Suppose a stream of negatively charged powder was blown through a cylindrical pipe of radius R = 7.5 cm. Assume that the powder and its charge were spread uniformly through the pipe with a volume charge density rho. (a) Find an expression for the electric potential as a function of the radial distance r from the center of the pipe. (The electric potential is zero on the grounded pipe wall.) (b) For the typical volume charge density rho = -3.7 × 10-3 C/m3, what is the difference in the electric potential between the pipe's center and its inside wall?

Respuesta :

Answer:

A) [tex]E =\frac{\rho r}{2\epsilon}[/tex]

B) [tex]v = 58.7923\times 10^4 V[/tex]

Explanation:

a) using Guass law

[tex]\oint E.dA = \frac{q_{enclosed}}{\epsilon_o}[/tex]

[tex]EA = \frac{q_{enclosed}}{\epsilon_o}[/tex]

[tex]E =  \frac{q_{enclosed}}{A \epsilon_o}[/tex]

Here[tex] A is = 2\pi rL[/tex]

[tex]E =  \frac{q_{enclosed}}{(2\pi rL) \epsilon_o}[/tex]

Volume charge density is given as

[tex]\rho = \frac{q_{enclosed}}{volume}[/tex]

net charge is given as

[tex]q_{enclosed} = \rho \times volume[/tex]

therefore [tex]E =  \frac{ \rho \times (L\pi r^2)}{(2\pi rL) \epsilon_o}[/tex]

[tex] VOLUME  =  L\pi r^2[/tex]

After solving electric field equation we get

[tex]E =\frac{\rho r}{2\epsilon}[/tex]

b) electric potential difference is given as

[tex]v_{wall} - v = - \int_{r}^{R} Edr[/tex]

[tex]0 - v = - \int_{r}^{R} E dr[/tex]

[tex]v = \int_{r}^{R} Edr[/tex]

[tex] = \int_{r}^{R} (\frac{\rho r}{2\epsilon}) dr[/tex]

[tex] = \frac{\rho}{4\epsilon} (R^2 - r^2)[/tex]

at r = 0

[tex]v = \frac{- 3.7 \times 10^{-3} \times 0.075^2}{4\times (8.85\times 10^{-12}}[/tex]

[tex]v = 58.7923\times 10^4 V[/tex]