HSC Physics Question Thread

[JemexR]

When drawing the bands of conductors, should we draw the conduction band sitting right on top of the valence band or the two bands overlapping? Or is either fine? Also do we say there is no band gap?

Thanks

I would say either as long as you specify that there is no energy gap.

Quick question due to mental blank: What is the term for the minimum amount of energy required for an electron to be released under the photoelectric effect? Thanks!

[Cindy2k16]

I would say either as long as you specify that there is no energy gap.

Quick question due to mental blank: What is the term for the minimum amount of energy required for an electron to be released under the photoelectric effect? Thanks!

Thanks!
Do u mean the work function?

[Cindy2k16]

Hi in 2006 Physics q29 (option) b) i) it says "describe the criteria you would use to determine the reliability of a data source for this purpose"- 3 marks . If reliability is if the information is consistent across many reputable sources, how do you talk about it for 3 marks worth?

[MysteryMarker]

Hey guys, i'm not too sure how to go about this question.

I keep getting a negative cos curve for the current time graph. Because at its current time it has 0 magnetic flux and hence as it rotates in the direction given it will become max flux and vice versa representing a sin curve. Hence to find the current we just find the negative derivative?
Yea, i'm pretty confused with how to go about this question, pre sure answer is B. Appreciate any help given

Cheers.

http://prnt.sc/d0bgpg

[Cindy2k16]

Hey Cindy!

Hysteresis loss is simply the loss of magnetic flux during the transmission process from primary coil to secondary coil. It's not really because of the constant reversal of magnetic polarity, but because the inability of iron core to PERFECTLY transmit the magnetic flux. In other words, you can reverse your magnetic polarity however you like, as long as you have an ideal perfect transmitter of magnetic flux, hysteresis losses cannot occur. Iron core is the best thing we have now and even that isnt perfectly ideal, so hysteresis losses would always occur. And because the equation vp/vs = np/ns relies on the perfect transmission of magnetic flux, energy would be lost because the equation is no longer viable since some magnetic flux is lost.

Best Regards
Happy Physics Land

Hi! Thanks for the answer. I'm still a bit confused through since I've heard somewhere (but ive forgotten) that hysteresis losses are from flux leakage but when I look it up on google I get a lot about reversing the magnetisation of the transformer core? They sound like pretty different things so I'm confused as to what the right one is. Are they both called hysteresis losses?

[jakesilove]

Hey! Could I please have a hand with Q20c   answer a) 20ms^-1 and b)14ms^-1

Hey! Just in future, it'd be super helpful if you post the answers to the first few parts.

So, what do we know about the second part of the motion? Well, actually, we know basically nothing. The ball bounces inelastically, which should mean that neither the horizontal nor vertical components of motion stay the same. So, the first two parts actually won't make a difference to our answer!

Based on the diagram, it looks like the height of motion is at h, when the ball passes through the hole.

Okay, now I'm lost. I actually don't know how to answer this using HSC physics, I feel like there isn't enough information. This is definitely NOT something you can be assessed on in your HSC, so don't stress, but if anyone wants to jump in feel free to answer part c) for me!

[jakesilove]

Thanks!
Do u mean the work function?

Yep! All of the above answers are correct

[jakesilove]

Hi in 2006 Physics q29 (option) b) i) it says "describe the criteria you would use to determine the reliability of a data source for this purpose"- 3 marks . If reliability is if the information is consistent across many reputable sources, how do you talk about it for 3 marks worth?

Hey! It wants 'criteria' for reliability, so there are probably a few things you can talk about. I don't know what the experiment was on, but the obvious thing to discuss is repeating it a billion times. Then, you could take lots of samples etc. to get a more reliable idea of the results as a whole. Finally, you can draw graphs and take averages to increase reliability. You could also compare to others' results! That's three marks, easily

[JemexR]

Hey! Just in future, it'd be super helpful if you post the answers to the first few parts.

So, what do we know about the second part of the motion? Well, actually, we know basically nothing. The ball bounces inelastically, which should mean that neither the horizontal nor vertical components of motion stay the same. So, the first two parts actually won't make a difference to our answer!

Based on the diagram, it looks like the height of motion is at h, when the ball passes through the hole.

Okay, now I'm lost. I actually don't know how to answer this using HSC physics, I feel like there isn't enough information. This is definitely NOT something you can be assessed on in your HSC, so don't stress, but if anyone wants to jump in feel free to answer part c) for me!

If it was elastic, could you then infer that V2 = the velocity of the ball when it comes into contact with the ground, and the angles to the normal would be identical?

[jakesilove]

If it was elastic, could you then infer that V2 = the velocity of the ball when it comes into contact with the ground, and the angles to the normal would be identical?

Yep absolutely, but the questions specifically says it's inelastic, right?

[jakesilove]

Hi! Thanks for the answer. I'm still a bit confused through since I've heard somewhere (but ive forgotten) that hysteresis losses are from flux leakage but when I look it up on google I get a lot about reversing the magnetisation of the transformer core? They sound like pretty different things so I'm confused as to what the right one is. Are they both called hysteresis losses?

If you're a bit confused, then that's good, because hysteresis is super confusing. Don't worry about understanding it at this point, just be able to talk about it for a sentence (ie hysteresis causes energy loss etc.) and move on with your life. There are heaps of things you actually DO need to learn, and this isn't one of them! It's just the icing on the cake

[Cindy2k16]

Hey! It wants 'criteria' for reliability, so there are probably a few things you can talk about. I don't know what the experiment was on, but the obvious thing to discuss is repeating it a billion times. Then, you could take lots of samples etc. to get a more reliable idea of the results as a whole. Finally, you can draw graphs and take averages to increase reliability. You could also compare to others' results! That's three marks, easily

Oh sorry I forgot to give more context but It's not about an experiment :/

"During your study of Medical physics you identified data sources, and gathered, processed and presented information to explian why MRI scans can be used to detect abnormalities in the body. Describe the criteria etc"

To answer the question I dont think u need to know about med physics but rather talk about assessing the reliability of secondary sources. But as far as I know that involves comparing information from reputable sources to ensure the info is consistent. But for 3 marks just saying that hardly seems enough. The past papers book I have has a sample answer talking about author credibility, making sure its verified by a scientific institution etc but isnt that validity/accuracy rather than reliability? The book also has some mistakes in it so I'm not sure how much to trust it.
TIA

[FallonXay]

Hi! For Question 9, the answers say C - how is this true, because shouldn't there still be eddy currents generated in R but just broken - so R will still experience some resistance though just not as much as Q (I've probably asked about this before earlier in the year but I forgot  )

Regarding Q8, how can you tell whether the source of power is AC/DC - this one said that it was DC (is there a different symbol used to show AC power sources?)

And lastly, I don't understand the answers for Q15; shouldn't electrons/ holes move in opposite directions? - The Answer is C.

Thanks in advance~ 

[Cindy2k16]

Hi! For Question 9, the answers say C - how is this true, because shouldn't there still be eddy currents generated in R but just broken - so R will still experience some resistance though just not as much as Q (I've probably asked about this before earlier in the year but I forgot  )

Regarding Q8, how can you tell whether the source of power is AC/DC - this one said that it was DC (is there a different symbol used to show AC power sources?)

And lastly, I don't understand the answers for Q15; shouldn't electrons/ holes move in opposite directions? - The Answer is C.

Thanks in advance~ 

Hi for your last question- the electrons and holes move in opposite directions in an electric field- not necessarily in a magnetic field though (though they can). If you use your right hand palm rule for the conventional current (movement of positive charge) youll find there is a downwards force on the 'holes'. Now electron flow is in the OPPOSITE direction to conventional current. So when you use your left hand palm rule (or whatever youve been taught to use for the flow of a negative charge) you point ur thumb in the OPPOSITE direction to the conventional current and youll find that the electrons ALSO experience a downwards force.
Thus both holes and electrons move to the bottom of the rod ie. the same side of the rod.
Therefore C. hope this helps

[Yasminpotts1105]

Silly question, but when using a vector diagram to show the net resultant force should you put in lengths of each side or angles or not??