
#1
Dec1004, 12:14 AM

P: 138

How do you go about finding the percentage in the uncertainty of momentum, if you already know the momentum and delta momentum? I'm asking because both of them end up being the same; thus I'm wondering if I'm terribly wrong. Any advice?




#2
Dec1004, 06:37 AM

Sci Advisor
HW Helper
P: 3,149

To find the percentage change divide the change in momentum by the (starting) momentum and multiply by 100%. The change in momentum has units of momentum but the percentage change has no units so they are not the same.




#3
Dec1004, 08:42 AM

P: 138

The thing which I've discovered is that when I use that formula, I only end up with 100% back again. Are delta p and p supposed to be the same? For I've taken the things I know, the uncertainty in position and charge, and rearranged them in order to solve for things which I don't know.




#4
Dec1004, 12:30 PM

P: 138

Percentage of Uncertainty
Any ideas guys?




#5
Dec1004, 12:31 PM

Sci Advisor
HW Helper
P: 2,538





#6
Dec1004, 02:13 PM

P: 138

It is about Heisenberg's Uncertainty Principle. We are given the uncertainty for the position of the 1 KeV electron, and we're asked to find the percentage of uncertainty in it's momentum. Now, I've already found the uncertainty of momentum. However, when I use that answer and solve for momentum, both mometum and the uncertainty in momentum are equal. Thus when I use the % formula: (delta p *100%)/p, I end up with 100% as my percentage. What am I doing wrong?




#7
Dec1004, 02:39 PM

Sci Advisor
HW Helper
P: 2,538





#8
Dec1004, 02:41 PM

P: 138

Doesn't that mean that my percentage in my uncertainty is 100%?




#9
Dec1004, 03:07 PM

Sci Advisor
HW Helper
P: 11,863

Daniel. 



#10
Dec1004, 03:10 PM

P: 138

the uncertainty of position is .100 nm




#11
Dec1004, 03:28 PM

Sci Advisor
HW Helper
P: 11,863

Daniel. 



#12
Dec1004, 03:36 PM

P: 138

The formula for KE = (p^2)/2m
k = 2pi/lambda, and delta p = h/lambda 



#13
Dec1004, 03:45 PM

Sci Advisor
HW Helper
P: 2,538

I also get less than 1% uncertainty.




#14
Dec1004, 03:53 PM

P: 138

with what formula




#15
Dec1004, 04:00 PM

Sci Advisor
HW Helper
P: 11,863





#16
Dec1004, 04:03 PM

P: 138

for delta p do you get 6.626 * 10^24?




#17
Dec1004, 04:06 PM

Sci Advisor
HW Helper
P: 11,863





#18
Dec1004, 04:22 PM

P: 138

I'm sorry to keep on testing your patience. So then we solve for k using k = 2pi/lambda, because lambda = delta x, and I get 6.283 * 10^10



Register to reply 
Related Discussions  
Partial Derivation to calculate percentage relative uncertainty. Plz help  Calculus & Beyond Homework  2  
Percentage uncertainty and percentage error  Introductory Physics Homework  1  
[SOLVED] Percentage uncertainty  Introductory Physics Homework  4  
Help! Partial Derivation to calculate percentage relative uncertainty  Calculus  0  
Percentage of Uncertainty  General Physics  5 