# Heisenberg's uncertainty principle

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1. Jun 1, 2015

### AndrejN96

1. The problem statement, all variables and given/known data
Find the minimum uncertainty of the momentum of a small particle with mass m=1g, which is confined within a region of width a=1cm.

2. Relevant equations
Delta(p)*Delta(x)>=hbar/2

3. The attempt at a solution

Delta(p)*Delta(x)=hbar/2
Delta(p)*10^(-2)=hbar/2
Delta(p)=10^2*hbar/2

This looks pretty straightforward to me, but the given mass in this problem is what confuses me.

2. Jun 2, 2015

### rude man

I think you have it right & putting in the mass is a red herring. Maybe they meant to ask for the minimum uncertainty in the velocity.

3. Jun 2, 2015

### insightful

You might want to scan this:

http://en.wikipedia.org/wiki/Particle_in_a_box

Pull quote:

"The uncertainties in position and momentum ( and ) are defined as being equal to the square root of their respective variances, so that:

This product increases with increasing n, having a minimum value for n=1. The value of this product for n=1 is about equal to 0.568 ..."