Hw - #19
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Hw - #19
What is the minimum uncertainty in a helium atom's velocity (Δvmin) if the position is known within 1.5 Å. For this question, I converted the molar mass of Helium (4.0026g) to 6.6 x 10^-24 and converted 1.5Å to 1.5 x 10^-10 . I then plug the given numbers into the equation deltav = h/4pi m deltax. deltav = plancks constant / 4pi( 6.6 x 10^-24)(1.5 x 10^-10). The answer I'm getting is 5.2 x 10^-2 but its telling me I'm wrong, please let me know if you see any errors in my confusion or if my thought process is wrong.
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Re: Hw - #19
Hi,
I think the issue is that the mass you used is in grams but for the equation, the mass needs to be in kg since planck's constant (h) is also in kg. Therefore, for the mass, I used 6.64 x 10^-27 kg and I followed all the same steps as you did and I got 53 m/s as the final answer.
I think the issue is that the mass you used is in grams but for the equation, the mass needs to be in kg since planck's constant (h) is also in kg. Therefore, for the mass, I used 6.64 x 10^-27 kg and I followed all the same steps as you did and I got 53 m/s as the final answer.
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Re: Hw - #19
Yeah, just make sure that when you are doing problems like this, you always convert quantities to SI units immediately so that you don't trip yourself up later on. I made the same mistake and then realized I didn't convert the helium mass from grams to kg.
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Re: Hw - #19
Really happy I found this thread. I didn't know what I was doing wrong. Always gotta make sure to convert to the proper SI units.
Re: Hw - #19
instead of having 6.6x10^-24 as your mass, it should be 0.664x10^-26.
Take the molar mass of helium and divide it by avogadro's number to get g/atom and then convert grams to kg by dividing by 1000 because plank's constant uses kg.
So it should be:
(4g*mol^-1) * (1mol/6.022x10^23) = 0.664x10^-23 g/atom
then g --> kg
(0.664x10^-23g*atom^-1) * (1kg/1000g) = 0.664x10^-26
Then plug that in for mass
Take the molar mass of helium and divide it by avogadro's number to get g/atom and then convert grams to kg by dividing by 1000 because plank's constant uses kg.
So it should be:
(4g*mol^-1) * (1mol/6.022x10^23) = 0.664x10^-23 g/atom
then g --> kg
(0.664x10^-23g*atom^-1) * (1kg/1000g) = 0.664x10^-26
Then plug that in for mass
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