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Please help me,, Mastering physic rounding number

  1. Mar 30, 2009 #1
    please help me,, Mastering physic.. rounding number :(

    A photon of wavelength 4.38×10^−2 nm strikes a free electron and is scattered at an angle of 38.0 degree from its original direction.

    Find the wavelength of the scattered light.
    and my answer is this 4.43×10−2 nm (correct answer)

    Find the change in energy of the photon.

    E= hc / lambda1 = 1.24*10^-6 / (0.0438*10^-9) = 28310.50 eV

    E= hc/ lambda2 = 1.24*10^-6 / (0.0443*10^-9) = 27990.97

    and the change in energy is 319.529..
    i have tried to enter 319 or 320 but mastering physic gave me

    "Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures."

    please help to round this... TT

    ***hate mastering physics...
     
  2. jcsd
  3. Mar 30, 2009 #2

    Redbelly98

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    Re: please help me,, Mastering physic.. rounding number :(

    Since the wavelength was given to 3 significant figures, the energies are each known to 3 significant figures.

    This makes the two energies accurate to the nearest ___ eV.

    Does that help?
     
  4. Mar 30, 2009 #3
    Re: please help me,, Mastering physic.. rounding number :(

    what did you mean by the nearest ____ eV??

    so, what number should i enter?
    320 and 319 don't help much...

    i already lost some points because of it.. :(
     
  5. Mar 31, 2009 #4

    Borek

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    Re: please help me,, Mastering physic.. rounding number :(

    If I understand correctly you have used rounded down 443 to calculate energy here - you should use whatever came out from the calculator. Use full precision when calculating, rounded down values are for reporting only.
     
  6. Mar 31, 2009 #5

    Redbelly98

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    Re: please help me,, Mastering physic.. rounding number :(

    I mean, is it accurate to the nearest 1eV, 10eV, 100eV, or what? Remember, we're using 3 significant figures here.
     
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