Bragg's Law
X-ray diffraction from crystal planes
Formula
n λ = 2 d sin θ
- n = order of diffraction (1, 2, 3...)
- λ = X-ray wavelength (m)
- d = spacing between crystal planes (m)
- θ = angle of incidence
Example
Given: λ = 1.54 Å (Cu Kα), θ = 15°, n = 1.
d = n λ / (2 sin θ)
d = (1 × 1.54 Å) / (2 × sin 15°)
d ≈ 1.54 / (2 × 0.2588) ≈ 2.98 Å
Answer: d ≈ 2.98 Å
Applications
- Determine crystal structure and lattice parameters.
- Identify compounds via powder diffraction patterns.
- Constructive interference occurs when path difference = nλ.