** LC Physics 2017

Arrigle

Any tips folks? Thinking NEWTON'S Second Law for the expt question

thetalker

I was thinking that as well, maybe for electricity they'll ask the thermistor question since that hasn't come up in awhile.
I also imagine g by pendelum will pop up.

ciara18

Anyone doing physics, is it too risky to briefly skim over mechanics definitions and leave out the bulk of the chapters? If I look at everything else?

thetalker

Why would you skim over mechanics when it's probably the second largest chapter.
Mechanics and Electricity are probably enough to get through the entire exam when you consider how many optional q there are.

A97

I think Mechanics typically comes up as:

1 experiment
A few parts of Q5
A long question (usually Q6)
A half question (Q12)
Sometimes parts of other topics where relevant (bits and bobs in nuclear physics, particle physics and magnetism)

I would recommend at least a working knowledge of Mechanics but time is short now. If you know everything else really well, you should be fine. You can do the other three experiments, you could probably still do a good job of Q5 given the fact you don't have to answer them all. Q6 is a no go, but 7, 8, 9, 10, 11 and 12 should be okay. 12 is fine since you have choice like in Q5, and the others will have either no Mechanics or not very much in them.

The concern about leaving things off is that the other questions could be hard, but you are better off doing the rest of the topics to a high standard rather than speaking yourself thin on all of them.

So in short, know everything except Mechanics really well. If you have time, do the Mechanics experiments and then cover the basics. I can't guarantee anything, but you could probably make it work.

But note that if you end up doing anything STEM related in college, make sure your Mechanics is up to scratch since it can be very useful.

ciara18

thetalker wrote: »

Why would you skim over mechanics when it's probably the second largest chapter.
Mechanics and Electricity are probably enough to get through the entire exam when you consider how many optional q there are.

I'll learn the definitions and experiments I just want to avoid answering the other places it comes up as it's often very poorly answered!

Mr Rhode Island Red

ciara18 wrote: »

Anyone doing physics, is it too risky to briefly skim over mechanics definitions and leave out the bulk of the chapters? If I look at everything else?

I'm doing that but with electricity. Our teacher told us that most of the time you can get away with just knowing one out of mechanics or electricity really well, and just having a rough idea of the definitions in the other.

Having said that I know this lad who did his leaving last year, and I think he got a B2 without having a clue of mechanics or electricity at all, but he knew his light, heat, magnetism, sound and particle physics perfectly well.

Liordi

I'm learning everything except magnets and electricity. I've looked through other papers and it seems like it's still possible to get 100% doing that.

carefulnowted

Would I be okay not knowing light, do ye think? I know electricity, mechanics, optics, heat, sound, magnetism and modern physics fairly well. Our teacher didn't cover the light chapter with us, but I have notes on it if needed.

Liordi

Yeah, I'm pretty sure you can leave out 2 topics completely and still be fine once you know the experiments.

jogd1234

Tbh I've not really learned light, electricity or magnetism well. Hoping mechanics, heat, optics, particle physics, nuclear physics & the electron will be enough. Should be I think.

thetalker

Whats in the light chapter? It seems unfamiliar, is it like the photoelectric effect or is it optics like snells law?

jogd1234

thetalker wrote: »

Whats in the light chapter? It seems unfamiliar, is it like the photoelectric effect or is it optics like snells law?

All the characteristics of light (polarisation, diffraction etc), Doppler effect, dispersion, different types of light, how to get wavelength of light (which I wouldn't know if it hit me on the head).

thetalker

jogd1234 wrote: »

All the characteristics of light (polarisation, diffraction etc), Doppler effect, dispersion, different types of light, how to get wavelength of light (which I wouldn't know if it hit me on the head).

Ah well the diffraction grating Q came up the last two years so doubt it'll pop up again.
wavelength is just c=f(wavelength)
And f is just E=hf
You're sorted if you know those two usually.

carefulnowted

I feel like I know nothing for this exam hopefully it's just last minute jitters

thetalker

You must have faith in the power of the force ted, all four fundamental forces. :P

randylonghorn

The exams must be nearly over, people are starting to talk out of their fundament ...:pac:

covfefe98

Mechanic and Electricity defo (you'll be sorted with these two) come up every year and have all the manditory and demonstration experiments learned (anything from those can come).

carefulnowted

Don't know what to make of that The experiments were nice enough but Section B was a bit iffy for me...I had to do the resistance question which turned out a bit messy for me.

Mr Rhode Island Red

Got 20 metres per second squared for g in question 1, so I knew I had made a hames of it, ended up having to do the electricity experiment as an extra question to cover myself.

Q5 and 6 weren't too bad. Didn't really know how to draw a spectroscope or whatever for Q9, Q10 Xray question was ok and so was 12.

Overall trickier than what I thought it would be.

thetalker

I imagine a lot of people either forget to divide by 40 for the period in the pendulum or square it when graphing.
I got 9.84 by slightly adjusting my graph after getting 10

Section Below was trickier, started the spectroscope question before realising I had no idea how to draw one. So I went and did the polarization​ q instead.

How did people get the bungee jump periodic and the sum of moments question?
I was unsure how to do those tbh.

carefulnowted

What were the particles used in satellite signals (Q11)? I threw down positive/negative ions because I hadn't a notion.

thetalker

Wouldn't it be photons?
Since the satellites use microwaves

carefulnowted

Oh...I said photons for the particles transmitted in optical fibres

thetalker

Maybe it's photons for.both?
I didn't do that question tbh.

Mr Rhode Island Red

thetalker wrote: »

I imagine a lot of people either forget to divide by 40 for the period in the pendulum or square it when graphing.
I got 9.84 by slightly adjusting my graph after getting 10

Section Below was trickier, started the spectroscope question before realising I had no idea how to draw one. So I went and did the polarization​ q instead.

How did people get the bungee jump periodic and the sum of moments question?
I was unsure how to do those tbh.

For the periodic time I pulled some formula out of the tables...2pi/omega I think, ended up with around 3 seconds, but I'm not sure if I'm right.

thetalker

I got around 11 sec which is probs wrong
I made the acceleration 9.8 and used the a=wsquared/s where s was the displacement.
But it feels off, I just didn't have time to check over the reasoning for alot of stuff.

jogd1234

Anyone know how to get which is the most accurate value for t in the pendulum experiment? I just used T = 2 pi x square root of l/g and used g = 9.8. Then got which value of t is closest to the actual tension. Not sure if that's how they wanted you to do it

ciara18

jogd1234 wrote: »

Anyone know how to get which is the most accurate value for t in the pendulum experiment? I just used T = 2 pi x square root of l/g and used g = 9.8. Then got which value of t is closest to the actual tension. Not sure if that's how they wanted you to do it

I could be totally wrong but I just said the last value because it had the longest length of string, and the longer the length of string the smaller the percentage error

carefulnowted

ciara18 wrote: »

I could be totally wrong but I just said the last value because it had the longest length of string, and the longer the length of string the smaller the percentage error

I had that but then put a line through it and said the shortest length of string, as it would be least affected by air resistance/draughts.

Mr Rhode Island Red

In Q10, Did anybody else get something to the power of 25 for the number of electrons crossing the photocell in a minute?

I said 2 microamps divided by the charge on the electron would give the number of electrons per second, and then multiplied that by 60 to get electrons per minute.

Does anyone know if that's right?

thetalker

I converted to amps first and multiplied by 60 before dividing by the electron charge.

so my calculation was (2*10^-6)(60)

---

(1,6*10^-19)

which gives; 7.5*10^14 electrons

Mr Rhode Island Red

And, same question, to get the velocity of the electron did you take the energy of the Xray photon and set it equal to the kinetic energy of the electron?

ciara18

Mr Rhode Island Red wrote: »

And, same question, to get the velocity of the electron did you take the energy of the Xray photon and set it equal to the kinetic energy of the electron?

Yeah I did that anyway!

Liordi

I thought that the experiments questions were really nice. I liked 5 and 12 too. Thought the ending of 6 was a bit awkward and I wasn't really sure of the colours at 7, hoping for a H2 but I'm not sure.

roisiny

ciara18 wrote: »

I could be totally wrong but I just said the last value because it had the longest length of string, and the longer the length of string the smaller the percentage error

I did the opposite to this. Crossed out shortest and said longest. I'd say both could end up right as in that experiment you can have too long a string but also too short a string ?

A97

The measurement with the longest time has the smallest percentage error. The error in the measurement would be roughly similar each time, maybe about a second or so, so the longest time is the most accurate.