Past papers!! Need some advice (1 Viewer)

[ragingcurry]

Every time I do past papers and I come across 4/5 mark questions, I get like a brain freeze!! I don't know what to write and always turn to the answers, to see what they have written. How do I prevent this? Does this happen to everyone at the start?

PLS help

 

[leehuan]

Plan your answer. If you don't know what you're writing about, sitting there makes things worse.

Mark allocations are indicative of how much they want to see on the paper.

At this point in time you should also feel safe to actually OPEN THE MARKING CRITERIA (not necessarily the sample answers), look at EXACTLY WHAT THEY WANT, and PROCESS that in your head. Identify what you actually need to write, and then on the side of the paper DO SOME PLANNING.

If you want to go a step further back, do the paper open book and read the textbook as you formulate the answer. But when you're writing it, think about HOW YOU would write it in an exam, instead of copy the textbook.

(Sometimes useful tip: Include relevant mathematical equations)

 

[leehuan]

Specifically the part about does it happen to everyone at the start though -

Yes. In my reading time I tend to freak. But I don't let that overwhelm me as I try to figure out what's what.
Then after I've done the multiple choice, I start to properly enter exam mode. Q21 is usually a cliche type question (possibly projectile motion) so that puts me fully into exam mode quite quickly. Then once I'm in my thinking mode, I can start to figure out the gaps.


Also, the highest mark in my school for the half yearlys was like 76% (band 5 max, no band 6ers). By the HSC (raw HSC mark), it increased up to 87% (steady low band 6)

 

[ragingcurry]

Yo leehuan can you pls explain the Michelson morley experiment to me. I think I get it but sometimes I get confused. The thing I don't get is how are they measuring the speed of the earth relative to the aether? And how does the interference pattern stuff work? Can you pls explain it to me it would be really helpful.

 

[leehuan]

Weak analogy:

Consider myself running on an ordinary race track or even grass. Whenever I am running, I feel air particles bumping into me as if there was wind blowing on me.

If there is motion of one object (in this case, me) relative to another (the atmosphere in this situation), then the motion can be detected through some kind of 'wind'.

So if the Earth is rotating through the aether, then an aether wind is going to be formed as a consequence.

Because the aether is the medium through which light waves propagate through, because there is an aether wind 'altering' the nature of the aether, it must be that the aether wind will change the speed of light.

Therefore MMX happened in an attempt to determine the EXISTENCE of the aether wind. If there was no aether wind, conversely there can't have been an aether. From that, it could be possible to deduce the speed of Earth relative to the aether and everything else (note: aether was believed to be an absolute frame of reference).

 

[leehuan]

Suppose a light wave was travelling in this direction
---> RIGHT

And so was the aether wind
---> RIGHT

Then the light wave will pick up a bit of velocity because they move in the same direction

Suppose the aether wind was now moving ^UP or vDOWN. Then the speed of light will be slowed by some extent

Suppose the aether wind was now moving
<---LEFT
AGAINST the light wave, then the speed of light will probably be slowed more significantly.
_____________________

The apparatus of MMX was a light source, a half-silver mirror, two perfect mirrors and an interferometer. The diagram is neatly set up in physics in focus.

Suppose a light beam was released from the light source. The half-silver mirror aims to split it up into two. One ray goes to mirror 1, and one goes to mirror 2.

Now, here's the thing.

ONLY ONE OF THE TWO RAYS will move ACROSS the aether wind
The other will FIRST MOVE WITH THE AETHER WIND, then secondly AGAINST IT

Again, refer to the diagram.

The two light rays are reflected by the mirror and back to the half-silver mirror. (A half-silver mirror is basically a mirror that has been decomposed by UV light I think... to make half of it become silver. But you don't need to know about the nature of the half-silver mirror. The basic concept is that the mirror reflects it one way, and the silver just allows it to pass through). Once the two light rays come back, they get reflected to the interferometer.

 

[leehuan]

I am multi-posting this one time so that things can be digested more slowly.

Now, because one moves across the aether wind, and the other moved against it, what's gonna happen is that the nature of the two light beams has altered. Because we know that waves superimpose each other through either constructive OR destructive interference (preliminary topic - the world communicates), there will be an interference pattern formed which the interferometer aims to DETECT.

Now, the total length of the apparatus matters. Because equipment might be off by length, this naturally can affect our results. Hence the apparatus is rotated 90 degrees to ignore this problem.

The problem is solved, as we now look for a CHANGE in the interference pattern. IF there is a CHANGE in the interference pattern, the aether wind exists.

But it turns out there wasn't. This is the null result - the experiment was inconclusive. The aether model wasn't exactly disproved, but it still lacked evidence to show that it existed anyway.
____________________

There may be some things explained unclearly. Just comment again and some other physicist will help you out. I'm busy now.

 

[wu345]

You gotta know your stuff thoroughly and know what the question is asking - It might be better when starting off to look at the criteria before you write an answer to a 4+marker (or get a tutor/friend/teacher to get you started, ask them to explain what the question wants and to give you a basic structure of a good answer). Keep practising and you should get the hang of it to be able to do them without looking at the criteria first or getting help

 

[ragingcurry]

Thanks Leeuhan. It's starting to make more sense and hopefully I get it by reading over it again and again if I still have any questions I'll just ask you or someone else.
But thanks anyways

 

[Nailgun]

Lel, I made a post in your other thread (in the Space section)