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The refractive index for an observer

  1. May 28, 2014 #1
    hello

    i have this question
    " a liquid has refractive index (n). find the refractive index of this liquid for an observer if the liquid have a velocity (v) to this observer "

    i have my solution in an attachment
    please look at it and tell me if it is the right solution

    thank you very much
     

    Attached Files:

  2. jcsd
  3. May 28, 2014 #2

    xox

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    The approach is correct up to the point where you make a mistake in the calculation of [itex]v'_x[/itex]. The formula that you use is incorrect, look at the term [itex]1-\frac{v^2}{c^2} v_x[/itex], what you want is [itex]1-\frac{vv_x}{c^2} [/itex]
     
    Last edited: May 28, 2014
  4. May 28, 2014 #3
    sorry but i dont get it.
    can you explain it more. i thought my formula is correct
    or is there something is forget?
    what about the rest of the solution

    please if you have time, can you give me the complete solution to this question
    i have tomorrow an exam and i have no time
    please do me this favor
    thank you very much
     
  5. May 28, 2014 #4

    xox

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    No, it isn't.

    Once you make this error, everything else becomes incorrect. You need to learn how to check your own work, especially after your errors are pointed out to you.

    We do not do your homework for you, you don't learn anything if I do it for you. I gave you the exact error in your derivation, your speed composition formula is wrong and I pointed out your exact error.
     
  6. May 28, 2014 #5

    Orodruin

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    Staff Emeritus
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    To add to what xox has already said. Your end result cannot be correct on dimensional grounds. Dimensional analysis is always a good check to see if your result makes sense. In your case you are subtracting a velocity squared from a velocity in the numerator. Since velocity has dimension length/time, velocity^2 has dimension length^2/time^2 and you cannot add or subtract quantities of different dimensions.
     
  7. May 28, 2014 #6
    omg that is so embarrassing
    sorry but im out of time. thats is the reason for my stupid mistake
    i get it and have again my solution in an attachment


    yes you are soooo right.

    thank you again
     

    Attached Files:

  8. May 28, 2014 #7

    xox

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    It is better but you still have algebraic errors. Check your work.
     
  9. May 28, 2014 #8
    i checked it but didnt find any errors
     
  10. May 28, 2014 #9

    xox

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    Yes, it is right now.
     
  11. May 28, 2014 #10
    Ok. Thank you for your help
     
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