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    I need help on Part A) ii)... Answer is 4λ But I don't undestand Why is it 4λ ...Can anyone explain please..

    THank You
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    (Original post by tsrguru)


    I need help on Part A) ii)... Answer is 4λ But I don't undestand Why is it 4λ ...Can anyone explain please..

    THank You
    first the formula for a diffraction grating is given by :
    n\lambda=dsin\theta
    it is said its a second order diffraction grating : so
    2\lambda=dsin\theta
    now to find CE use trignometry
    the small triangle ACE..we know AD=2d
    sin\theta=\frac{CE}{2d}
    can you now use the equations to find CE?
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    (Original post by rbnphlp)
    first the formula for a diffraction grating is given by :
    n\lambda=dsin\theta
    it is said its a second order diffraction grating : so
    2\lambda=dsin\theta
    now to find CE use trignometry
    the small triangle ACE..we know AD=2d
    sin\theta=\frac{CE}{2d}
    can you now use the equations to find CE?
    Not really, no...

    I should had mentioned part a) iii) aswell

    a) iii) use your results to show that for the second order image, 2\lambda=dsin\theta
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    The "first order" diffraction means there is a path difference of lambda (one wavelength) between B and D. The geometry of the triangles means that the distance between C and E must be 2 lambda. The 2nd order diffraction happens when the distance between B and D is 2 wavelengths. By the same geometry the distance between C and E must be 4 wavelengths.
    The reason why the distance must be one wavelength between B and D for 1st order, is that this is the condition for the two adjacent waves to constructively interfere. (A half wavelength difference would mean they destructively interfere.) The interference "fringes" you see in this experiment are areas where the light alternately constructively and destructively interferes to give alternative light and dark lines.
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    (Original post by tsrguru)
    Not really, no...

    I should had mentioned part a) iii) aswell

    a) iii) use your results to show that for the second order image, 2\lambda=dsin\theta
    Im sorry I should have read the question properly..it says state..Since I did contributed wrongly, here is a website which I came across which looks the topic in quite detail (not that stonebridge's explanation is not good just a alternative one)
 
 
 
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