When a potential difference of 150 V is applied to the plates of parallel-plate capacitor, the plates carry a surface charge density of 30 nc/cm^2. The spacing between the plates (in μm) is: a) 2.2 b) 1.1 c) 4.4 d) 6.6

s = 4.425*10^-6 μm

Explanation:

C = Q/V

but also:

C = ∈*A/s

for A being the area of the plates, the:

Q = 30 nc / (cm^-2)

then:

Q = (30*10^-9) * A/V = ∈*A/s

∈ = 8.85 pF/m

that is: (30*10^-9) / V = (8.85*10^-12) / s

then, s = (8.85*10^-12) (150) / (30*10^-9)

= 4.425*10^-6 μm

Therefore, the spacing between the plates is 4.425*10^-6 μm.