Uncertainty principle

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Homework Statement


A mosquito of mass .15mg is found to be flying at a speed of 50 cm/s within an uncertainly of .5 mm/s.

a) How precisely can it's position be known?


Homework Equations



Delta p * Delta x = h bar / 2
p = mv

The Attempt at a Solution



I look at problem originally and simply solved for momentum using the given velocity 50 cm/s. Then i plugged that into the delta x * delta p = h bar / 2.
I got the answer 7.033 X 10^-31

Then I realized that I never used the variable describing the uncertainly of the fly's velocity. Clearly this is relevant to the solution of the problem. I think that I calculated the acutal momentum, as opposed to the uncertaintly of momentum, which the above equation calls for. How am I supposed to differentiate between the actual velocity and the uncertaintly of velocity?

Does the problem want me to give a range of positions? I could solve for the uncertainly of momentum using 50 cm/s + or - .5 mm/s. Could I then could find a max and a min position using the uncertainly equation? What exactly should I be solving for?

Thank you in advance!
 

Answers and Replies

  • #2
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I look at problem originally and simply solved for momentum using the given velocity 50 cm/s. Then i plugged that into the delta x * delta p = h bar / 2.
You found momentum p, which is not what the equation uses. It uses delta p.

Given that [itex]p=mv[/itex] , then [itex]\Delta p=m\Delta v[/itex].

The problem just wants to know delta x.
 
Last edited:

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