Answer:
2.4 * 10^-6 C/m²
Explanation:
The Force experimented by a particle in an electric field will be equal to:
F = E*q
Where E is the magnitude of the electric field and q is the charge of the particle.
The Electric field caused by a parallel plate capacitor will be:
E = σ/ε0
Where σ is the charge density of the plates of the capacitor and ε0 is the Vacuum permittivity constant.
We replace this expression in the expression for force and issolate σ and get that:
σ = F*ε0/q = 0.38 N * 8.854 * 10^-12 F/m / (1.4*10^-6C) = 2.4 * 10^-6 C/m²