# OCR paper question

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#1
Hi there,

This question is about superposition of electromagnetic waves.

Could someone please explain how to go about question 8)c)iii). of this paper: http://www.ocr.org.uk/Images/131308-...nd-photons.pdf

I know its only a 1 marker, so should be easy but I cant quite understand how in the mark scheme they just 'know' that lambda/4 is equal to 7.5mm.

I understand that the incident microwave superimposes with the reflecting wave to give maxima and minima, but without a distance between the transmitter and reflecting sheet I cant work out a path difference in order to find their phase difference.
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3 years ago
#2
You are forming a standing wave. The question talks about the distance between a maximum (an antinode) and a minimum (node) being 7.5mm. You should know that from drawing a standing wave the distance between a node and an antinode is 1/4 of a wavelength.
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#3
You are forming a standing wave. The question talks about the distance between a maximum (an antinode) and a minimum (node) being 7.5mm. You should know that from drawing a standing wave the distance between a node and an antinode is 1/4 of a wavelength.
So in the case of a standing wave, the nodes represent a minimum intensity, not a trough of the wave?
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3 years ago
#4
(Original post by Sir_Malc)
So in the case of a standing wave, the nodes represent a minimum intensity, not a trough of the wave?
Yes. I think you need to revise standing waves.
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#5
Yes. I think you need to revise standing waves.
So in the case of non-standing, electromagnetic waves, like in the Young's double slit experiment, when we see the light fringes on the detector screen, are the brightest areas either where two peaks or two troughs meet (even though the two troughs have a negative amplitude), and the areas with no light are where a peak meets a trough?
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