HSC Physics Question Thread

[RuiAce]

How do you do this question

The radius of earth's orbit is 1.49 times 10^11m and that if Jupiter is 7.783 times 10^11. What is the period in seconds of Jupiter's orbit around the sun?
(note: the period of earth around the sun is 365.25 days) (2 marks)

Thanks

[jamonwindeyer]

Hiya! I'm just wondering if  anyone know whether we need to know Bohrs derivation of the Rydberg constant (for quanta to quarks)? Thank you!

^^^
Just bringing this back to people's attention in case someone who did Quanta happens to know the answer to this one

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And conic, what Rui used up there was an example of Kepler's Law of Periods. It's taught in the HSC course, just so you know it isn't a Prelim question

[jakesilove]

^^^
Just bringing this back to people's attention in case someone who did Quanta happens to know the answer to this one

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And conic, what Rui used up there was an example of Kepler's Law of Periods. It's taught in the HSC course, just so you know it isn't a Prelim question

In response to the Bohr derivation; I can say with fair certainty that you don't!

[Spencerr]

Hiya! I'm just wondering if  anyone know whether we need to know Bohrs derivation of the Rydberg constant (for quanta to quarks)? Thank you!

Hey there,
You don't need to know the exact derivation, I've tried memorising it a few times but it's not worth it haha, but you just need to know a few points about the derivation.
-Bohr used a mixture of classical mechanics and quantum mechanics (i.e. he used classical formulas for kinetic energy and gravitational potential energy) and combined them with quantum mechanics (like his quantisation condition L = nh/2 (pi) ). This was a limitation of Bohr's model as the mixture of classical and quantum mechanics is a problem in itself
- Bohr's derivation of the Balmer's equation and the Rhydberg constant (which were both previously empirically based on the hydrogen spectra) validated his atomic model. Essentially, he won over alot of support from the scientific community.

But for the direct derivation it's not needed, make sure you're well acquainted with how to use the formula to find wavelengths though!
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[amina_98]

i know this may sound very silly, but does anyone have tips on answering multiple choice? im always loosing atleast 10-12 marks in that section. 

[RuiAce]

i know this may sound very silly, but does anyone have tips on answering multiple choice? im always loosing atleast 10-12 marks in that section. 

Well is there any particular reason that multiple choice seems to be a weakness?

Multiple choice is attacked through either calculations (alike short response), process of elimination or immediate deduction. The third option is just something that comes with practice.

If it's a calculation, then the worst thing they can do is throw you a twist. Figure out what the twist is. Not simple? You have to do even more past papers. You only learn tricks by being exposed to them (unless you're that capable).

Otherwise, process of elimination is one of the most common things in multiple choice. Eliminate what is wrong so that you narrow down your opinions. Whilst occasionally this narrows you all the way down to one correct answer, generally you only have two to choose which you just use your brain power to figure out which is right.

Multiple choice is generally more applied (calculations) or logical (reasoning). Practice more of these questions to get better at the style. Board of Studies Multiple Choice can be used if you wish. Also, keep in mind textbooks such as Excel Success One explain the answers to multiple choice as well.

[imtrying]

Hey just a question on the semiconductors topic: I get that n-type semiconductors become better conductors due to the extra electron available for conduction (due to the extra one from the Group 5 impurity added) but how does having more positive 'holes' make p-types better conductors?

[jakesilove]

Hey just a question on the semiconductors topic: I get that n-type semiconductors become better conductors due to the extra electron available for conduction (due to the extra one from the Group 5 impurity added) but how does having more positive 'holes' make p-types better conductors?

Basically, because there are more 'holes' (ie. spaces with a LESS negative charge) it is easier for electrons to move into those regions, as they are repelled less. The hole moves along, and each adjacent electron can move into the space with more ease. Therefore, the semiconductor will conduct more easily, simply because electrons can move in one direction without being impeded as much! Does that make sense? It's a bit of a conceptual leap, definitely a tough topic to understand. I hope my explanation made sense!

[RuiAce]

The way I understood was that holes are technically an absence of an electron where there should be one. That's why they're supposedly +'ve.

When electrons go from the valence band to the conduction band, they move along and then fill a hole ahead of them. But the thing is, because the electron left the original atom it just left a hole behind. So the hole basically moved in the opposite direction of the electron.

Since holes carry a +'ve charge, you're basically causing a lot of positive charge to go in the opposite direction of electrons. Hence conducting electricity.

[imtrying]

Basically, because there are more 'holes' (ie. spaces with a LESS negative charge) it is easier for electrons to move into those regions, as they are repelled less. The hole moves along, and each adjacent electron can move into the space with more ease. Therefore, the semiconductor will conduct more easily, simply because electrons can move in one direction without being impeded as much! Does that make sense? It's a bit of a conceptual leap, definitely a tough topic to understand. I hope my explanation made sense!

Thank you, your explanation does makes sense! This topic is so hard to get my head around, I probably be spamming this thread until my exam haha

[jakesilove]

Thank you, your explanation does makes sense! This topic is so hard to get my head around, I probably be spamming this thread until my exam haha

Then I look forward to plenty more great questions Good luck with your study!

[jamonwindeyer]

i know this may sound very silly, but does anyone have tips on answering multiple choice? im always loosing atleast 10-12 marks in that section. 

I agree with Rui, unless you are super confident; answer all MC questions by eliminating 3 incorrect answers, not picking 1 correct one. This doesn't quite work for calculations, but for others, process of elimination is a great strategy

[imtrying]

Hi would someone be able to explain the answers to these multiple choice questions to me?
With the one with the car speedometer, I assumed eddy currents would oppose the motion of the magnet and go in the opposite direction, but the answer was actually C.
With the other question, I honestly just have no idea

[jamonwindeyer]

Hi would someone be able to explain the answers to these multiple choice questions to me?
With the one with the car speedometer, I assumed eddy currents would oppose the motion of the magnet and go in the opposite direction, but the answer was actually C.
With the other question, I honestly just have no idea

Hey! I can't seem to open the attachments, just me guys or?

[imtrying]

Ive checked and think theres something wrong with my attachments:( Hopefully they work now?