The figure below is a section of a conducting rod of radius R1 = 1.30 mm and len
ID: 1900401 • Letter: T
Question
The figure below is a section of a conducting rod of radius R1 = 1.30 mm and length L = 11.00 m inside a thick-walled coaxial conducting cylindrical shell of radius R2 = 10.0R1 and the (same) length L. The net charge on the rod is Q1 = +2.80 10-12C that on the shell is Q2 = ?4.00Q1. (a) What is the magnitude E of the electric field at a radial distance of r = 2.00R2? (b) What is the direction of the electric field at that radial distance?(c) What is the magnitude E of the electric field at a radial distance of r = 4.50R1? (d) What is the direction of the electric field at that radial distance? (e) What is the charge on the interior surface of the shell? (f) What is the charge on the exterior surface of the shell?Explanation / Answer
a. Outside the shell, the rod has net charge of: (2.8-4*2.8) *10^-12C = -8.4*10^-12C thus lemda= (-8.4/11) *10^-12C/m =0.794 *10^-12C/m for rod geometry: |E| = 2*k*lemda/r =(2*9*10^9*0.794*10^-12)/(2*10*1.1*10^-3) =0.649 N/C b. since the point lies between R1 and R2 Q1=2.8*10^-12C lemda=2.545*10^-13 C/m |E|= 2*k*lemda/r =0.754N/C c. Q1+Q2 = -8.4*10^-12C