The electric field must be zero inside a conductor in electrostatic equilibrium,
ID: 1566094 • Letter: T
Question
The electric field must be zero inside a conductor in electrostatic equilibrium, but not inside an insulator. It turns out that we can still apply Gauss's law to a Gaussian surface that is entirely within an insulator by replacing the right-hand side of Gauss's law, Qin/0, with Qin/ , where is the permittivity of the material. (Technically, 0 is called the vacuum permittivity.) Suppose a long, straight wire with linear charge density 250 nC/m is covered with insulation whose permittivity is 2.50.
What is the electric field strength at a point inside the insulation that is 3.0 mm from the axis of the wire?
Explanation / Answer
given
lamda = 250 nC/m
= 250*10^-9 C/m
at r = 3 mm = 3*10^-3 m
electric field, lamda = lamda/(2*pi*epsilon*r)
= 250*10^-9/(2*pi*2.5*8.854*10^-12*3*10^-3)
= 6.0*10^5 N/c