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# AQA Physics A - Unit 4 watch

1. Ok I have a more specific question below, but anyone know of any revision notes for this unit 4? Or synoptic?

Righty, question time - i'm a little stuck! June 03 Section B Q1

Allow me to try and explain:

Microwave Transmitter ||--->____|Detector|->_________| Metal Plate

Detector moves up and down to find Maxima and Minima.

'The detector is placed at a position where the intensity is a minimum. When it is moved a distance of 144mm it passes through 9 maxima and reaches the 9th minima from the starting point. Calculate the wavelength of Minima's...'

Now I thought aha! distance between minima = 1 wavelength therefore 144x10^3 / 9, but apparently in this situation there half a wavelength apart. Is this due to reflection/stationary wave etc?? Help!
2. think of it as a wave on a graph (e.g sin graph) where the x axis is the middle and the waves are above and below.

each peak of the graph is a maxima and whenever the graph touches the x axis is a minma.

at least that's how i see it, i may be wrong.
3. This helped me understand that question (doing same syllabus):

That is whats actually happening, as the waves are reflected off the metal screen.

Looking at that animation, ingore what each wave is doing, only look at the sum of the waves (the black wave), the distance between maxima and minima are the same, and are both half a wavelength. The sum of the two waves is also as standing wave, the markscheme gives a mark for this somewhere, i think.
4. http://antonine-education.co.uk/physics_module_4.htm
These notes are great! Also has notes on other aqa modules
5. Yeah the antonine-education.. notes are very useful, and stick right to the syllabus. Good luck for tomorrow! (I sure as hell am going to need some luck..)
6. (Original post by CharXlotte)
Yeah the antonine-education.. notes are very useful, and stick right to the syllabus. Good luck for tomorrow! (I sure as hell am going to need some luck..)
Well they are mostly in line with the syllabus, but some parts seem to go into too much detail and it lacks some basic definitions but much better than anything else (at least for medical physics!)

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