A-Level Physics Coursework - Help!

[3v1l |\/|1NiOn]

It's that time of the year again when coursework rears its ugly head. Except this year, I don't get a set outline to stick to, I have to create my own practical. I struggled to think of what to do that would encompass a physics topic and be relatively easy to gain a nice set of results to plot a graph (which is all physics coursework is about really), but still be complicated enough to get me a good grade.

I settled on doing something with electronics as I am notoriously clumsy and innacurate when it comes to metre rulers and other analogue measuring devices. I narrowed my final choice down to coaxial cable, and the idea that I have is this:

To get a length of coaxial cable (30m seems to be the longest I can get for free) and see how the length affects the attenuation of an electrical signal. I'll hopefully do this by finding 30m of space and clamping the cable straight (looping coaxial cable is baad) and then fire a signal down it (the higher frequency I can produce with the school's crappy signal generators the better I think - higher frequencies yield greater attenuation). I will then use a laptop to read the wave at the start and the end, and apparently the program one of my teachers has can subtract one wave from the other - leaving me with the magnitude of signal lost. I'll then cut it down gradually so I can see how length is affected by it.

Someone here must have knowledge on coaxial cable, or has done A-Level physics and can tell me whether or not this will work and/or is enough to get an A or B.

I appreciate any comments, and the sooner the better... It kinda has to be planned out by next week...

[voiceofcod]

I study physics at Oxford uni. Got an A at A-level. However, I don't know a thing about your syllabus, which is what really matters.

What is the purpose? Is it a data analysis project for which the theory is essentially minimal? i.e. is the whole point to get a large set of data and do error analysis?

Or, are you performing an experiment to test a theory of your choosing?

Tell me what they are looking for and I'll see if I can help.

It sounds lame (and it was) but I did 'rotational dynamics' for my coursework and got 43/44 for it (I dropped a mark because my use of diagrams was only 'good', not 'excellent' apparently).

Basically, I gave a run down of the theory of conservation of angular momentum and the derivations of the important equations. I then got a cylinder, drilled holes running from one end to the other, and inserted metal rods at various radii and showed how distributing the same mass differently across the radius affected how quickly the cylinder rolled down a slope (used a digital camcorder and some tipex for the measurements). Plenty to talk about, easy to do, lots of theory, good marks. But this may not be suitable for your syllabus.

[3v1l |\/|1NiOn]

They wanted me to come up with my own experiment (this was the best I could come up with). It's not technically my own theory, more just a 'see what happens and why it happens when i do x.' For example one person in the class is doing how metals affect capacitance, another is doing something to do with ballistic equations and another is doing something about forces affecting Scalectrix.

From what I can tell from my AS stuff, it is a firm balance between theory and data analysis. They want me to know roughly what I'm talking about and the physics reasoning behind it, but they also want me to plot a graph and analyse the causes of errors and comment on the trend line in order to predict what would happen if i had, for example, a 100m cable.

The syllabus is the salters horners one, if that didn't help.

[voiceofcod]

It sounds like your experiment is fine for the purpose. I take it you would do two experiments - one how length impacts on signal attenuation, and another how frequency impacts on it.

The only problem is just how complex the theory needs to be. You'll need more than just saying 'energy is lost due to resitance' - it's actually very complicated how coaxial cable works (such as the capacitance and inductance of it, they come from an oscillating EM field which you won't know anything about). I don't think you can really start talking about Maxwell's equations, which is where all the equations you would use come from.

I think it would be very difficult to actually get an explanation of the physics that was of a high enough level and yet not of a university level. Honestly, I wouldn't actually recommend this project.

If your heart is set on it, you really have to understand the 'transmission line'. Google it, and if you don't get it, I would abandon ship and choose something else.

[3v1l |\/|1NiOn]

As long as you think the experiment will actually work then I'll muddle along with it. I'm fairly sure I can source some good info on coax cable, my step-dad having been an electrical enginner or sorts, and I'm confident my physics teacher will actually have the knowledge to explain some of this complicated theory to me. I may have misinterpreted the extent at which they require theory. Looking over the marking grid theory doesn't really seem to be playing that big of a part in this one as it did in last year's. As long as I can understand what I'm seeing in my results and I can explain it, thats all I need.

I think I'll only test length, but test frequency on the full 30m cable as a preliminary test to see what attenuates most and least and explain that specific frequencies are used for TV in order to maintain a high signal quality.

Thanks for the help.

[voiceofcod]

Good luck with it.

But seriously, I shit you not, coax cable is very complicated if you actually want to derive an equation of what's happening and use it to predict results, rather than just drawing a bit more of a curve on a graph.

Look up 'skin effect' too, it's very important in any cable manufacture. There is a good reason we aren't using really fat wires to reduce resistance other than just the cost.