HSC Physics: Suggested Answers and Discussion

[Neutron]

And also, this is probably really dumb for multiple choice question 8, the option D had more coils which means that the length of the wire is longer right? And the longer the wire, the greater the resistance.. Since V=IR and V is constant, a greater R would result in a lower I which means the galvanometer would deflect less wouldn't it? Idk whether the greater rate of change of magnetic flux is enough to exceed this (by doubling the velocity) which is why I chose option C :/ Is that some poor logic i had going on in the exam hahahah

[jamonwindeyer]

How well do you think we needed to explain the 3 technologies question? Cause my mind blanked and the only one i could think of was Maglev trains (discovery being superconductors) but I just said that they provided high speed transportation for society through superconductive magnets without explaining the specifics :O (i don't actually know the specifics, damn my brain couldn't function during that exam)

I think the big thing was the Discovery, not so much how it is applied!

And also, this is probably really dumb for multiple choice question 8, the option D had more coils which means that the length of the wire is longer right? And the longer the wire, the greater the resistance.. Since V=IR and V is constant, a greater R would result in a lower I which means the galvanometer would deflect less wouldn't it? Idk whether the greater rate of change of magnetic flux is enough to exceed this (by doubling the velocity) which is why I chose option C :/ Is that some poor logic i had going on in the exam hahahah

I was debating this myself!! Your reasoning is correct, I think it is definitely valid, and further because more coils equal less current in a transformer!

Tbh, I'm yet to fully 100% commit to D as the solution. I totally understand your choice of C. I just think D is the more likely choice (happy to be convinced otherwise if anyone has any thoughts!)

PS - Congrats on getting to 100 posts!

[Aliceyyy98]

Hey for the question on three technilogies, it asked HOW the discovery led to them, so we would have to mention how the discovery is applied right?

[jamonwindeyer]

Hey for the question on three technilogies, it asked HOW the discovery led to them, so we would have to mention how the discovery is applied right?

This is true! Hmm, how many lines did you have... 14! So you'd have to be brief in that effect. It seems like they want a "This is the discovery that was made and this is how it was made. This principle is applied in the technology in this way." Repeat 3 times.

I'd have written something like this for the generator, for example:

Faraday's experiments, which consisted of exposing coils to changing magnetic fields, established the idea of electromagnetic induction (the generation of an EMF when exposed to changing magnetic flux). This lead to the development of the electric generator, which uses induction to convert the kinetic energy of a rotor to electrical energy for external use.

Or, something like that. I interpret the question as needing to specifically mention HOW the discovery was made, because that is HOW it lead to the development of the technology. Then of course, as you say, a somewhat detailed mention of its application.

This is a weird question though; super broad, unlike anything I've seen in a Physics paper for quite a while!

EDIT: There is more than one way to skin a cat. Not taking my exact approach doesn't necessarily mean you can't score top marks!

[Aliceyyy98]

This is true! Hmm, how many lines did you have... 14! So you'd have to be brief in that effect. It seems like they want a "This is the discovery that was made and this is how it was made. This principle is applied in the technology in this way." Repeat 3 times.

I'd have written something like this for the generator, for example:

Faraday's experiments, which consisted of exposing coils to changing magnetic fields, established the idea of electromagnetic induction (the generation of an EMF when exposed to changing magnetic flux). This lead to the development of the electric generator, which uses induction to convert the kinetic energy of a rotor to electrical energy for external use.

Or, something like that. I interpret the question as needing to specifically mention HOW the discovery was made, because that is HOW it lead to the development of the technology. Then of course, as you say, a somewhat detailed mention of its application.

This is a weird question though; super broad, unlike anything I've seen in a Physics paper for quite a while!

EDIT: There is more than one way to skin a cat. Not taking my exact approach doesn't necessarily mean you can't score top marks!

Thank you Jamon!! One more question, does school play a big role in atar calculation, or is it your hsc performance more important??

[RuiAce]

Thank you Jamon!! One more question, does school play a big role in atar calculation, or is it your hsc performance more important??

Your own cohort's performance decides how your internal marks get aligned. But only your own cohort; previous cohorts are useless in this calculation.

And moderation is dependent on your entire cohort's performance in the final exam

[hammyhtk]

Hi guys, regarding Q23b shouldnt the direction of the magnetic field be out of the page inorder for the force to be up the page so that the electron travels undeflected, or am I really confused?

[bethjomay]

Hi guys, regarding Q23b shouldnt the direction of the magnetic field be out of the page inorder for the force to be up the page so that the electron travels undeflected, or am I really confused?

I got that too! But I was unsure about it.

[jamonwindeyer]

Hi guys, regarding Q23b shouldnt the direction of the magnetic field be out of the page inorder for the force to be up the page so that the electron travels undeflected, or am I really confused?

I got that too! But I was unsure about it.

Not quite! The electric field is going INTO the page, meaning the force on the electron is OUT of the page! I think you guys might have thought the initial field was a magnetic field, not an electric field?

[bethjomay]

Not quite! The electric field is going INTO the page, meaning the force on the electron is OUT of the page! I think you guys might have thought the initial field was a magnetic field, not an electric field?

Ah, ok. I got that it was an electric field I just couldn't visualise how the field would effect it as I'd never dealt with an electric field in or out of the page, only down or up, so I just inferred the deflection like you would for a magnetic field. :/

EDIT: I am now realising the outward deflection is actually quite obvious due to the nature of an electric field and kicking myself for not noticing

[Ahbelle]

For 25 A, how do you know using only the graphs that the relationship shown by team A is 'inverse-square' not simply inverse?

[bethjomay]

For 25 A, how do you know using only the graphs that the relationship shown by team A is 'inverse-square' not simply inverse?

One way we can tell is that the graph got exponentially steeper as the distance approached zero! The curve on an 'inverse' graph would be something in the form y = 1/x which would be the same in the in the x and y directions. Someone please correct me if I'm wrong but I hope that made sense

[jamonwindeyer]

Ah, ok. I got that it was an electric field I just couldn't visualise how the field would effect it as I'd never dealt with an electric field in or out of the page, only down or up, so I just inferred the deflection like you would for a magnetic field. :/

Ahh fair enough! Yeah, electric fields are even simpler, just follow the direction of the field (or opposite for an electron)

All good! If you calculated the magnitude correctly you'll still get most of the marks

For 25 A, how do you know using only the graphs that the relationship shown by team A is 'inverse-square' not simply inverse?

Well I suppose you can immediately jump to that conclusion because Newton's Law of Universal Gravitation is inverse square in nature. Qualitatively from the graph, see Beth's explanation above (thanks Beth!). Admittedly, I probably wouldn't spot it without knowing that we are talking about gravity

[PunjanTriv]

Hey Jamon!

We did question 10 in class and somehow our teacher said the correct answer is B. Our teacher said:

As we know the train is moving towards the right, the front door is now further away and the back door is closer. As the light is turned on the light travels at the same speed and same direction, the light will eventually reach door W first. Therefore W opens before Z.

I know you are right as well.

So the answer can be either C or B.
But which one is more correct?

Thanks

[jamonwindeyer]

Hey Jamon!

We did question 10 in class and somehow our teacher said the correct answer is B. Our teacher said:

As we know the train is moving towards the right, the front door is now further away and the back door is closer. As the light is turned on the light travels at the same speed and same direction, the light will eventually reach door W first. Therefore W opens before Z.

I know you are right as well.

So the answer can be either C or B.
But which one is more correct?

Thanks

Hey Punjan! Welcome to the forums!

Your teacher is mistaken. B is incorrect.

The key in noticing why is emphasising that we are talking about what the passenger observes. The observer, in their frame of reference, sees a light source at fixed distance from two doors. So to the observer on the train, they open simultaneously.

Your teachers analysis only works for someone observing from outside the train, standing on a platform (for example). They see the back of the train catch up, so THEY will see the train door at the back open first. But the observer on the train sees them open at the same time.

The Wikipedia Article actually does a good job showing this! Scroll down to the train-platform thought experiment!

I hope this makes sense!