It was shown in Example 21.11 (Section 21.5) in the textbook that the electric f

Question

It was shown in Example 21.11 (Section 21.5) in the textbook that the electric field due to an infinite line of charge is perpendicular to the line and has magnitude E=/20r. Consider an imaginary cylinder with a radius of r = 0.145 m and a length of l = 0.455 m that has an infinite line of positive charge running along its axis. The charge per unit length on the line is = 4.00 C/m .What is the flux through the cylinder if its radius is increased to r= 0.540 m ? What is the flux through the cylinder if its length is increased to l= 0.760 m ?

Explanation / Answer

field is radially outward from wire.

hence flux will be through curved surface.

flux through flat circular surface will be zero.

when r = 0.540 m and L = 0.455

flux = E. (2 pi r L)

= (lambda / 2 pi e0 r) ( 2pi r L) = (lambda L) / (e0 )

hence flux is independent of circle.

flux = (4 x 10^-6 x 0.455 ) / (8.854 x 10^-12) =205556.81 Wb

when L = 0.760 m

flux = (4 x 10^-6 x 0.760 ) / (8.854 x 10^-12) = 343347.64 Wb

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