Physics Aftermath

Limerick Dude

madnirvana wrote:

1 watt is 1 joul per second.

and 60 seconds they asked for..so * by 60.

wait what was the question again, because i think i actually did that

JC 2K3

Oh yeah, Q12 (b), how do you get the sound intensity if they don't give you the area of the speaker??

madnirvana

JC 2K3 wrote:

eV = (1/2)mv^2

v = sqrt(2eV/m)

v = sqrt(2(1.6022*10^-19)(700*10^3)/(1.6726*10^-27))
v = 11580473.99 m/s

Correct you are madnirvana

yayee

thank u for your hard work.. i know writing maths in this forum is extremely painful:)

Limerick Dude

JC 2K3 wrote:

Oh yeah, Q12 (b), how do you get the sound intensity if they don't give you the area of the speaker??

welll they said yer man was 3m away from speaker, so i multiplied the power by 3 metres....

microbiek

JC 2K3 wrote:

Oh yeah, Q12 (b), how do you get the sound intensity if they don't give you the area of the speaker??

W/m^2 so 25/9 = 2.777778

ron-burgandy

That Q2 isn't in our book, but it was in an edition of Science Plus (the science version of Exam and Career guide) that I read yesterday. €25 well spent!

The copper was heated by placing it inside a boiling tube covered in boiling water. Anything along those lines should be alright.

I think they will have to mark some of these questions easy...

JC 2K3

madnirvana wrote:

yayee

thank u for your hard work.. i know writing maths in this forum is extremely painful:)

No problem, to be honest I have no problem writing maths in text form, I guess I've just gotten used to it

Limerick Dude wrote:

welll they said yer man was 3m away from speaker, so i multiplied the power by 3 metres....

Yeah... that's wrong.... sure the unit you'd get there would be W m, not W m^-2, so....

Limerick Dude

ron-burgandy wrote:

That Q2 isn't in our book, but it was in an edition of Science Plus (the science version of Exam and Career guide) that I read yesterday. €25 well spent!

The copper was heated by placing it inside a boiling tube covered in boiling water. Anything along those lines should be alright.

I think they will have to mark some of these questions easy...

hmm i think i guessed that

JC 2K3

microbiek wrote:

W/m^2 so 25/9 = 2.777778

I thought of that, but it doesn't make sense. Surely you need the area of the loudspeaker....

Limerick Dude

ugh, the more i read this, the more i realise i got loads wrong! aaaah

ZorbaTehZ

JC 2K3 wrote:

I got confused there, because the charge is supposed to be on the outside of the dome and the gave the diameter....

I took d = 0.07....

It's in my book, but I managed to leave it at school.

This non-trivial result shows that a uniform spherical distribution of charge acts as a point charge when observed from the outside of the charge distribution; this is in fact a verification of Coulomb's law.

http://en.wikipedia.org/wiki/Gaussian_surface

JC 2K3

Ah I see, perhaps I won't be counting that question then...

(Although, since a Van de Graff generator has a rod through the bottom of it where the belts go, it's not a uniform sphere, is it?)

madgal

Carsinian Thau wrote:

I wouldn't worry too much about it. They'll have to adjust the marking scheme to generate a specific percentage of A's B's and C's so you could do alright. Also, you have other subjects to rely on so one paper can't throw you off just like that.

No. I need 2 B2's and 3C2s.

My plans where to get B's in Chemistry and music and C's in french, physics and english.

I just screwed up physics,so now I need to get an A in Chemistry to make up.


Why did Xrays not come up? Just a 7 marker question in Q5. I was raging. I had that all learnt off and was hoping that may give me a few decent marks.
Whoever wrote that paper should be sacked, shot and hung out to dry.

Btw answer to semiconductor Q - Why is silicon a semiconductor ... I said because it is between a good conductor and a good insulator... please tell me I was right.

ZorbaTehZ

JC 2K3 wrote:

Ah I see, perhaps I won't be counting that question then...

(Although, since a Van de Graff generator has a rod through the bottom of it where the belts go, it's not a uniform sphere, is it?)

Do you realize how difficult the math would be if we had to take that into consideration?

Nehpets

Anyone else think physics should be two papers? They could do it like theory and maths or by sections

JC 2K3

ZorbaTehZ wrote:

Do you realize how difficult the math would be if we had to take that into consideration?

madgal

Nehpets wrote:

Anyone else think physics should be two papers? They could do it like theory and maths or by sections

No... perhaps a foundation paper for stupid stupid people like myself who can't even do an honours paper.

madgal

madgal wrote:

No... perhaps a foundation paper for stupid stupid people like myself who can't even do an honours paper.

Would be a bit silly imo having a foundation paper for a non-compulsary subject.

/Aside: It's mad how I can't remember most of what was on the Physics course.

Tomlowe

the principle on which the definition of the ampere is based anyone? is it that a current carrying conductor in a magnetic field experiences a force proportional to the current? i sure hope so

nedward

Current-carrying conductors exert a force on each other is what I said...your answer looks right anyway...

adam_ccfc

When'll the SEC be uploading the mofo?

Smegball

I regret not doing ordinary level now, definite fail

Nehpets

Tomlowe wrote:

the principle on which the definition of the ampere is based anyone? is it that a current carrying conductor in a magnetic field experiences a force proportional to the current? i sure hope so

Principle on which the definition of the ampere is that constant current which when maintained between two straight parallel lines of infinite length and neligible cross section area, placed in a vacuum one metre apart produces a force of 2x10^-7 newtons per metre of length

Bad english there, too lazy to word it exactly

adam_ccfc

Nehpets wrote:

Principle on which the definition of the ampere is that constant current which when maintained between two straight parallel lines of infinite length and neligible cross section area, placed in a vacuum one metre apart produces a force of 2x10^-7 newtons per metre of length

Bad english there, too lazy to word it exactly

But that's the actual definition itself!

Carsinian Thau

madgal wrote:

Btw answer to semiconductor Q - Why is silicon a semiconductor ... I said because it is between a good conductor and a good insulator... please tell me I was right.

That's what I said and I think I read that this morning so let's just assume we're both right.

genericgoon

XD thats is word for word alright

JC 2K3

That's the definition of the ampere, they wanted you to give the general principle of what it was based on, ie. that current carrying conductors produce a magnetic field that produces a force.

Nehpets

balls..

The writing time that took! haha

genericgoon

lol good thing i dont do physics. /me kisses his phys/chem paper.

adam_ccfc

JC 2K3 wrote:

That's the definition of the ampere, they wanted you to give the general principle of what it was based on, ie. that current carrying conductors produce a magnetic field that produces a force.

Yeah, that's what I said, and we're right.:D


They didn't want the definition of the ampere. If they did, they'd just have asked for it!

Carsinian Thau

madgal wrote:

No. I need 2 B2's and 3C2s.

My plans where to get B's in Chemistry and music and C's in french, physics and english.

I just screwed up physics,so now I need to get an A in Chemistry to make up.

Considering everyone else found it so hard, the marking scheme will definitely be changed to accomodate that so you could still get the C.
Alternatively the points for your course could drop or you may surprise yourself in music or even french.

Arctic_Monkeh

Yeah i heard it was a very tough paper this year. Also, did it follow a similar format of previous years?

Carsinian Thau

Arctic_Monkeh wrote:

Also, did it follow a similar format of previous years?

Only with respect to layout.

ApeXaviour

Anyone able to scan in the paper by any chance? I'd like to have a look.

JC 2K3

ApeXaviour wrote:

Anyone able to scan in the paper by any chance? I'd like to have a look.

It'll be on www.examinations.ie by tomorrow, if not a couple of hours.

Feddd

Energy lost by copper in Q2: Anyone else get 924.5J? And for the part after that I completly blanked and didn't know wether or not you had to take into account the heat gained by the copper calorimeter so did it out twice leaving it out in one of them. Will I still get full marks?

I got the same answers as you Zor for Q6.

madgal

Carsinian Thau wrote:

Considering everyone else found it so hard, the marking scheme will definitely be changed to accomodate that so you could still get the C.
Alternatively the points for your course could drop or you may surprise yourself in music or even french.

Its not a points course. I'm moving to Northern Ireland - so the grades are given out ... and you either get it or move on.

Turnip2000

the best thing for anyone to do now is Let It Go. Its over!

Now its time to fret about the coming tests which will be without a doubt worse than that!

Au reviour Physics!!:)

Roonels

section A the focal length experiment, i manipulated the formula in order to get a straight line graph, 1/f=1/u+1/v to become f=uv/u=v with the 'uv' being on the y-axis and the 'u+v' on the x axis...hoping that the y axis over the x axis would equal something which looked right:rolleyes: i was completely going out on a limb with this one....but stuck with it and i a straight line graph resulted, i then took two readings and the both equalled, roughly 12, so i added them together and divided by 2 to get the focal length...any1 else do this? also what was the answer for the filament bulb question in 5? i said because a load of energy is lost as heat? any1 know the story on that freaking star by the way??

madgal

http://img485.imageshack.us/img485/567/physicsts7.jpg

That was my graph lol!! It didnt look right, but at that stage I was in despair and couldn't give a damn.

adam_ccfc

Just an aside here; anyone else off to get disgustingly drunk?

Feddd

ron-burgandy wrote:

The copper was heated by placing it inside a boiling tube covered in boiling water. Anything along those lines should be alright.

But how is the temp recorded then?

What I said was basically like that expt where you add heat to a copper calo to find its SHC. Put it in insulation, drop of oil in each hole, coil in one hole thermometer in the other. That way it is heated and you can also record its temp so it has to be right, right?

madgal

No. Got chemistry and Music still to go.

Plus drink damages brain cells, and after this mornings paper I realise I don't have enough to lose.

genericgoon

Adam sign me up. LC over means drinking start. Its been so long since ive tasted the sweet sweet tast of alcohol(with the exception of grad nite but i was hammered within the hour and cant reallly remember it.)

Limerick Dude

adam_ccfc wrote:

Just an aside here; anyone else off to get disgustingly drunk?

I want to but i dont want to ruin the chances of fcukin up economics on wednesday, wednesday night for sure!!!

spudington16

madgal wrote:

http://img485.imageshack.us/img485/567/physicsts7.jpg

That was my graph lol!! It didnt look right, but at that stage I was in despair and couldn't give a damn.

Hope your really graph intercepted the two axes to get your 1/f value...

Nehpets

spudington16 wrote:

Hope your really graph intercepted the two axes to get your 1/f value...

bollocks.. i should stop reading this!

genericgoon

Avert thine eyes. Youre still looking arent you. AWAY NAO!

Feddd

Energy lost by copper in Q2: Anyone else get 924.5J? The only thing I'm not really sure about atm.

ZorbaTehZ

Feddd wrote:

Energy lost by copper in Q2: Anyone else get 924.5J? And for the part after that I completly blanked and didn't know wether or not you had to take into account the heat gained by the copper calorimeter so did it out twice leaving it out in one of them. Will I still get full marks?

I got the same answers as you Zor for Q6.

At the moment, I just fail to understand why everybody had a problem with Q2. Is it the case that you all only looked at the electrical method to do this experiment? There are countless examples in the book on how this is done tbh ...

Energy lost by the copper piece = Energy gained by the water + Energy gained by the copper calorimeter

mcΔθ = (0.0302).(390).(78.5) = 924.573 J

Therefore:

924.573 = m(w)c(w)Δθ(w) + m(cc)c(cc)Δθ(cc)
924.573 = (0.0455)c(4.5) + (0.0557).(390).(4.5)
924.573 = 0.20475(c) + 97.7535
826.8195 = 0.20475(c)
4038.19 J/Kg.K = c(w)

Minimise heat losses, very common question: ensure room temperature is not very high, use insulation, closed container etc.
Larger mass of copper means larger rise in temperature of the water, which means more accurate result.