HSC Physics Marathon 2013-2015 Archive (5 Viewers)

[Mr_Kap]

re: HSC Physics Marathon Archive

Explain the function of a split ring commutator in a DC generator compared to the function of a Slip Ring in an AC generator. 3 MARKS

 

[astroman]

re: HSC Physics Marathon Archive

Who is doing astro option?

 

[atargainz]

re: HSC Physics Marathon Archive

Explain the function of a split ring commutator in a DC generator compared to the function of a Slip Ring in an AC generator. 3 MARKS

Split ring reverses current every half cycle to maintain the rotation of the motor in the same direction, slip ring rotates with the coil and maintains electrical contact

 

[atargainz]

re: HSC Physics Marathon Archive

Who is doing astro option?

meeeeee just got up to astro in the past paper i'm doing

 

[Mr_Kap]

re: HSC Physics Marathon Archive

Split ring reverses current every half cycle to maintain the rotation of the motor in the same direction, slip ring rotates with the coil and maintains electrical contact

GENERATOR!! i said

 

[atargainz]

re: HSC Physics Marathon Archive

GENERATOR!! i said

my bad, For AC power generation, a generator consists of slip rings which rotate as the armature coil rotates. Since there is contact with the brushes throughout the whole rotation of the armature coil, current is induced in both directions, hence producing an alternating current. For DC power generation, a generator has a split ring commutator which operates similar to that of a motor’s commutator – ensures that current only travels in one direction, hence producing a direct current

 

[Mr_Kap]

re: HSC Physics Marathon Archive

Explain what a change in gravitational potential energy is and why it is a negative. 3 MARKS

 

[astroman]

re: HSC Physics Marathon Archive

meeeeee just got up to astro in the past paper i'm doing

Can u tell me what filters are used for in observing stars? I honestly have no idea.

 

[godofindolence]

re: HSC Physics Marathon Archive

this is actually much more complex than it looks... many people assume 34 m to be the flight's maximum height and do not account for the range in their equations and get 29.8m/s (which is close but not correct). The thing is if you do this, the bird could reach 34 m high but only 10m wide. the answer is 30m/s (may be a decimal there) and uses quite complex simultaneous equations - the answer would be on the 2012 hsc marking guidelines.

I honestly think the answers are wrong

 

[malcolm21]

re: HSC Physics Marathon Archive

I honestly think the answers are wrong

what did you get for the answer? iirc I got 30.1 or 30.2 or something that rounded down to 30

 

[atargainz]

re: HSC Physics Marathon Archive

what did you get for the answer? iirc I got 30.1 or 30.2 or something that rounded down to 30

I got 30.05 when I did it, no complicated simultaneous equations lol

 

[godofindolence]

re: HSC Physics Marathon Archive

Explain what a change in gravitational potential energy is and why it is a negative. 3 MARKS

Gravitational potential energy is a measure of the amount of energy required to bring an object from a point of infinity into a point within a gravitational field. A change is gravitational potential energy therefore measures the work done in order to physically move the object. At a point of infinity, the GPE of an object is obviously 0, and as it approaches the gravitational field, GPE is lost, and instead being converted to KE, thus, it follows that GPE is negative.

 

[Drsoccerball]

re: HSC Physics Marathon Archive

Can u tell me what filters are used for in observing stars? I honestly have no idea.

When observing a star with our eyes the colour green becomes easier to see than other colours as our eyes are more sensitive to green. Furthermore devices such as photographic film are sensitive to the blue colour. Therefore in order to find a compromise and actually discover which one is "actually" brighter we use filters. We do the B-V where B is the blue colour and V is the green in order to develop a colour spectrum. This allows us to understand to what extent a star is blue or green. (The more negative the star is the more blue it is) Furthermore the use of this colour spectrum can allow us to get a "unbias" reading for the apparent magnitude of a star. We can then use this new information in tandem with the HR diagram to find the absolute magnitude more accurately.

 

[godofindolence]

re: HSC Physics Marathon Archive

Can u tell me what filters are used for in observing stars? I honestly have no idea.

Well filters can be used to determine the colour index of the stars. This is done by viewing them through blue and yellow filters. A large main sequence star (O and B class for example) is more blue in colour and therefore have a much lower apparent blue magnitude compared to yellow. This means that its colour index (B-V) is far lower than that of a G and K class stars. This colour index corresponds accurately with the position of a star on the H-R diagrams and allow for easy and quick classification of stars.

Filters can also be used to determine the black body curve using the methods above. Black body curve is obviously really helpful because it allows us to determine temperature and class etc.

 

[atargainz]

re: HSC Physics Marathon Archive

Can u tell me what filters are used for in observing stars? I honestly have no idea.

I assume you're referring to B-V index (same principle applies to all filters). A blue filter allows for only light in the blue part of the spectrum, this is the 'blue magnitude' (B), a visual filter allows only light from the yellow-green portion of the spectrum -- known as the visual magnitude (V). Eg, when a blue star is observed through a blue filter it will appear bright, and conversely will appear dull when seen through a visual filter. Meaning its blue magnitude will be small and visual magnitude will be large (keeping in mind the smaller or more negative the value the brighter it is), the B-V index is essentially the difference between the blue and visual magnitude, meaning that a blue star will have a more negative value (or smaller). Vice versa, a yellow/red/orange star will have a less negative value (or larger). By using the B-V index astronomers can determine the surface temp of stars, since hotter stars a blue and cooler stars are red, it can also determine the spectral class etc. Other filters and indexes can be used, not just B, V.

You should have a read of mrreditor's astro notes he posted in the astro section, they're gun as

(too slow lol)

 

[Crisium]

re: HSC Physics Marathon Archive

1) What does the relativity of simultaneity demonstrate?

2) Explain why the twin's paradox is not essentially a paradox.

 

[Mathsisfun15]

re: HSC Physics Marathon Archive

twins paradox isn't even in the syllabus

 

[Mathsisfun15]

re: HSC Physics Marathon Archive

For the quanta to quarks folk
Theories and experiments not only help increase our understanding but also generate new questions.
Use the standard model of matter to support this statement.
6 marks

 

[Mathsisfun15]

re: HSC Physics Marathon Archive

1) What does the relativity of simultaneity demonstrate?

Events that are simultaneous in one frame of reference are not necessarily simultaneous when viewed from a different frame of reference

 

[Crisium]

re: HSC Physics Marathon Archive

Events that are simultaneous in one frame of reference are not necessarily simultaneous when viewed from a different frame of reference

That's what the relativity of simultaneity is

But what does it demonstrate?