# What else do I need to know to calculate the de Broglie wavelength of an electron moving at 80% the speed of light?

Aug 11, 2014

You need to know the value of Planck's constant, the mass of the electron, and the speed of light.

You also need to know the de Broglie equation.

You use the equation

λ = h/(mv)

$h$ = 6.626 × 10⁻³⁴ kg·m²s⁻
$m$ = 9.11 × 10⁻³¹ kg
$v$ = 0.80 × 2.998 × 10 ⁸ m·s⁻¹ = 2.4 × 10⁸ m·s⁻¹
λ = h/(mv) = (6.626 × 10⁻³⁴"kg·m²s⁻¹")/(9.11 × 10⁻³¹"kg" × 2.4 × 10⁸"m·s⁻¹") = 3.0 × 10⁻¹² m = 3.0 pm