The uncertainty in position of an electron equals its own de Broglie wavelength. Using Delta x Delta p ge h/4pi, the minimum fractional uncertainty Delta v/v in its speed is

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The uncertainty in position of an electron equals its own de Broglie wavelength. Using $Δ x Δ p \geq h /4 π$ , the minimum fractional uncertainty $Δ v / v$ in its speed is

Δ p \geq h / (4 π Δ x) = h / (4 πλ) = p /4 π

since

λ = h / p

. Thus

Δ v / v \geq 1/4 π \approx 0.08