Some websites and textbooks refer to $$\Delta x \Delta p \geq \frac{\hbar}{2}$$ as the correct formula for the uncertainty principle whereas other sources use the formula $$\Delta x \Delta p \geq \hbar.$$ Question: Which one is correct and why?
The latter is used in the textbook "Physics II for Dummies" (German edition) for several examples and the author also derives that formula so I assume that this is not a typing error.
This is the mentioned derivation:
$\sin \theta = \frac{\lambda}{\Delta y}$
assuming $\theta$ is small:
$\tan \theta = \frac{\lambda}{\Delta y}$
de Broglie equation:
$\lambda = \frac{h}{p_x}$
$\Rightarrow \tan \theta \approx \frac{h}{p_x \cdot \Delta y}$
but also:
$\tan \theta = \frac{\Delta p_y}{p_x}$
equalize $\tan \theta$:
$\frac{h}{p_x \cdot \Delta y} \approx \frac{\Delta p_y}{p_x}$
$\Rightarrow \frac{h}{\Delta y} \approx \Delta p_y \Rightarrow \Delta p_y \Delta y \approx h$
$\Rightarrow \Delta p_y \Delta y \geq \frac{h}{2 \pi}$
$\Rightarrow \Delta p \Delta x \geq \frac{h}{2 \pi}$
So: Which one is correct and why?
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