[rleung]

Hi,

When they say that a particle travels at 3x10^7 + or - 0.1x10^7, 0.1x10^7 is the uncertainty in velocity that we use in the equation /_\v*m*/_\x > h/4pi, right?  Thanks so much.

Ryan

[syko sykes]

Hi,

When they say that a particle travels at 3x10^7 + or - 0.1x10^7, 0.1x10^7 is the uncertainty in velocity that we use in the equation /_\v*m*/_\x > h/4pi, right?  Thanks so much.

Ryan

i don't know what "/_\v*m*/_\x > h/4pi" is referring to but i think the uncertanity is because the density of the substance the particle is traveling through varies slightly which will slightly alter it's velocity.

Also, that number looks very similar to the speed of light. Did you mean 3x10^8 m/s?

[rleung]

/_\ is delta (sorry, I couldn''t input that character here

Ryan

[mike]

?

[syko sykes]

oh... it's all starting to make more sense now. While i've never used that equation before I'm pretty sure that what you're saying is correct. The 0.1x10^7 would kind of be like the percent error of that velocity. So the actual velocity should be somewhere between 2.9x10^7 and 3.1x10^7.

Could you clarify the equation a bit more:
i got that ?V is change in velocity and m is mass
what is ?x and h- change in position and height?
and would i be correct to assume that pi is referring to 3.14159..

[xiankai]

actually, the ?v means the uncertainity in velocity, and ?x being the uncertainity in the cartesian coordinates of the particle being measured, or more better known as the position. (?v)(m) is the same as ?p which is more commonly known, where p=mv and is the momentum.

and as for the uncertainity in your given speed of light, is NOT the application of the heisenberg's uncertainity principle. it is merely the rounding of the speed of light to one decimal places. it should be regarded more as (3.0±0.1) x 10⁷ m s^-1

remember, the existence of the photon has not been seen directly so far, merely based on empirical results like black-body radiation and the photelectric effect. this suggests the uncertainity of the position of the photon is very huge, and that would make the uncertainity for speed of light very small.

[rleung]

Thanks so much.  I was confused at first because I usually see ?v represented as something like 3.0 x 10^7 ± 1% as opposed to them defining it directly for you.  Thanks again!