## Particle as a wave

### Task number: 4404

Assume that the uncertainty of a particle’s location is equal to its de Broglie wavelength. What would be the minimum uncertainty of its momentum in this case? What part of the momentum does this uncertainty represent? Consider motion in one dimension.

#### Hint

De Broglie wavelength of the particle is inversely proportional to its momentum. How exactly?

#### Solution

We know that we can express the uncertainty of the location Δ

\[\Delta x=\frac{h}{p} .\]*x*asThe location’s uncertainty Δ

\[\Delta x\,\cdot\,\Delta p\ge\frac{\hbar}{2} .\]*x*and uncertainty of momentum Δ*p*are tied together through the Heisenberg principle of uncertainty:From that we can derive

\[\Delta p \ge \frac{\hbar}{\,2\Delta x}=\frac{\hbar p}{2h}=\frac{\hbar p}{4\pi \hbar}=\frac{p}{4\pi}\,\dot{=}\, 0.08\,p .\]#### Answer

The smallest possible uncertainty of the particle’s momentum is approximately 8 % of its value.