In preparation for an experiment that you will do in your introductory nuclear p
ID: 1461109 • Letter: I
Question
In preparation for an experiment that you will do in your introductory nuclear physics lab, you are shown the inside of a Geiger tube. You measure the radius and the length of the central wire of the Geiger tube to be 2.0 X 10^-4 m and 1.2 X 10^-1 m, respectively. The outer surface of the tube is a conducting cylindrical shell that has an inner radius of 1.5 X 10^-2 m. The shell is coaxial with the wire and has the same length (0.12 m). (a) Calculate the capacitance of your tube, assuming that the gas in the tube has a dielectric constant of 1.00. F (b) Calculate the value of the linear charge density on the wire when the potential difference between the wire and shell is of 1.20 kV. C/mExplanation / Answer
a)
given
a = 2*10^-4 m
b = 1.5*10^-2 m
L = 0.12 m
Capacitnace of cyllinrical capcacitor, C = 2*pi*epsilon*L/ln(b/a)
= 2*pi*8.854*10^-12*0.12/ln( 1.5*10^-2/(2*10^-4))
= 1.55*10^-12 F
b) Total charge on capacitor, Q = C*V
= 1.55*10^-12*1200
= 1.85*10^-9 C
linear charge density on the wire = Q/L
= 1.85*10^-9/0.12
= 1.54*10^-8 C/m