HSC Physics Question Thread

[FallonXay]

Hey there,  since I'm online I'll give you a quick explanation. 

Weight is defined as the force experienced by an object when placed inside a gravitational field. As you know large celestial bodies like the moon and the earth have their own gravitational field that is directed towards the centre of the body. Midway between the earth and the moon, an object will experience both a force of attraction towards the centre of earth from earth's gravity and another force of attraction towards the centre of the moon from the moons gravity however these two forces oppose each other, acting in separate directions.  Hence the gravitational fields cancel out leaving the object near weightlessness (due to the absence of a NET FORCE). The other answer that might seem right is if the object is in orbit but remeber that at that point the object is still being subjected to a weight force or attractive force which forms the centripetal force keeping it in orbit. Feel free to ask any questions if you need me to clear things up

Ps is this a hsc paper? Or a schools paper. I've done this question before..

Thanks for the prompt answer!
Yeah, this was from the 2011 Exam Choice Trial HSC Physics paper.
Just with the question: Wouldn't the strength of the gravitational field exerted by the Earth be stronger than that of the Moon. So at the halfway point, wouldn't the net force experienced still be acceleration due to gravity on Earth?

[Spencerr]

Thanks for the prompt answer!
Yeah, this was from the 2011 Exam Choice Trial HSC Physics paper.
Just with the question: Wouldn't the strength of the gravitational field exerted by the Earth be stronger than that of the Moon. So at the halfway point, wouldn't the net force experienced still be acceleration due to gravity on Earth?

In terms of it simply being a MC question, using the values for the mass of the Earth and the mass of the Moon and Newton's Law of Gravitational Attraction would be too much. I would say it is the most correct answer out of the four.

[FallonXay]

In terms of it simply being a MC question, using the values for the mass of the Earth and the mass of the Moon and Newton's Law of Gravitational Attraction would be too much. I would say it is the most correct answer out of the four.

ok, fair enough. Thanks! 

[Klexos]

This is from the 2014 CSSA and I need help because my answer doesn't agree with the MC, rather it agrees with parts of MC answers

[jamonwindeyer]

(Image removed from quote.)

This is from the 2014 CSSA and I need help because my answer doesn't agree with the MC, rather it agrees with parts of MC answers

Hey Klexos! Subtle trick here, this is a circular magnetic field. That means that you don't need the cos30 in your calculation, the coil is always parallel to the field lines!  if you take that out you should get one of the answers in the options

[Klexos]

Hey Klexos! Subtle trick here, this is a circular magnetic field. That means that you don't need the cos30 in your calculation, the coil is always parallel to the field lines!  if you take that out you should get one of the answers in the options

Oooh as in the radial electromagnets?

I'm so done ;___;

[RuiAce]

Hey Klexos! Subtle trick here, this is a circular magnetic field. That means that you don't need the cos30 in your calculation, the coil is always parallel to the field lines!  if you take that out you should get one of the answers in the options

Ah shit, completely overlooked that one

Oooh as in the radial electromagnets?

I'm so done ;___;

Well they're not "electromagnets" necessarily though

[jamonwindeyer]

Oooh as in the radial electromagnets?

I'm so done ;___;

They might be! The diagram doesn't suggest that though, and it doesn't make a difference for the question, you can have permanent magnets setting up a radial magnetic field

[conic curve]

What other information do I need for GPS right now (for an assignment other than the information I have down here)

1. Satellites send microwaves into the area where the receiver is shown to be
2. When the satellite signals are sent out, the satellite themselves record the exact time and position this occurs and sends this information along
3. Now as the receiver receives the signal, it compares the time at which it receives the signal and the when it was sent out
4. This time frame tells us an approximation to were you can be in terms of regions, because light travels at 3 time 10^8

Is this sufficient enough?

[jamonwindeyer]

What other information do I need for GPS right now (for an assignment other than the information I have down here)

1. Satellites send microwaves into the area where the receiver is shown to be
2. When the satellite signals are sent out, the satellite themselves record the exact time and position this occurs and sends this information along
3. Now as the receiver receives the signal, it compares the time at which it receives the signal and the when it was sent out
4. This time frame tells us an approximation to were you can be in terms of regions, because light travels at 3 time 10^8

Is this sufficient enough?

You've got the rough idea, but remember this happens for 3 or 4 different satellites at once! This allows the GPS receiver to triangulate its exact position on the earth. Note that 3 satellites are required for a precise 2 dimensional position (latitude/longitude), and a fourth is required to accurately determine height you may want to do some research into the specifics of how that works, and further (if you want), into the extra considerations required to account for the effects of special/general relativity (which can throw things off a little)

[Loki98]

Hey guys,
Could someone please explain how an AC induction motor works and what the practical was to demonstrate the principle of an induction motor.
Thanks =]

[jamonwindeyer]

Hey guys,
Could someone please explain how an AC induction motor works and what the practical was to demonstrate the principle of an induction motor.
Thanks =]

Hey Loki! So the practical you did to model this was something like the magnet rotating under the disc!

So, we hang a conducting disc on a string and rotate a magnet beneath it. Due to the changing magnetic field, eddy currents form in the disc. Their direction is determined by Lenz's Law, and so we know that the induced current will generate a new magnetic field that opposes the change that created it. But how do we oppose a rotating magnet?

This is a little tricky to explain, but consider some point marked X on the side of the disc, just above the rotating north pole. The north pole rotates away. That specific point X doesn't want the north pole to leave (oppose the change), and so it wants to pull it back. The net effect of this is that the disc chases the magnet.

So, an AC induction motor. These motors rely on eddy currents to spin the rotor, and it works in the exact same way as above. The stator consists of six or more field coils in pairs, fed a special version of an AC current (it's 3 Phase) which essentially creates a rotating magnetic field. The rotor spins in response to induced eddy currents. The rotor is shaped a bit like one of those hamster wheels that you see the little hamsters running on, which allows eddy currents to flow and maximise the torque provided by the motor (details on that shape not important).

You could go into more detail here, but this covers you for the sorts of questions asked in the HSC does that make sense?

[MysteryMarker]

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.

[jakesilove]

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! I didn't do Quanta, so maybe someone that did can help you out! Otherwise, if you post one question where they DID include the electron, and one where they DIDN'T, I can take a look and try to discern a pattern? I would generally say that, if it specifically tells you the NUCLEUS lost mass, you would ignore electrons. If it said something like the 'element' lost mass, then use the electrons. That being said, totally ignoring electrons shouldn't be an issue; they're freaking small. If you completely convert an electron into energy, you get 8*10^(-14) Joules of energy out; negligable!

[Loki98]

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