A slit narrows from 100nm to 10nm. How does the diffraction spread change?

Δx decreases by 10×, so Δp must increase by 10× — much wider spread.

An electron is confined in a 1nm box. What is its minimum kinetic energy?

Δx=1nm → Δp ≥ ℏ/(2×10⁻⁹) → KE = (Δp)²/(2m_e).

Why does measuring which-slit a photon goes through destroy interference?

Which-path information collapses position superposition — you've made it a particle, not a wave.

Pro 🔒~25 min

Quantum Measurement

Explore how measurement affects quantum systems

How it works

Quantum Measurement demonstrates a key principle: The Heisenberg Uncertainty Principle states that position and momentum cannot both be precisely known simultaneously: Δx·Δp ≥ ℏ/2. The Heisenberg Uncertainty Principle states that position and momentum cannot both be precisely known simultaneously: Δx·Δp ≥ ℏ/2. This is not a measurement limitation but a fundamental property of quantum states. Narrowing a slit (precise position) causes wider diffraction (uncertain momentum). The double-slit experiment shows that measuring which-path information destroys the interference pattern — measurement irreversibly disturbs the quantum state.

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Step-by-step

Adjust slit width to control position uncertainty.
Observe how the diffraction pattern widens (momentum uncertainty increases).
Enable which-path detection to see interference disappear.
Use the momentum spectrum to verify the uncertainty relation.

Key formulas

$\Delta x \cdot \Delta p \geq \frac{\hbar}{2}$ Heisenberg Uncertainty Principle
$\Delta E \cdot \Delta t \geq \frac{\hbar}{2}$ Energy-time uncertainty
$\lambda = \frac{h}{p}$ de Broglie wavelength

Frequently asked questions

A slit narrows from 100nm to 10nm. How does the diffraction spread change?: Δx decreases by 10×, so Δp must increase by 10× — much wider spread.
An electron is confined in a 1nm box. What is its minimum kinetic energy?: Δx=1nm → Δp ≥ ℏ/(2×10⁻⁹) → KE = (Δp)²/(2m_e).
Why does measuring which-slit a photon goes through destroy interference?: Which-path information collapses position superposition — you've made it a particle, not a wave.