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    Had this in a exam and wanted to know the correct answer

    A beam of plane light waves, initiall travelling in air with amplitude A1 strikes the upper surface of a horizontal sheet of glass, with air both sides. At each interface, 25% of the energy is reflected, the rest is transmitted. Let A2 be the final amplitube of the part of the original beam which enters the upper surface of the glass, reflects from the lower surface, then passes back into air through the upper surface. Find the ratio of final and initial amplitude A2/A1 assuming that there is no spreading of the wavefronts.
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    I think its  0.75^2 \times 0.25 = 0.141 . What did you make it in the exam?
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    Ye your right I worked it out before. But I forgot to do the last interface in the actual exam
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    Nothing worse than realising something like that after the exam... At least you should get some method marks!
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    lol.. indeed. I've been looking at some other questions i've messed . So many questions over all the exams I've ever done have been messed by not reading the question properly and I even missed one question in the physics one just done *face palm*.

    Ye you'r right about the method marks but some part of me says I won't get marks for even the method probably paranoia lol

    Thanks for the help
 
 
 
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