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Homework Help: [Multiple Choice] wavelength of an object. de Broglie wavelength

  1. Apr 30, 2008 #1
    [SOLVED] [Multiple Choice] ...wavelength of an object. de Broglie wavelength


    Which of the following would you expect to have the largest wavelength associated with it?

    (A) a quick-moving bee
    (B) an electron orbiting a nucleus
    (C) a slowly lumbering elephant
    (D) the earth orbiting the sun


    The wavelength of a particle is called the de Broglie wavelength.

    wavelength = [tex]\frac{h}{momentum}[/tex]

    h = Planck's constant


    My thoughts...

    (A) A quick moving bee... its wings are flapping at high frequency. that would mean it has a short wavelength. But I don't think the wings is involved in the question. hehe =)

    (B) electron... smaller than the wavelength of light but is still detectable. In fact, my textbook shows that its wavelength (traveling at 2% of the speed of light) is larger than a ball bearing a mass of 0.02 kg traveling at 330 m/s.

    (C) elephant... my textbook says that "a particle of LARGE MASS and ordinary speed has too small a wavelength to be detected by conventional means."

    (D) earth... well, it's also a large mass. But it does travel at a blazing speed.

    Is the answer (A) Electron???
    'cuz a bee travels much slower than the electron... hmm...
    Please help!!!
    Last edited: Apr 30, 2008
  2. jcsd
  3. Apr 30, 2008 #2
    I would say electron.
    p = mv

    electron max v can be 3E8
    bee min v can be 1

    electron max is .. E-27?
    bee mass is ~ E-3 or 4
  4. Apr 30, 2008 #3


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    Staff Emeritus
    Science Advisor

    Why not try putting some figures in?
  5. Apr 30, 2008 #4
    Good point...

    should I just make estimates? The question doesn't give any figures.
  6. Apr 30, 2008 #5

    Can you translate please? hehehe :confused::smile:
    I don't understand "3E8" ... "E-27"...
    Last edited: Apr 30, 2008
  7. Apr 30, 2008 #6
    Do you think I should? It's just supposed to be a simple problem... 'What would I expect'...

    But since I don't know what to expect.... oh well. Fine, I'll put some figures in. :frown:
  8. Apr 30, 2008 #7
    1E8 = 1*10^8

    don't need exact numbers
    say actual bee mass is 257 g
    you can use 1*10^-3 g or even 1*10^-4 g..

    you should know electron mass (u will be using it a lot in physics ...)
    and you must know that nothing can exceed speed of light: 3e8
  9. Apr 30, 2008 #8
    Ahhh..... okay. E for EXPONENT. duh!!!!

    so it's 10[tex]^{8}[/tex]
  10. Apr 30, 2008 #9


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    Homework Helper

    Well if I was faced with this question I would have to say the electron.


    firstly (even though this is wrong to do) assume all move with the same velocity.
    That would make [itex]\lambda \propto \frac{1}{m}[/itex]

    so the one with the least mass would have the biggest wavelength...the electron has the smallest and hence the largest of them all.
  11. Apr 30, 2008 #10


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    Staff Emeritus
    Science Advisor

    Yea, just pick some numbers; it's better than just guessing! So, for an elephant, say, it has a speed of about 3m/s, mass of 1000kg, thus a momentum of 3000kgm/s. Plug this in your formula. Do the same for the other cases.
  12. May 1, 2008 #11
    Okay... the answer does seem to be (B), Electron orbiting a nucleus.

    Quick moving bee = 2 x 10[tex]^{-31}[/tex] m
    (0.0005 kg, 6.7 m/s)

    Electron = 10[tex]^{-10}[/tex] m

    Elephant = 10[tex]^{-37}[/tex] m
    (3000 kg, 2 m/s)

    Earth = 10[tex]^{-39}[/tex] m
    (6 x 10[tex]^{24}[/tex] kg, 30,000 m/s)

    T H A N K S . G U Y S ! ! !
    i'M nOw dOnE wItH mY PhYsICs..... pretty fun. learned a lot.
  13. Jun 19, 2010 #12
    Re: [SOLVED] [Multiple Choice] ...wavelength of an object. de Broglie wavelength

    we know another formula that
    (as, [tex]\upsilon[/tex]=c/[tex]\lambda[/tex])

    using velocity also you can solve it.
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