22.3.4—Λ = h / p

Use λ=h/p with h=6.63×10⁻³⁴ J s and momentum p in kg m s⁻¹.

If speed is known and v is far below c, calculate p=mv first; keep units consistent before comparing λ with a slit or lattice spacing.

For a 9.11×10⁻³¹ kg electron moving at 2.0×10⁶ m s⁻¹, λ is about 0.36 nm, comparable with atomic spacings.

Do not substitute kinetic energy directly for p unless you first use the appropriate relation; rounding p too early can distort λ.