## hiesenberg uncertainty principle, h or hbar?

i've seen both:

ΔxΔp >= h/2

and

ΔxΔp >= hbar/ 2

used, and i'm not sure which is correct. my physics textbook uses h/2, but wiki and other online rescources seem to use hbar/2

do they apply to different situations? (if so, where do you use hbar and where do you use h?) or is one of them outdated?

 PhysOrg.com physics news on PhysOrg.com >> Promising doped zirconia>> New X-ray method shows how frog embryos could help thwart disease>> Bringing life into focus
 Recognitions: Science Advisor No, the only generally correct statement is about standard devitians of two observables. For any (pure or mixed) state, one has $$\Delta A \Delta B \geq \frac{1}{2} |\langle [\hat{A},\hat{B}] \rangle|.$$ Since for position and momentum components in the same direction, you have $$[x,p]=\mathrm{i} \hbar$$ you have $$\Delta x \Delta p \geq \hbar/2.$$ Other uncertainty relations are found in the literature from hand-waving arguments using other uncertainty measures than the standard deviation!
 so if i'm understanding correctly, if you use standard deviation, it's always hbar/2, but if you use other measures of spread then it could be different?

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