HSC Physics Question Thread

[blasonduo]

Hey,

This is a 2013 HSC multiple choice question. You see I recognise it as one of faraday's first motors but I don't understand how to determine the direction of rotation. Would appreciate some help.

(Image removed from quote.)

Hello! This is more applying your knowledge of the Motor Effect.

For this, we have to use our good ol' right hand!

We know the current is going down the page (thumb)
We know its a north pole and the magnetic field lines are going away from the magnet (fingers)

We then can see where our palm is facing, (which is into the page!) but as we move backwards our direction of magnetic field changes VERY slightly! (as we see in the diagram) It is this slight chance which causes the wire to rotate CLOCKWISE around the magnet

[gawdn]

Hello! This is more applying your knowledge of the Motor Effect.

For this, we have to use our good ol' right hand!

We know the current is going down the page (thumb)
We know its a north pole and the magnetic field lines are going away from the magnet (fingers)

We then can see where our palm is facing, (which is into the page!) but as we move backwards our direction of magnetic field changes VERY slightly! (as we see in the diagram) It is this slight chance which causes the wire to rotate CLOCKWISE around the magnet

Ah! I’m a bit daft turns out I had the right hand rule and everything but I got the direction a clock goes wrong. Whoops Thank you - seems I always figure out these things after I post them for the world to see.

[jamonwindeyer]

help please... like i know the information but i dont know how to direct it to answering the question properly, could someone give me an example and explanation on how to approach this?

I think you might have forgotten the attachment?

[julies]

Hey!
I don't understand how to distinguish the theory of general relativity from special relativity... :/
thanks in advance

[jamonwindeyer]

Hey!
I don't understand how to distinguish the theory of general relativity from special relativity... :/
thanks in advance

- Relativity, the idea in general, is the idea that we have to make measurements with respect to a frame of reference. That is, we can only measure velocity of one thing with respect to another
- Special relativity was Einstein's theory on how this worked for objects moving at relativistic speeds (time dilation, length contraction, etc)
- There is also Einstein's Theory of General Relativity, but that is beyond the syllabus

[winstondarmawan]

Hey there,

They would experience an attractive force - not sure what the second mark is for :/

Yes, my question is more when will the SNF balance with the electromagnetic? I think that's where the second mark is allocated and it sucks that this paper doesn't have solutions.

[ProfLayton2000]

HSC 2001 q26: "In the context of semiconductors, explain the concept of electrons and holes" , 8 marks

What other things do I have to mention other than:
Definition of semiconductor
Doping to get n/p type
N has electron as main charge carrier
P has hole (area of positive charge) as main charge carrier
The movement of these carriers allows for improved conductivity in the semiconductor

BOSTES marking criteria was reallllllllllll helpful.

[blasonduo]

HSC 2001 q26: "In the context of semiconductors, explain the concept of electrons and holes" , 8 marks

What other things do I have to mention other than:
Definition of semiconductor
Doping to get n/p type
N has electron as main charge carrier
P has hole (area of positive charge) as main charge carrier
The movement of these carriers allows for improved conductivity in the semiconductor

BOSTES marking criteria was reallllllllllll helpful.

These are some great points!!

Just to add to it, I would add diagrams of the doped semiconductors and how the energy band gap decreases due to this (see diagram attached )

and to add a VERY brief explanation how the knowledge of semi-conductors allowed technologies to benefit society such as solar cells. (but this probably isn't even needed )

Goodluck for your exam!

[Anfar3]

Hey guys,

Can I get a response to the operation of solar cells and how they work for example if it was a 4 marker. i always seem to lose marks with solar cells as I do not really understand it/ cant describe it.

Thanks

[blasonduo]

Hey guys,

Can I get a response to the operation of solar cells and how they work for example if it was a 4 marker. i always seem to lose marks with solar cells as I do not really understand it/ cant describe it.

Thanks

Hey! Let's see what we can do!

Firstly, we have 2 semiconductors, a N-type and a P-type and what we do is we "stick" them together, and this does something very peculiar.

As an N-type semiconductor has extra free electrons, these electrons will want to fall into the holes into the p-type semiconductor. This will cause something we call a Depletion zone

This depletion zone will act as an electric field, This is because electrons have a negative charge and as the electrons moved towards the p-type semiconductor, the P-type side of the depletion zone is now slightly negative, and the N-type side of the depletion zone is slightly positive. Electrons will continue to jump the gap from the N-type to the P-type, making the electric field stronger and stronger until the electrons can no longer jump the gap (As the electric field applies a force to the electrons!)

Now, we attach a circuit to this combined semiconductor and add the power of the sun!! The sun here is just an application of the photoelectric effect, where all it does is pass energy to the electrons, making the electrons able to move but due to the depletion zone, they cannot pass into the P-type, meaning the only way they can move is through the external circuit (which it does!!) Due to this flow of electrons through the circuit, a current is produced!

annnnnnnd voilà! A solar cell!

Just a HUGE reminder! Don't get this mixed up with the photocell!

I hope this helps! If you have any questions about this! Feel free to ask!

[Anfar3]

Legend!

9.4- describe differences between solid state and thermionic devices and discuss why solid state devices replaced thermionic devices

Do we need to know abt the operation of npn junctions and forward/reversed bias for this dotpoint?

Thanks

[blasonduo]

Legend!

9.4- describe differences between solid state and thermionic devices and discuss why solid state devices replaced thermionic devices

Do we need to know abt the operation of npn junctions and forward/reversed bias for this dotpoint?

Thanks

Not really! That is past the course!

All you really need to do is identify the function of solid state devices, (not really the physics behind it) and why they were superior to thermionic devices

[blasonduo]

Also!!! Goodluck everyone!!

Next exam, physics! Study hard and study well, we will get through this together

[sidzeman]

For the BCS theory and superconductors - do superconductors posses 0 resistance AT their critical temperature or BELOW it. Also, the BCS theory only accounts for DC current correct?

[blasonduo]

For the BCS theory and superconductors - do superconductors posses 0 resistance AT their critical temperature or BELOW it. Also, the BCS theory only accounts for DC current correct?

Yes! AT that temperature!! Just remember the graph, the critical temperature is when it hits 0 resistance and falls on the x-axis!

Yep! DC only! (at our level anyway )

You are spot on