(B) What is the de Brogie wavelength (λ) of an electron with a kinetic energy of K. (5%)

9. Determine the electric field E caused by a spherical cloud of electrons with a volume charge density ρ = -ρ₀ for 0 ≤ R ≤ b (both ρ₀ and b are positive) and ρ = 0 for R > b in the free space (the permittivity of the free space is ε₀). (10%) (A) find \(E(R)\) for \(0 \leq R \leq b\)