## Sapling hw #19

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

jazlynromero2H
Posts: 43
Joined: Wed Sep 30, 2020 10:09 pm

### Sapling hw #19

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 1.4 Å.

Hi! I came across this question on sapling but I am unsure on how to approach it. I was thinking that in order to find the uncertainty in velocity, it will have to be using p=mv, but I am not sure what to do with the angstroms, or what to convert them into. I am also not sure what mass I would be using. Can someone help better explain what to do? Thanks!

Mohamed Mido
Posts: 56
Joined: Wed Sep 30, 2020 9:33 pm

### Re: Sapling hw #19

An Ångstrom is 1x10^-10 meters. Electron mass is 9.11x10^-31 kg. A helium atom's mass is 1 He atom x 1 mol He/6.022x10^23 atoms x 4.00g He/1 mol He = 6.64x10^-27 kg. You will have to use ∆v≥h/(4π)(m)(∆x), with 11 Å being ∆x, and the masses of each particle/atom respectively as m.
∆p can be substituted with m∆v btw

Brianne Conway 1H
Posts: 41
Joined: Wed Sep 30, 2020 9:36 pm

### Re: Sapling hw #19

Like Mohamed said, for questions like this that ask for the minimum uncertainty of something (whether it be position or velocity), you just need to know how to rearrange the ΔxΔp ≥ h/4π equation to solve for what you need. For questions that ask about an electron, a proton, or a neutron, the mass is given on our constants and equations sheet or it might be given in the question (pay attention to units though, you need it to be in kg since planck's constant uses kg). And also like Mohamed said, for questions that ask about individual atoms, make sure to calculate the mass of a single atom instead of using the molar mass given on the periodic table (like I did). Some questions might also ask about a hydrogen molecule (as an example) or something, in which case you'd have to multiply the mass of a single hydrogen atom by 2 to get the mass of an H2 molecule. Basically, just read the questions very carefully.

jessicaosuna_3E
Posts: 42
Joined: Wed Sep 30, 2020 9:51 pm

### Re: Sapling hw #19

I'm doing this question too and U moved the equation around right, but I keep getting the answer wrong. Can somebody walk through it step by step?

Diana Aguilar 2L
Posts: 40
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Sapling hw #19

I was also having a hard time with this problem, but your explanantions helped me a lot on how to go at solving it. Thank you so much!