## Sapling 26

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

Karina Rodriguez 2H
Posts: 50
Joined: Wed Sep 30, 2020 9:34 pm

### Sapling 26

"What is the minimum uncertainty in an electron's velocity (Δvmin) if the position is known within 11 Å.
What is the minimum uncertainty in a helium atom's velocity (Δvmin) if the position is known within 1.1 Å."
I'm unsure of what my mistake is. I plugged in the given values to my manipulated equation (Δv > h/(4pi)(mass of electron)(Δx)

Sondia Luong 1C
Posts: 59
Joined: Wed Sep 30, 2020 10:01 pm
Been upvoted: 1 time

### Re: Sapling 26

Your plug and chug equation is correct, so maybe you didn't convert angstroms to meters? For the first question asking for the minimum uncertainty in an electron's velocity, you would use the mass of an electron in the denominator, but you would have to use the mass of a helium atom for the second question because they are asking for the minimum uncertainty in a helium atom's velocity. I used 6.646 x 10^-27 kg for the mass of a helium atom and got the question correct. Hope this helps!

SophiaJenny3I
Posts: 87
Joined: Wed Sep 30, 2020 9:56 pm
Been upvoted: 1 time

### Re: Sapling 26

Hi! I had the same setup as you. Where you may be having trouble is plugging it into your calculator like that. To get the right answer, you should plug in h/(4pi x mass of electron x Δx). This ensures you're not multiplying just h/4pi by these factors. Also, make sure to convert 11 Å into m, you should get 11x10^-10 or 1.1x10^-9, depending on how you like to convert it.
Here's how I solved the first part using your setup:
Δv > h/(4pi x 9.109x10^-31 kg x 11x10^-10 m)
Also, based on the sig figs given in the problem your answer should have two. I just put mine in scientific notation as 5.3x10^4 for the first part.
Hope this helps!

t_rasul2I
Posts: 58
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Sapling 26

Hi! I think you might not have converted your units and/or may have plugged your answer into the calculator incorrectly like the previous comments said. You set up the initial problem variables correctly though.

Melanie Lin 3E
Posts: 55
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Sapling 26

Hi Karina!
Like the previous replies, you likely forgot to use parenthesis to separate one value when dividing or some similar typing error on the calculator. It happens to the best of everyone so just make sure you double check your entries during exams!

Ke Huang 2G
Posts: 74
Joined: Wed Sep 30, 2020 9:35 pm

### Re: Sapling 26

I failed many times on this one too. If you got everything to put in the equation, make sure that you have the right units for mass and velocity, which should be kg and m/s.

Posts: 50
Joined: Wed Sep 30, 2020 10:01 pm

### Re: Sapling 26

I was having trouble with this one as well but I finally figured out it was due to the fact that I was not converting Angstroms correctly. Also make sure to be particular about how you enter equations such as this one into your calculator, because I got a few wrong answers since I was typing it in wrong.

Ivan Chen 2H
Posts: 58
Joined: Wed Sep 30, 2020 9:48 pm

### Re: Sapling 26

I kept getting this problem wrong as well until I realized my unit conversions were incorrect. It's important to make sure that mass is in kg and position in meters.

Yuehan_Wu_3K
Posts: 52
Joined: Wed Sep 30, 2020 9:41 pm

### Re: Sapling 26

The equations you use are right。 I think the things you need to pay attention to is the units and that you need to convert the mass unit of helium to mass of the atom using the avogadro constant.