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Homework Help: Heisenberg Uncertainty, Need Some Clarification. TIME SESITIVE, HELP

  1. Apr 16, 2010 #1
    Heisenberg Uncertainty, Need Some Clarification. TIME SESITIVE, HELP!!

    1. The problem statement, all variables and given/known data
    Use the Heisenberg uncertainty principle to calculate Deltax for a ball (mass = 100 g, diameter = 6.65 cm) with Deltav = 0.645 m/s.


    2. Relevant equations

    PX = h/(4*3.14)

    3. The attempt at a solution

    So, I took the equation and converted the values with my
    numbers:((h/4π)/(.1kg * .645 m/s))/(.0665m) and yielded an
    answer. The answer I got with these numbers is 1.23 *
    10^-32 m. This answer is wrong and I am not sure why. I only have two hours left to answer this question. I would really appreciate it if someone could guide me on what my mistake is?
     
  2. jcsd
  3. Apr 16, 2010 #2

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    Re: Heisenberg Uncertainty, Need Some Clarification. TIME SESITIVE, HELP!!

    Hello asl3589,

    Why did you divide by the diameter of the ball? :confused:

    [Edit: Also, you seem to be using the more formal [tex] \sigma _x \sigma _p \geq \frac{\hbar}{2} [/tex] where [tex] \hbar = \frac{h}{2 \pi} [/tex]. But keep in mind that relationship is not an equality. If you want an approximate value with a [tex] \approx [/tex] sign and using [tex] \Delta x [/tex] and [tex] \Delta p [/tex], there is a slightly different version of the relation.]
     
    Last edited: Apr 16, 2010
  4. Apr 16, 2010 #3
    Re: Heisenberg Uncertainty, Need Some Clarification. TIME SESITIVE, HELP!!

    Thanks for looking at it. I just assumed that the diameter factors into somehow. Is that unneccesary. If I take that step out the answer is just 8.174 * 10^-34 m. Is that right?
     
  5. Apr 16, 2010 #4

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    Re: Heisenberg Uncertainty, Need Some Clarification. TIME SESITIVE, HELP!!

    That would give you the minimum possible uncertainty in position. But that's not necessarily the approximate uncertainty. The minimum possible uncertainty in position might be the answer your instructor is looking for, but I'm uncertain about that.
     
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