AQA physics AS issues and preparation problems

Ok, luckily Physics is a course which you are given a lot of help in the exam for, in regards to formulas and whatnot. You seem adept with Unit 1, but not with unit 2. That is the opposite to me, but each to their own. With unit two, what can be a bit of a bummer is that there is more "tricks" and of the top of the head knowledge to know compared to unit 1. For example, in stationary waves, you will only know be able to find the wavelength if you know that the distance between 2 nodes is 2 lambda. Thats an example of course, but generally, there is more to memorise for Unit 2. FORTUNATELY, the data sheet in unit 2 is your bible. Know it inside out. Finally, just do other past papers. It is not too hard to find on the internet ones from before. Your school will have some from before then. And remember, at the end of the day, Physics is a subject a lot of people take and a lot of people struggle in. You are doing better than you think compared to many. I go to one of the top grammar schools in the country and even still your mock results are better than some of my peers. You are doing fine, just keep going, and realise that the grade boundaries are generally rather low. good luck!

Ok, luckily Physics is a course which you are given a lot of help in the exam for, in regards to formulas and whatnot. You seem adept with Unit 1, but not with unit 2. That is the opposite to me, but each to their own. With unit two, what can be a bit of a bummer is that there is more "tricks" and of the top of the head knowledge to know compared to unit 1. For example, in stationary waves, you will only know be able to find the wavelength if you know that the distance between 2 nodes is 2 lambda. Thats an example of course, but generally, there is more to memorise for Unit 2. FORTUNATELY, the data sheet in unit 2 is your bible. Know it inside out. Finally, just do other past papers. It is not too hard to find on the internet ones from before. Your school will have some from before then. And remember, at the end of the day, Physics is a subject a lot of people take and a lot of people struggle in. You are doing better than you think compared to many. I go to one of the top grammar schools in the country and even still your mock results are better than some of my peers. You are doing fine, just keep going, and realise that the grade boundaries are generally rather low. good luck!

But how is "the distance between 2 nodes is 2 lambda"?

I think he means lamda/2 . If you took a standing wave which just has a node at each end you will notice that you have only one anti node so you have half a wave so hence the distance between the nodes is half a wavelength

Posted from TSR Mobile

I think so too. Thanks for contributing anyway

What topics do you struggle with most in unit 2? And unit 1 for that matter

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What topics do you struggle with most in unit 2? And unit 1 for that matter

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I didn't get any question wrong in mechanics by far.
I think my problem is with the waves-optics bit, and a little bit of the materials.

All of waves or certain parts of it?

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The intensity graphs bit, I'm not sure if the exam actually requires me to draw an intensity graph beside a given one. The marking scheme states that it must be accurate. It's frustrating. The confusion between path and phase difference as well.


Oh, and in mechanics, some 6-mark questions ask you to describe how to carry out a certain experiment. I never answered that correctly.

I have to go quickly I'll be back in 30 mins so post anything else you want help with. For single slit remember that the central fringe is double the width of the other fringes and that for double they are all the same width. I'll answer your other questions when I get back

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The intensity graphs bit, I'm not sure if the exam actually requires me to draw an intensity graph beside a given one. The marking scheme states that it must be accurate. It's frustrating. The confusion between path and phase difference as well.


Oh, and in mechanics, some 6-mark questions ask you to describe how to carry out a certain experiment. I never answered that correctly.

Path and phase difference are related but they are different. Phase difference is a measure of where one part of the wave is in relation to another part of the wave in relation to it's wave cycle, where phase difference =2πd/lamda. Path difference is only used for explaining interference patterns really so I'll use an example to illustrate it. If you used a coherent monochromatic light source and a double slit to diffract them you would observe bright and dark fringes. Why does this happen?

So the first thing to know is that the light source is coherent, so for the sake of this example I'll assume that the phase difference is 0 (as long as its fixed its fine). So if I took a point p on the wave, which let's say starts at 0 amplitude. If the wave was to travel one wavelength, p would move up to its Max then down to its min then back to 0. If the wave travels a multiple of lamda it will still end up in the same place. Since the source is coherent we can assume that p starts in the same place from each slit.

The path difference itself is the difference in distance between the top slit and the bottom slit to that point on the screen. Let's say the distance from the bottom is 1 and the distance from the top is 1+2lamda. The path difference is therefore 2lamda. As explained above, this extra distance effectively has no effect on the position of p so it will arrive perfectly in phase (well technically it is a multiple of 2π out phase but same idea) so you get constructive interference and a bright fringe.

If the path difference was a multiple of (n+0.5)lamda eg 1/2lamba then on one wave p will be at exactly the opposite point as it would be on the other one, so you get destructive interference and a dark fringe



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Wow, that was really helpful. I'm really thankful for your time.
I appreciate it!

No worries. Anything else?

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Any tips for the 6-mark questions both in unit 1 and unit 2?

You mentioned that AQA didnt have many papers available.
I compiled all of the papers for our specification which started in 2009 and put them up here
http://aqa-physics-papers.comlu.com/
For obvious reasons, they are missing the June 2014 papers but you can ask a teacher for these.
Hope this helps.
Check out my site uberyaks.com for any other notes you may need