Find the potential difference across the plates given plate area, charge, and distance between plates? Why is k excluded from equation?

Find the potential difference across the plates given plate area, charge, and distance between plates? Why is k excluded from equation?

Area= #0.2 m^2#
Distance=#1mm#
Charge (both plates)=#4E-6C#
#ε_0=8.85E-12#
#k=9E9#
A) 0
B) #4E-2#
C) #1E2#
D)#2E2#
E)4#E8#
The answer is D). I was more confused with how to get the right answer.
I attempted to derive two equations to get V:
#C_(par.plates)=(kε_0A)/d#
and
#V=Q/C#
to
#V=(Qd)/(kε_0A)#
But when I tried to solve for V it was incorrect. An internet search told me my equation was mostly correct, except k wasnt part of the equation. Why is this? Youve got your constants mixed up.
Here k is not the Coulomb constant, which is the number you use. Rather, it is the relative permittivity of the dielectric. If it is air, k = 1.00058986 pm 0.00000050 :slight_smile:
Think C = (color(red)(epsilon_r) epsilon_o A)/(d) with epsilon_r = 1