HSC Physics Question Thread

[Loki98]

Thanks for the help Jamon, that was a great explanation

[Neutron]

Is Lenz's law basically irrelevant to transformers :O and rip do you guys have some spare motivation lying around

[jamonwindeyer]

Is Lenz's law basically irrelevant to transformers :O and rip do you guys have some spare motivation lying around

Lenz's Law is relevant everywhere! is there something specifically confusing you? It is a little outside the syllabus but I can try and help out? I did a decent amount on transformers last semester 

Edit: Lol, one week into uni and already procrastinating, sorry, don't think I can help there 

[Aliceyyy98]

Hi!

My teacher has been going on about triodes for the ideas to implementation topic, do we need to understand how it works? like the reverse and forward bias things, as well as base current or something!

I was really confused and was wondering if this is required for the syllabus?

Cheers

[Neutron]

Lenz's Law is relevant everywhere! is there something specifically confusing you? It is a little outside the syllabus but I can try and help out? I did a decent amount on transformers last semester 

Edit: Lol, one week into uni and already procrastinating, sorry, don't think I can help there 

Well when you're describing the formation of eddy currents within a transformer's iron core, it's not actually because of Lenz's law is it? Actually, forgive me if this is just a massive brain fart but why do eddy currents form within transformer's cores again? It's not like the eddy current is opposing the rate of change of magnetic flux so i'm like ah i'm tired

[jamonwindeyer]

Well when you're describing the formation of eddy currents within a transformer's iron core, it's not actually because of Lenz's law is it? Actually, forgive me if this is just a massive brain fart but why do eddy currents form within transformer's cores again? It's not like the eddy current is opposing the rate of change of magnetic flux so i'm like ah i'm tired

Well the currents themselves are formed as a result of Faraday's Law of induction, but yes, Lenz's Law tells us in which direction they will move! Remember, we have a changing magnetic flux due to the AC current in the primary coil, and this changing flux induces eddy currents in the core (and it is this flux which allows the new current to flow in the secondary coil too)  of course the laminations in a transformer mean that this doesn't have too much of an impact, but Lenz's Law definitely plays a big role in describing these eddy currents, they are formed to oppose the changing flux from the primary coil! 

[jamonwindeyer]

Hi!

My teacher has been going on about triodes for the ideas to implementation topic, do we need to understand how it works? like the reverse and forward bias things, as well as base current or something!

I was really confused and was wondering if this is required for the syllabus?

Cheers

Hey! This is definitely not something that is super important in the HSC Physics course, it's a little beyond the scope. A basic understanding of forward and reverse bias for PN junctions would be useful; Basically, forward bias allows current to flow, reverse bias makes it really difficult (just depends on which end of the junction is connected to the positive terminal of voltage). Essentially, it means current can only flow in a single direction.

There is a great summary of the forward and reverse bias stuff on HyperPhysics that I recommend you read! It gives a great explanation of the ideas, but it is a little complicated, let me know if you need any help with it 

The base current stuff is to do with basic transistor theory. Essentially, there are three terminals: The base, the collector and the emitter. The base current controls the current flow between the collector and the emitter. The specifics of that are definitely unimportant! A very complicated article here if you feel brave, but it is beyond what would be asked in HSC Physics, save that for tertiary electronics 

[Loki98]

Could someone please help me with these questions.
How would you explain how a transformer works using the conservation of law of energy?
Also, in the syllabus is asks to "compare the structure and function of a generator to an electric motor," when they say electric motor, do they ask for AC and DC motors?
thank you 

[MysteryMarker]

Ideas to Implementation Question:

For the fluorescence screen investigation carried out to deterimine the nature of cathode rays, why is it that this experiment can be considered as giving evidence for both the particle and wave nature of cathode rays. Like i understand that the CR's transferred their energy to the fluorescent atoms, but how do they do work?

Thanks Guys.

[RuiAce]

Ideas to Implementation Question:

For the fluorescence screen investigation carried out to deterimine the nature of cathode rays, why is it that this experiment can be considered as giving evidence for both the particle and wave nature of cathode rays. Like i understand that the CR's transferred their energy to the fluorescent atoms, but how do they do work?

Thanks Guys.

Very dumbed down, short and unorthodox answer

It could be that a transfer of energy is taking place (particle), or it could be that the cathode rays were what's glowing themselves (wave)

[jamonwindeyer]

Could someone please help me with these questions.
How would you explain how a transformer works using the conservation of law of energy?
Also, in the syllabus is asks to "compare the structure and function of a generator to an electric motor," when they say electric motor, do they ask for AC and DC motors?
thank you 

Hey Loki!

Basically with a transformer, you are never going to get an out more energy than you put in (conservation of energy). For a real transformer, the output power will always be ever so slightly less than the input, due to power losses in the transformer. The input power is equal to the output power, plus any losses in the transformer (heating, flux leakage, etc.).



The idea with this formula is that in a step up transformer, where the voltage is increased, that voltage must come from somewhere. There has to be a trade off, even if the losses aren't there. The trade off is that current decreases. The same works in reverse; if we step down the voltage, our current increases!

Summarising, the power into a transformer is close to equal to the power out of a transformer. So, if voltage goes up, current goes down. If voltage goes down, current comes up 

And yep, you need to know both AC and DC Motors/Generators for that dot point (excluding three phase induction motors) 

[conic curve]

How do I answer this question

Explain, in terms of the principle of physics involved, why it is potentially dangerous to leave loose objects on the back shelf of a car

I know it has to do with Newton's law where that if a car comes to a stop, the object starts flying (I think it's the first law) but I'm not sure how to structure this in an extended response format

Thanks

[jamonwindeyer]

How do I answer this question

Explain, in terms of the principle of physics involved, why it is potentially dangerous to leave loose objects on the back shelf of a car

I know it has to do with Newton's law where that if a car comes to a stop, the object starts flying (I think it's the first law) but I'm not sure how to structure this in an extended response format

Thanks

Hey conic! Yep, that's exactly it, Newton's 1st Law of Motion (Inertia)  in terms of structuring an answer around it, you shouldn't need an extended response, just explain what happens, why it happens (inertia), and how it is potentially dangerous (sharp objects, blunt trauma, etc)  physics responses are fairly free-form! Don't think about it too much, just put down what you know 

[Neutron]

Oh my god sorry Jamon i was thinking of something completely different!! Cause my friend drew the diagram of a transformer with the eddy currents forming the same way as the magnetic flux was travelling so I was like Anyhow, all good now!

For this 6 marker, I was wondering what key points we need to include? Thank you!!

Explain why Uranium ore is enriched for use in nuclear weapons, with reference to critical mass and neutron capture

This is a q2q question but maybe you guys would know a thing or two? :O

Thank you again!

Neutron

[jamonwindeyer]

Oh my god sorry Jamon i was thinking of something completely different!! Cause my friend drew the diagram of a transformer with the eddy currents forming the same way as the magnetic flux was travelling so I was like Anyhow, all good now!

For this 6 marker, I was wondering what key points we need to include? Thank you!!

Explain why Uranium ore is enriched for use in nuclear weapons, with reference to critical mass and neutron capture

This is a q2q question but maybe you guys would know a thing or two? :O

Thank you again!

Neutron

All good, no dramas at all no reason to apologise! I'll throw to Jake and/or diiiii for that question