HSC Physics Question Thread

[envisagator]

A statement is deemed valid when the conclusion the student draws upon follows current works or theories.

From the given statement, I see three distinct conclusions that the text draws upon;

1) Electricity is a form of energy
2) It is good for killing people
3) Its use is very limited

So in your response, you need to address each point individually and then as an overall conclusion.

Energy is the capacity to do work, electrical energy is the movement of electrons and thus contains kinetic energy. So the first statement is valid (although saying "electricity" isn't the best wording, but I'll assume that's fine )

It indeed has the ability to easily kill people, as little as 0.1 amps can stop the heart and has proven fatal. (This, however, is not assessed in HSC physics, so just acknowledging the fact that this statement holds some truth should be sufficient)

The last statement is probably the most critical aspect that cracks the validity, you should already know through the motors and generators topic, that electrical energy has huge uses. (globalisation, advanced medical equipment, more leisure through mechanical applications, etc...) use points such as these to prove that this point is indeed invalid.

Sum everything up, show that the statement has some truths, but overall does not have accurate conclusions and is thus invalid.

Hope this helps

this is fantastic, thank you very much!!!

[moq418]

For the hsc and Trials physics exam are there any questions that are going to be always ask if so please tell me what they are thanks>!!

[envisagator]

For the hsc and Trials physics exam are there any questions that are going to be always ask if so please tell me what they are thanks>!!

A good start is going through the syllabus and get confident with how the syllabus points are phrased, you should be/get comfortable with the ones that asks you to assess, discuss, justify, explain, analyse.... as the questions in exams basically come from these dot points with a few twists which require you to combine knowledge from each section. Some common questions are like: Assess the contribution of Hertz, Einstein, Plank to quantum theory, competition between Westinghouse and Edison, and those development of these or that to society/ environment. Hope this helps!!!

[envisagator]

The question is: Explain why magnetic flux is important when generating emf.
I'm having trouble phrasing the answer to this question, this is what my answer is sort off leading to: Faradays law of electromagnetic induction, then talking about how current in a circuit takes a brief moment to reach maximum or zero value resulting in a changing magnetic field (hence mag.flux) inducing an emf, is this correct?? or what should I include??

[blasonduo]

The question is: Explain why magnetic flux is important when generating emf.
I'm having trouble phrasing the answer to this question, this is what my answer is sort off leading to: Faradays law of electromagnetic induction, then talking about how current in a circuit takes a brief moment to reach maximum or zero value resulting in a changing magnetic field (hence mag.flux) inducing an emf, is this correct?? or what should I include??

This question is emphasising on Faraday's Law, but I would argue that it isn't the magnetic flux that is important, but more the change of magnetic flux. I would state Faraday's law and include the formula; I think applying the formula to the question really shows your knowledge on the topic. I would then explain how the change of magnetic flux can optimise the EMF, showing how important it really is.

I wouldn't think this would be a high mark question.

Hope this helps! Ask away if you need any clarification!

[envisagator]

This question is emphasising on Faraday's Law, but I would argue that it isn't the magnetic flux that is important, but more the change of magnetic flux. I would state Faraday's law and include the formula; I think applying the formula to the question really shows your knowledge on the topic. I would then explain how the change of magnetic flux can optimise the EMF, showing how important it really is.

I wouldn't think this would be a high mark question.

Hope this helps! Ask away if you need any clarification!

Its a 3 mark question. The problem i had was whether explaining faradays law in terms of the requirments for generating emf would give me the marks, I was thinking you had to explictly say explaing how magnetic flux generates an emf which I'm not exactly sure about. Just a bit confused!!

[blasonduo]

Its a 3 mark question. The problem i had was whether explaining faradays law in terms of the requirments for generating emf would give me the marks, I was thinking you had to explicitly say explaing how magnetic flux generates an emf which I'm not exactly sure about. Just a bit confused!!

Yep! Definitely include that in! Normally, I would coincide that with Faraday's law, but that is definitely an important part of the question!

[Mate2425]

Hi could someone please help me with understanding Forward bias and Reverse bias  in p-n junction with simple terminology and if possible the correct way to draw diagrams.

Thanks

[blasonduo]

Hi could someone please help me with understanding Forward bias and Reverse bias  in p-n junction with simple terminology and if possible the correct way to draw diagrams.

Thanks

Hey! To my knowledge, this content is beyond the scope of this course!

[jamonwindeyer]

Hi could someone please help me with understanding Forward bias and Reverse bias  in p-n junction with simple terminology and if possible the correct way to draw diagrams.

Thanks

Hey! To my knowledge, this content is beyond the scope of this course!

Indeed it is right on the edge of the course do you understand how/why the PN junction forms? If you do, that's pretty much what you need!

Remember also that reverse bias increases the size of the depletion zone in the junction, thus making it nearly impossible for current to flow through. Forward bias allows current to flow through quite easily, because the size of that depletion zone is reduced (beyond a threshold forward-bias voltage, say about 0.7V, you can have pretty much as much current as you want flowing through without any additional voltage)

Happy to elaborate on anything you need though - But yeah, blasonduo is right in that this is a little beyond what you need for the course

[Mate2425]

Indeed it is right on the edge of the course do you understand how/why the PN junction forms? If you do, that's pretty much what you need!

Remember also that reverse bias increases the size of the depletion zone in the junction, thus making it nearly impossible for current to flow through. Forward bias allows current to flow through quite easily, because the size of that depletion zone is reduced (beyond a threshold forward-bias voltage, say about 0.7V, you can have pretty much as much current as you want flowing through without any additional voltage)

Happy to elaborate on anything you need though - But yeah, blasonduo is right in that this is a little beyond what you need for the course

Hi, thank you everyone for you help!! If i may clarify with you Jamon, is the reason for the P/N junction forming in relation to the doping of semiconductors with Group 3 and 5 elements?
Thank you in advance!

[jamonwindeyer]

Hi, thank you everyone for you help!! If i may clarify with you Jamon, is the reason for the P/N junction forming in relation to the doping of semiconductors with Group 3 and 5 elements?
Thank you in advance!

Yep that's it! And the subsequent forming of covalent bonds when you bring the two together in a junction

[key to success]

Hi guys,
If someone can help me with the attached multiple choice, I'll much appreciate it! 
Thanks!

[envisagator]

Hi guys,
If someone can help me with the attached multiple choice, I'll much appreciate it! 
Thanks!

This question has 2 components:

First calculate the weight force of the hanging mass: F=mg, which gives 1.96N

You know that the question refers to satellite in orbit around Earth, so you use F=mv^2 / r . where F is the centripetal force which in this case is the hanging mass which 'pulls' the stopper to the centre. So F= 1.96N (found above)

We know that v = 8.37m/s . therefore, v^2 = approx 70 m/s
m = the mass of the stopper
r= 0.6m (given in Q)

Substituting into centripetal force equation, and rearranging to solve for m we get m= 0.01678 kg, which is approx 17g, therefore B is the answer.

Hope this helps, note how we didnt need to use time, its one of those questions which gives more than you need.

[key to success]

This question has 2 components:

First calculate the weight force of the hanging mass: F=mg, which gives 1.96N

You know that the question refers to satellite in orbit around Earth, so you use F=mv^2 / r . where F is the centripetal force which in this case is the hanging mass which 'pulls' the stopper to the centre. So F= 1.96N (found above)

We know that v = 8.37m/s . therefore, v^2 = approx 70 m/s
m = the mass of the stopper
r= 0.6m (given in Q)

Substituting into centripetal force equation, and rearranging to solve for m we get m= 0.01678 kg, which is approx 17g, therefore B is the answer.

Hope this helps, note how we didnt need to use time, its one of those questions which gives more than you need.

That helps heaps! Thanks mate!