An infinitely long nonconducting cylinder of radius R = 2.00 cm carries a uniform volume charge density of Calculate the electric field at distance r = 1.00 cm from the axis of the cylinder. (ε0 = 8.85 × 10-12 C2/N ∙ m2)

Respuesta :

Answer:

[tex]E= 1.13*10^9\rho \: \: N/C[/tex] where [tex]\rho[/tex] is the volume charge density.

Explanation:

Since the volume charge density is not given, I will just call it [tex]\rho[/tex].

Gauss's law says

[tex]\oint_S {E \cdot dA = \dfrac{Q_{inside}}{{\varepsilon _0 }}}.[/tex]

To evaluate this integral, we choose a cylindrical Gaussian surface which is concentric with the nonconducting cylinder.

Let [tex]r[/tex] be the radius of the Gaussian cylinder, and [tex]l[/tex] be its length, then the right side of the Gauss's law gives

[tex]\oint_S E\cdot dA=E(2\pi rl)[/tex]

Notice that we only count the lateral area of the cylinder because the sides of the cylinder are perpendicular to [tex]E[/tex], and therefore, give [tex]E\cdot dA=0[/tex].

Now we turn to the right side of Gauss's law.  

Since [tex]r<R[/tex], the charge enclosed by the Gaussian surface is

[tex]Q_{enc}= \rho*V= \rho*(\pi r^2)l[/tex]

which makes the right side

[tex]\dfrac{Q_{enc}}{{\varepsilon _0 }}} = \dfrac{\rho \pi r^2l}{\varepsilon _0}[/tex]

Thus the Gauss's law becomes

[tex]E(2\pi rl )=\dfrac{\rho \pi r^2l}{\varepsilon _0}[/tex]

simplifying a and solving for [tex]E[/tex] we get:

[tex]\boxed{E= \dfrac{\rho r }{\varepsilon_0 }. }[/tex]

Putting in [tex]\varepsilon_0 = 8.85*10^{-12} C^2/N*m^2[/tex] and [tex]r=0.01m[/tex], we get:

[tex]\boxed{ E= 1.13*10^9\rho \: \: N/C}[/tex]