HSC Physics Question Thread

[jakesilove]

Another Question: not sure how to approach this one. I tried using Keplars' Law but it didn't get me anywhere because I don't know the mass of the star.
Sorry, but you're probably about to get a bunch of questions from me that I should probably find easy! I hope you don't mind too much as I am very grateful Thanks Again!

Hey! I'll just give you a hint, because I'm sure you can get this one out. Keplar's law, equation the ratio of radius and period to the mass of the central object, implies something interesting. For any two objects orbiting the same central star, the value of r^3/T^2 will be a constant. It doesn't actually matter what the mass of the star is, because



So, we can sub in the information known about Alif, to get information out about Ba!

If you can't get an answer, let me know, and I'll post up a solution

Jake

[RuiAce]

Another Question: not sure how to approach this one. I tried using Keplars' Law but it didn't get me anywhere because I don't know the mass of the star.
Sorry, but you're probably about to get a bunch of questions from me that I should probably find easy! I hope you don't mind too much as I am very grateful Thanks Again!

Lol damn Jake beats me in physics

[GeekModeEngaged]

Okay, next up:

[jakesilove]

Okay, next up:

This you just need to know. P-type semi-conductors have an 'acceptor level' close to the valence band. Thus, this is a P-type semi conductor, and must be doped with a group 3 metal.

Note: N-type semi-conductors have a 'donor level' close to the conduction band.

[GeekModeEngaged]

a P-type semi conductor must be doped with a group 3 metal.

Note: N-type semi-conductors have a 'donor level' close to the conduction band.

Sorry, could you please explain what a "group 3 metal" is. I don't do chemistry and I don't recall my teacher explaining it.
Thanks

[RuiAce]

Sorry, could you please explain what a "group 3 metal" is. I don't do chemistry and I don't recall my teacher explaining it.
Thanks

Look for III A and V A. (III and V are Roman numerals for 3 and 5.)

(In fact, ignore everything with B in it.)

https://www.google.com.au/search?q=periodic+table&espv=2&biw=1745&bih=885&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjbsLfOpM3PAhWFjZQKHZRvCF4Q_AUIBigB#imgrc=ARVfilyMkimROM%3A

If your teacher didn't explain this then he/she forgot something quite important in the physics course...

[GeekModeEngaged]

If your teacher didn't explain this then he/she forgot something quite important in the physics course...

It would not surprise me if he forgot something. Am I supposed to use IIIA for p-type and VA for n-type?

[RuiAce]

If your teacher didn't explain this then he/she forgot something quite important in the physics course...


It would not surprise me if he forgot something. Am I supposed to use IIIA for p-type and VA for n-type?

Yes.

Also: Note that boron belongs in group 3 (just call it that, don't have to call it IIIA in the HSC). And note that phosphorus belongs in group 5. These are the standard elements used for doping.

[GeekModeEngaged]

I know this should be relatively simple, but when I tried to use F = BILsin(x), I got F=0.3 N (where l=0.4sin(45), I = 3A and B=0.5T) I'm sure I'll just be missing something simple (either that, or i"m doing it completely wrong), but could you help anyway please

[jakesilove]

I know this should be relatively simple, but when I tried to use F = BILsin(x), I got F=0.3 N (where l=0.4sin(45), I = 3A and B=0.5T) I'm sure I'll just be missing something simple (either that, or i"m doing it completely wrong), but could you help anyway please

Looks like you got the length wrong!

[GeekModeEngaged]

Looks like you got the length wrong!

Oh my god that is so embarrasing. I think it's time to stop trying to do maths for the night 

[katnisschung]

GPE
figure 5.2 shows how the Ep of an object changes with distance either side from planet X.
such a graph is called a gravitational potential energy well or, more simply a gravity
well.
a) add to it a gravity well for a planet which is much more massive.
b) account fro the shape of the graph you have drawn
 
the new graph would have a well with more depth because the mass would mean
more GPE  according to the absolute GPE formula

but wouldn't it also be skinnier and its curve approach zero GPE more quickly
because of its larger mass?

[jakesilove]

GPE
figure 5.2 shows how the Ep of an object changes with distance either side from planet X.
such a graph is called a gravitational potential energy well or, more simply a gravity
well.
a) add to it a gravity well for a planet which is much more massive.
b) account fro the shape of the graph you have drawn
 
the new graph would have a well with more depth because the mass would mean
more GPE  according to the absolute GPE formula

but wouldn't it also be skinnier and its curve approach zero GPE more quickly
because of its larger mass?

I think you're right there! It wouldn't matter as much as your first point, because the 'skinniness' of a gravity well is less obvious upon comparison than the depth of the well. Worth mentioning, I think, but your first point should get you the marks.

[jamonwindeyer]

GPE
figure 5.2 shows how the Ep of an object changes with distance either side from planet X.
such a graph is called a gravitational potential energy well or, more simply a gravity
well.
a) add to it a gravity well for a planet which is much more massive.
b) account fro the shape of the graph you have drawn
 
the new graph would have a well with more depth because the mass would mean
more GPE  according to the absolute GPE formula

but wouldn't it also be skinnier and its curve approach zero GPE more quickly
because of its larger mass?

Hey! So if we have our function of GPE with respect to distance as:



That's really just a graph of the form \(y=\frac{k}{x}\). By increasing the mass of our planet, we are just increasing our value of \(k\). Let's say we take something 10 times greater, so \(10k\). Then compare the graphs (the green graph is the larger planet):



So based on that, I'd actually say that the well is wider! I don't like this question though, because it doesn't specify that the mass is larger specifically, it just says "more massive." Also, I'm not sure whether you are drawing gravity wells that don't tend to negative infinity in the middle, that would alter this slightly and definitely result in a deeper well as you've described

Welcome to the forums Katniss!

[jakesilove]

Hey! So if we have our function of GPE with respect to distance as:



That's really just a graph of the form \(y=\frac{k}{x}\). By increasing the mass of our planet, we are just increasing our value of \(k\). Let's say we take something 10 times greater, so \(10k\). Then compare the graphs (the green graph is the larger planet):

(Image removed from quote.)

So based on that, I'd actually say that the well is wider! I don't like this question though, because it doesn't specify that the mass is larger specifically, it just says "more massive." Also, I'm not sure whether you are drawing gravity wells that don't tend to negative infinity in the middle, that would alter this slightly and definitely result in a deeper well as you've described

Welcome to the forums Katniss!

I sort of assumed this was part of an option that I didn't do, where you do proper three-dimensional-like gravity wells? Maybe Astrophysics? In any case, none of us did that topic, and I was definitely sort of making stuff up.