the system does not like that so it will create back emf to counter that?

Ahaha no worries! Yep that is pretty much it - The changing magnetix flux experienced by the armature is caused by the rotation, and as you say, it "doesn't like it" (Physics hates change) and an opposing emf (back emf) is induced to counteract that change

[bsdfjnlkasn]

Hey Jamon and kiwiberry!

Sorry I wasn't sure of how to quote both of your responses but I really wanted to thank you for helping me out! I am quite convinced we'll have a prac on analysing projectiles but i've taken down the extra pendulum information (which was super detailed and helpful btw  !) just in case. We only just started learning about projectiles so what do you think we could be asked to do in relation to them - probably proving their parabolic shape if subject to constant acceleration? But then how could they incorporate graphs and gradients? Also what would you do in an exam if your results were really far off the theoretical but you don't have time to change them - I guess it gives you more to talk about in the accuracy/reliability/validity sections but surely they'll have to deduct marks if it's just outright inaccurate - really hoping this doesn't happen

Also, when it comes down to asking questions on all three (accuracy/reliability/validity), would it be wise to address them sometimes together? Or are they so distinct that there is little room to join them and show how decreasing accuracy comes at the expense of decreasing validity for example. Does that make sense? I just feel like i'd run out of things to say if I had to focus on one specific thing. Are there any stand out things I should mention for each one? A google search isn't particularly helpful in this so as always, any help would be greatly appreciated!!

[helpsme]

1.Why do the atmosphere and the surface of the earth emit infa-red radiation?

2.Why does the air cool as it rises?

3.Why is so little heat transferred from the Earth's surface to its atmosphere by conduction?

[jamonwindeyer]

Hey Jamon and kiwiberry!

Sorry I wasn't sure of how to quote both of your responses but I really wanted to thank you for helping me out! I am quite convinced we'll have a prac on analysing projectiles but i've taken down the extra pendulum information (which was super detailed and helpful btw  !) just in case. We only just started learning about projectiles so what do you think we could be asked to do in relation to them - probably proving their parabolic shape if subject to constant acceleration? But then how could they incorporate graphs and gradients? Also what would you do in an exam if your results were really far off the theoretical but you don't have time to change them - I guess it gives you more to talk about in the accuracy/reliability/validity sections but surely they'll have to deduct marks if it's just outright inaccurate - really hoping this doesn't happen

Also, when it comes down to asking questions on all three (accuracy/reliability/validity), would it be wise to address them sometimes together? Or are they so distinct that there is little room to join them and show how decreasing accuracy comes at the expense of decreasing validity for example. Does that make sense? I just feel like i'd run out of things to say if I had to focus on one specific thing. Are there any stand out things I should mention for each one? A google search isn't particularly helpful in this so as always, any help would be greatly appreciated!!

Projectile questions will usually involve either something to do with their parabolic flight path, or you could even use projectile analysis to determine a value for acceleration due to gravity. They'll all be fairly similar though: Launch a projectile horizontally from a given height, measure the range (usually)

If you get a significantly (>10% error) inaccurate result, use your discussion to extrapolate as to the reasons why. Believe it or not, if you perform a valid experiment, take results correctly, analyse them correctly and discuss why they could be inaccurate, you should still perform quite well! The majority of the marks will be on your skills, there shouldn't be a heap assigned to your results actually being accurate you could of course redo the experiment if you have time, but that's a push

You can definitely discuss those three things together, though you MUST address each of them in some way. Rui wrote a great guide on how they might interrelate

[Shadowxo]

Hey Jamon and kiwiberry!

Sorry I wasn't sure of how to quote both of your responses but I really wanted to thank you for helping me out! I am quite convinced we'll have a prac on analysing projectiles but i've taken down the extra pendulum information (which was super detailed and helpful btw  !) just in case. We only just started learning about projectiles so what do you think we could be asked to do in relation to them - probably proving their parabolic shape if subject to constant acceleration? But then how could they incorporate graphs and gradients? Also what would you do in an exam if your results were really far off the theoretical but you don't have time to change them - I guess it gives you more to talk about in the accuracy/reliability/validity sections but surely they'll have to deduct marks if it's just outright inaccurate - really hoping this doesn't happen

Also, when it comes down to asking questions on all three (accuracy/reliability/validity), would it be wise to address them sometimes together? Or are they so distinct that there is little room to join them and show how decreasing accuracy comes at the expense of decreasing validity for example. Does that make sense? I just feel like i'd run out of things to say if I had to focus on one specific thing. Are there any stand out things I should mention for each one? A google search isn't particularly helpful in this so as always, any help would be greatly appreciated!!

Just adding to jamonwindeyer (from a VCE course perspective)
Often you'll have to resolve the speed into it's different components, and use this to find a variable. Some common ones are how long it's in the air, how far it travels horizontally, the speed it hits the ground at, etc. If you can resolve the speed into it's components and use the basic physics equations it should be fairly straightforward. They may also ask questions such as "when tested, the projectile didn't travel as far as calculated, explain why" - air resistance, and other similar questions. Overall I found projectiles straightforward so you should be fine. Good luck

[jamonwindeyer]

Just adding to jamonwindeyer (from a VCE course perspective)
Often you'll have to resolve the speed into it's different components, and use this to find a variable. Some common ones are how long it's in the air, how far it travels horizontally, the speed it hits the ground at, etc. If you can resolve the speed into it's components and use the basic physics equations it should be fairly straightforward. They may also ask questions such as "when tested, the projectile didn't travel as far as calculated, explain why" - air resistance, and other similar questions. Overall I found projectiles straightforward so you should be fine. Good luck

Just giving this the HSC Tick of Approval: All definitely directly relevant

[f_tan]

Is the first hypothesis/experiment about the aether model, or is it Einstein's thought experiments for his Theory of Special Relativity?



Thanks!

[lsong]

Hi,
I have 2 questions that I think are pretty general, but I'm not sure what to talk about.

1) Contrast the operation of a galvanometer with that of a simple generator (2)

For this question, I feel like two points need to be made. One of those could be that one requires a current to function while the other creates the current. For the second point would it be okay to contrast the structure?

2) Manufacturers state that induction cook tops can only be used with saucepans made from iron and purchasers are advised to use a refrigerator magnet to test their saucepans.

Since currents can be induced in metals other than iron, discuss the reasons for designing induction cook tops that require iron based saucepans. (3)

For this question, I know that iron is conductive but has high resistance which means the eddy currents collide with the lattice structure of the iron. I also know that iron is ferromagnetic, but I'm not sure how this could be related.

Any help would be great thanks!

[jamonwindeyer]

Is the first hypothesis/experiment about the aether model, or is it Einstein's thought experiments for his Theory of Special Relativity?

(Image removed from quote.)

Thanks!

Hey! I'd say the Aether (and Michelson and Morley's inability to detect it) was the observation that raised the problem, and Einstein's Special Theory of Relativity was the new hypothesis. The initial experiments (thought experiments) provided some validation for the model, which is why it was adopted so quickly, but it was the real world experiments conducted in the late 20th/early 21st century which really hammered it home

[jamonwindeyer]

Hi,
I have 2 questions that I think are pretty general, but I'm not sure what to talk about.

1) Contrast the operation of a galvanometer with that of a simple generator (2)

For this question, I feel like two points need to be made. One of those could be that one requires a current to function while the other creates the current. For the second point would it be okay to contrast the structure?

2) Manufacturers state that induction cook tops can only be used with saucepans made from iron and purchasers are advised to use a refrigerator magnet to test their saucepans.

Since currents can be induced in metals other than iron, discuss the reasons for designing induction cook tops that require iron based saucepans. (3)

For this question, I know that iron is conductive but has high resistance which means the eddy currents collide with the lattice structure of the iron. I also know that iron is ferromagnetic, but I'm not sure how this could be related.

Any help would be great thanks!

Hey hey!

For the first one, I like the way you think! Definitely a peculiar question, I'd say your planned answer would work really well

For the second one, you've also got it. The main idea is that iron is ferromagnetic (the resistance is important too but not as much I don't think). As a ferromagnetic substance, iron is very susceptible to magnetisation, which (basically) also makes it very susceptible to eddy current flow. Explaining the specifics of ferromagnetism properly is beyond the syllabus - It is a quantum mechanical thing - But it should make intuitive sense. Ferromagnetic substance means easily magnetised, meaning easily affected by magnetic field. Therefore, the eddy currents will form more easily and thus dissipate more heat

So my answer would focus on iron being ferromagnetic, and thus, that the effects of induction cooktops are more pronounced. This would involve a brief mention of how an induction cooktop works in the first place

[lsong]

Thanks for the help Jamon! 

[bsdfjnlkasn]

Hey I've been asked to "calculate the distance a satellite must be from Earth to be in geostationary orbit" how do even go about solving this? Any help would be greatly appreciated

[Syndicate]

Hey I've been asked to "calculate the distance a satellite must be from Earth to be in geostationary orbit" how do even go about solving this? Any help would be greatly appreciated

T = 24 hours (a geostationary satellite is one which orbits the earth whilst remaining over a certain location on earth at all times.

Convert it to seconds, and use the formula: r^3 = (T^2 x GM)/4pi^2

r = the radius of the satellite from the centre of the earth. Therefore, to calculate the satellite's distance from the Earth's surface, you will need to subtract it by the radius of the Earth.

[Bubbly_bluey]

Hi! I'm having a trouble understanding the answer to this question.

Initially I chose B because the galvanometer would deflect more if the current in the secondary increase by the formula. Isecondary/ Iprimary= n primary/ n secondary. And so a decrease in n secondary??

[Iminschool]

Hi! I'm having a trouble understanding the answer to this question.

Initially I chose B because the galvanometer would deflect more if the current in the secondary increase by the formula. Isecondary/ Iprimary= n primary/ n secondary. And so a decrease in n secondary??

i agree with your explanation, i reckon it is B too as it is a step-down transformer. Thus, as V decreases, I increases