## Uncertainty

$\Delta p \Delta x\geq \frac{h}{4\pi }$

Chem_Mod
Posts: 18913
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 737 times

### Uncertainty

Find the uncertainty in the position of a marble of mass 1.5g given that it's speed is known to 0.55m/s

Chem_Mod
Posts: 18913
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 737 times

### Re: Uncertainty

I'll break down the calculation. After rearranging the Heisenberg equation to find the uncertainty in position, we have: delta-x= [(6.626e-34Kg*m^2/s)/(4*pi*1.5e-3kg*0.55m/s] The units should cancel out to give an answer of 6.4e-32m.

Claire Miller 3C
Posts: 8
Joined: Fri Jul 15, 2016 3:00 am

### Re: Uncertainty

In the new workbooks, the answer is different. In the key it says the uncertainty in position is 3.2x10^-32 m. But with the calculations you gave the answer is different. But the question is still the same. What is the right answer?

Khachik_Hmayakyan_2E
Posts: 25
Joined: Sat Jul 09, 2016 3:00 am

### Re: Uncertainty

I'm having the exact same problem. I went through the calculation multiple times and consistently end up with 6.4 instead of 3.2. Which is exactly double what the answer should be. I'm confused why the workbook is giving an answer that's half the value I calculated.

Luke_Lucido_3B
Posts: 15
Joined: Wed Sep 21, 2016 2:58 pm

### Re: Uncertainty

Im having the exact same problem can anyone help?

Ronica_Patel_3G
Posts: 10
Joined: Sat Jul 09, 2016 3:00 am

### Re: Uncertainty

Don't you have to double the speed since it is +/- ? Instead of doing the division with 0.55, I used 1.1 and got 3.2 * 10^-32 as the answer.

Ashley Curtis 2O
Posts: 21
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Uncertainty

So if the equation does not use a +/-, then the uncertainty of speed is the value given, but if it does include a +/-, the uncertainty is the value doubled? I thought that the value always meant that it the uncertainty was that value above or below? For example, even if the question had not said +/- 0.55 m/s, I thought that the speed was doubled anyways because it was assumed the uncertainty was .55 of the actual speed in either direction.

Brenton Hwee 2J
Posts: 15
Joined: Wed Sep 21, 2016 3:00 pm

### Re: Uncertainty

Can we use the Heisenberg Uncertainty Principle for all atoms or does it only apply to certain elements?

Alexandria_Leaf_2F
Posts: 30
Joined: Fri Jul 15, 2016 3:00 am

### Heisenberg post module assessment #2

The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. I am not really sure where to begin with this question.

Chem_Mod
Posts: 18913
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 737 times

### Re: Uncertainty

Answers to all the above questions. :-)

The question states: "within ± 0.55 m.s-1 "

Therefore delta v = 1.1 m.s-1

And the final answer is delta x = 3.2 x 10-32 m

As I discussed in class the Heisenberg Uncertainty Principle applies to everything but it is only observed at the small scale (e-, protons, etc).

The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius. If it known to within 1% of the H radius then calculate 1% of 0.05 nm, and use the answer for delta x (uncertainty in position).

Zsanielle Moncayo 1E
Posts: 13
Joined: Wed Nov 18, 2015 3:00 am
Been upvoted: 1 time

### Re: Uncertainty

How was 1.1 found for delta v? I am lost on that and how would we proceed if the speed is given along with +_ of a certain amount. For example, a speed of 5+_0.3 m.s^-1. What would we use as delta v to find delta p?

Chem_Mod
Posts: 18913
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 737 times

### Re: Uncertainty

Zsanielle Moncayo 1E wrote:How was 1.1 found for delta v? I am lost on that and how would we proceed if the speed is given along with +_ of a certain amount. For example, a speed of 5 +/- 0.3 m.s^-1. What would we use as delta v to find delta p?

As I discussed in class, the value would be 4.7 to 5.3 m.s-1. Therefore the total spread or uncertainty is 0.6 m.s-1.