HSC Physics Question Thread

[jamonwindeyer]

Thx for the help Jamon,
Also, what would be a suitable description and diagram to explain how a solar cell works and its applications?

You're welcome! So the diagram can be very simple, a quick something like this would suffice! Label the elements of the PN junction, show an external circuit, and give some indication of the release of an electron and it's subsequent movement.



In terms of a description, you wouldn't want more than a few sentences, I'd do something like:

- Sentence One: Identify the PN junction and the setup of the depletion zone
- Sentence Two: Describe the photoelectric effect releasing an electron
- Sentence Three: Identify that the electron moves through the external circuit due to the electric field set up by the depletion zone

No more detail than that for a describe question, then just delve in a bit more for explain let me know if you need any of these points clarified

[Spencerr]

Quanta to Quarks Question:

For Mass defect calculation questions, when do you include the mass of the electrons? Different examples include the mass of the electrons or just use the mass of the constituents of the nucleus.

Cheers.

Hey there I've encountered questions where I have both included and not included the mass of the electrons. However, in most of the questions i DID NOT include the mass of the electrons. This is because during a nuclear reaction (as is the case of an alpha decay or a beta decay), it is NUCLEUS undergoing fission (or fusion). The nucleus breaking apart into daughter nuclei is what produces the mass defect and the electrons do not play a part in this. Furthermore, mass defect is linked with binding energy (using Einstein's mass energy equivalence E = mc squared). Binding energy holds the nucleons together in the nucleus and also does not deal with electrons. So in most cases, I would not include the mass of the electron

[Phillorsm]

Hey guys, I need some help understanding Eddy currents. In particular, how to determine the direction of the Eddy current in terms of the physics principals involved when moving a sheet of metal through a changing magnetic field.

[jamonwindeyer]

Hey guys, I need some help understanding Eddy currents. In particular, how to determine the direction of the Eddy current in terms of the physics principals involved when moving a sheet of metal through a changing magnetic field.

Hey Phillorsm! I'd be happy to help here, the rule I recommend is the right hand grip rule! That said, it's best to show you with an example, do you have an example of one of the questions you are struggling with?

[Phillorsm]

Yep, sure. This one still makes no sense haha

[jamonwindeyer]

Yep, sure. This one still makes no sense haha

Okay cool! So we know that the eddy currents are only being produced at A and C, because those are the only locations where the magnetic field is changing. Let me know if you need help with that bit, otherwise, let's focus on direction

First, let's look at Point A. We are introducing a magnetic field going out of the page. Thus, Lenz's Law says we will want to create a magnetic field going into the page that counteracts it. How do we create such a field?

Pretend that the metal plate is a solenoid, and we can use the right hand grip rule. The right hand grip rule is as follows. Hold your right hand out in a thumbs up position. In that position, if your thumb is pointing in the direction of the North pole you want to create with a solenoid, then your fingers wrap in the direction the current should flow. Although this is a rule used mostly for solenoids, it also works here!

At Point A, we want a field going INTO the page. Thus, we need to set the plate up so that the field lines are going INTO it on the side closest to us. This means, the side closest to us needs to be set up as a south pole. This means the other side of the plate is a north pole, that is, your thumb points into the page with the right hand grip rule.

If you use your right hand grip rule with your thumb pointing into the page, you'll find your fingers wrap clockwise. Thus, the eddy currents also wrap clockwise.

The exact same analysis works in reverse at Point C, where we are removing some of the field out of the page. Lenz's Law says we want to introduce a new field out of the page to counteract that change. Thus, our same analysis applies with everything reversed, and you'll get eddy currents flowing anti-clockwise

Read this over a few times, it's a tad confusing, but this is how you determine the direction of eddy current flow. Now, in the questions, you wouldn't go into depth about the right hand grip rule, you would just explain that the eddy currents need to oppose the change that created them. Less field out of the page? We need to introduce more field out of the page to compensate for that. By right hand grip rule, this requires an anti-clockwise eddy current flow

Does that make sense at all?

[Phillorsm]

Yes it certainly does make sense! Thanks so much Jamon!! That was a massive help, physics trial on Monday, and I feel much better about eddy currents now 
I'll get back to you if I need help with any other concepts 

[conic curve]

When it says "describe GPS" (5 marks) what should I write?

Please do not involve any scientific principles into this and the wave properties associated with as that is another dotpoint

[Happy Physics Land]

When it says "describe GPS" (5 marks) what should I write?

Please do not involve any scientific principles into this and the wave properties associated with as that is another dotpoint

This is a bit absurd to describe GPS without referring to scientific principles.
But if you do have to refer to scientific principles please refer to wave transmission and explain what triangulation/trilateration is

I will give you a few dotpoints to consider:
- GPS = Global Positioning System
- GPS is a constellation of 24 low-earth orbit satellites
- Each GPS satellite weighs 1 tonne with about 5 metres span
- GPS works based upon the relay of radio waves between satellites
- GPS uses the principle of triangulation (latitude, longitude, altitude), and the time difference between when the one satellite receives the signal from a transmitting antenna and when the receiver antenna receives the same signal from the satellite in order to accurately spot the location of the destination
- GPS works in any weather conditions since all satellites are in the external universe
- GPS satellites make 2 orbits around the Earth in less than 24 hours
- GPS softwares are often seen on cars and mobile phones
- Google Maps is a similar form of GPS

[conic curve]

This is a bit absurd to describe GPS without referring to scientific principles.
But if you do have to refer to scientific principles please refer to wave transmission and explain what triangulation/trilateration is

I will give you a few dotpoints to consider:
- GPS = Global Positioning System
- GPS is a constellation of 24 low-earth orbit satellites
- Each GPS satellite weighs 1 tonne with about 5 metres span
- GPS works based upon the relay of radio waves between satellites
- GPS uses the principle of triangulation (latitude, longitude, altitude), and the time difference between when the one satellite receives the signal from a transmitting antenna and when the receiver antenna receives the same signal from the satellite in order to accurately spot the location of the destination
- GPS works in any weather conditions since all satellites are in the external universe
- GPS satellites make 2 orbits around the Earth in less than 24 hours
- GPS softwares are often seen on cars and mobile phones
- Google Maps is a similar form of GPS

Yeah I will be referring to the scientific principles as well but that's another thing I need to do for a presentation

I need hints for the following questions I have attached

[RuiAce]

Yeah I will be referring to the scientific principles as well but that's another thing I need to do for a presentation

I need hints for the following questions I have attached

All formula work.

For some questions, figure out what is constant (e.g. in F=mg, g and F will vary on different planets but the mass of the object is still unchanged) and carry through.

When doing calculations, always figure out what you actually KNOW, before selecting a formula to try out.

[conic curve]

All formula work.

For some questions, figure out what is constant (e.g. in F=mg, g and F will vary on different planets but the mass of the object is still unchanged) and carry through.

When doing calculations, always figure out what you actually KNOW, before selecting a formula to try out.

wait what do you mean, I'm still confused

Care to elaborate further?

[RuiAce]

wait what do you mean, I'm still confused

Care to elaborate further?

I mean exactly that. Use your formulas as appropriate.

And as for what's in my brackets, the acceleration on each planet is different but the mass of the object is not.

[bethjomay]

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!

[conic curve]

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