HSC Physics Question Thread

[jamonwindeyer]

can anyone explain why in 2009 Q21 (a) the answer is X?? how do we know which way to current is going in order to see that the force on X is up? thanks
https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2009exams/pdf_doc/2009-hsc-physics.pdf

Hey! As above, the battery is labelled just below the coil (though in a really non obvious spot tbh). Even without the labels, when a battery is represented with the two lines like that, the longer line is always the positive terminal. Conventional current flows from positive to negative, so out of the page on Side X

From there, right hand slap rule. Current (thumb) out of the page, magnetic field to the right, force is therefore upwards

[itssona]

can someone help with 2010 q24 please
The answer says that Earth & Sun exert a gravitational field which creates a centripetal force (?) that keeps JWsT in orbit but how does this answer the question :/

thanks

[jamonwindeyer]

can someone help with 2010 q24 please
The answer says that Earth & Sun exert a gravitational field which creates a centripetal force (?) that keeps JWsT in orbit but how does this answer the question :/

thanks

Hey! Are you referencing the NESA sample answer? I think it answers the question:

Both the Sun and the Earth exert a force on the JWST which is towards the Sun. Therefore the
centripetal force on the JWST is greater than that produced by the Sun alone. This means that
the orbital speed of the JWST around the Sun is greater than it would be if the Sun alone were
producing the centripetal force on the JWST and therefore the period is less than would be
predicted from Kepler’s law of periods, given that its orbital radius is greater than that of the
Earth.

To expand on the sample answer - We understand that the combined gravitational attraction of the sun and the earth produces a larger centripetal force than what the earth experiences from the sun alone. According to:



An increase in force will correspond to an increase in velocity. As F goes up, v goes up. This allows it to contradict Kepler's Law of Periods. Even though its orbital radius is slightly greater than that of earth, it can still orbit with the same orbital period as the earth, since it is moving faster than it would normally be moving at that orbital radius

[itssona]

Hey! Are you referencing the NESA sample answer? I think it answers the question:

Both the Sun and the Earth exert a force on the JWST which is towards the Sun. Therefore the
centripetal force on the JWST is greater than that produced by the Sun alone. This means that
the orbital speed of the JWST around the Sun is greater than it would be if the Sun alone were
producing the centripetal force on the JWST and therefore the period is less than would be
predicted from Kepler’s law of periods, given that its orbital radius is greater than that of the
Earth.

To expand on the sample answer - We understand that the combined gravitational attraction of the sun and the earth produces a larger centripetal force than what the earth experiences from the sun alone. According to:



An increase in force will correspond to an increase in velocity. As F goes up, v goes up. This allows it to contradict Kepler's Law of Periods. Even though its orbital radius is slightly greater than that of earth, it can still orbit with the same orbital period as the earth, since it is moving faster than it would normally be moving at that orbital radius

shh makes sense!! thank you jamon

[itssona]

kinda confused - what does the rotor do in an induction motor? I know it isn't connected to the power source and instead it creates current but what is its role? thanks

[jamonwindeyer]

kinda confused - what does the rotor do in an induction motor? I know it isn't connected to the power source and instead it creates current but what is its role? thanks

It is designed as a place for the induced currents to flow in response to the changing magnetic field generated by the stator! The rotor then spins due to the motor effect to do some sort of mechanical work. It's the exact same as any other motor, except the source of current is electromagnetic induction, rather than a direct electrical supply

[philgee]

Hello, I am unsure how to plan out my answer for this question.

"Superconductors are the future of communication technology. Either we begin to use them every day, or we fade into technological stasis."

Assess this statement with reference to at least 2 specific applications of superconductors and the Advantages and Disadvantages of their use. (7M)

[jamonwindeyer]

Hello, I am unsure how to plan out my answer for this question.

"Superconductors are the future of communication technology. Either we begin to use them every day, or we fade into technological stasis."

Assess this statement with reference to at least 2 specific applications of superconductors and the Advantages and Disadvantages of their use. (7M)

Hey philgee! I like this question. So I'd start by filling in the specific things it requests:

- Application #1
- Application #2
- Advantages
- Disadvantages

The only other real thing it wants is an assessment/judgement, and that would probably go at the end. So in general the response looks like:

Superconductors are _____. They are currently used in EXPLAIN APPLICATION ONE. They are also used in EXPLAIN APPLICATION TWO. Generally, superconductors are advantageous because ________. Their limits include _______. Overall, superconductors are MAKE YOUR JUDGEMENT.

From there it is honing, and perhaps doing things like tables/dot points, decide how best to present it is that helpful? Is all the content you need for this question sitting okay for you?

[philgee]

HI Jamon,

Thank you sooooo much!!! I clearly see what the set up should be, and the mark allocation. I appreciate it.

[owidjaja]

Hey guys,
I was going through the applications of superconductors and was reading on its use in superconducting quantum interference device (SQUID) and how it's able to detect tiny magnetic fields with an insulator in between two superconducting materials. But how are they able to detect magnetic fields through the insulator?

[jamonwindeyer]

Hey guys,
I was going through the applications of superconductors and was reading on its use in superconducting quantum interference device (SQUID) and how it's able to detect tiny magnetic fields with an insulator in between two superconducting materials. But how are they able to detect magnetic fields through the insulator?

Hey!

Syllabus Answer: Not assessable, so don't worry!!

Actual Answer, very much rough because this is way out of my league: What those superconductors and the insulator form is called a Josephson Junction. These junctions can have a current flowing through them without any voltage applied, due to the quantum tunnelling of cooper pairs from one superconductor to the other. A magnetic field applied to this junction (in a specific arrangement, I think there is multiple in a SQUID?) will change the current flowing through it, and this allows super precise measurement of the field. Last sentence super waffly, I know, but that's my rough understanding of it. Try Googling the Josephson effect if you want to learn more!

But yeah, waaaaay beyond the syllabus, so don't stress

[talitha_h]

When doing the transformer prac: why is there no voltage produced when the power supply is replaced by a regular battery?

Is it simply because it lacks a fluctuating field that comes from AC power?
Thank you

[jamonwindeyer]

Is it simply because it lacks a fluctuating field that comes from AC power?
Thank you

Hey! Exactly, AA/AAA (or whatever) batteries are sources of DC power. No changing field, no induction, so no transformer

[talitha_h]

So for my assessment we are doing a transformer prac. I don't specifically know what we will be doing but we will be asked on possible sources of error and suggestions for improvement for the prac. Any help is appreciated, thanks.

[Jane20]

Hi guys can anyone pls explain the relative simultaneity for me

I am so confused.
For example suppose in a very long train that is moving at relativistic speed and fireworks are launched at both ends of the train at the same time. Which observer will see that the launching simultaneous ? The one inside the train and stands in the middle or the observer from outside ?

Thanks alot guys !!