How Does Gauss's Law Calculate Charge on a Cylindrical Shell?

[qwerty123]

I am stuck on this one. I apprciate your help greatly.

A cyllindrical shape of radius 7cm and length 240 cm has its charge uniformly distributed on its curved surface.The magnitude of the electric field at a point 19cm radially outward from its axis (measure from the mid point of the shell) is 36.0KN/C.Find the net charge on the shell.

PLZ show me the light. the part that says 19cm from the axis sounds fishy

 

[Nylex]

What have you done so far? Any thoughts at all? What's wrong with the 19 cm from the axis bit? Seems perfectly reasonable to me.

 

[James R]

Gauss's law will only give an approximate answer for a cylinder of finite length. However, that may be good enough for your purposes here.

How can you use Gauss's law to find the electric field at any distance from the cylinder's axis? Have you done that, yet?

 

[qwerty123]

well, i found the electric field to be...

E= (2KQ)/(Lr) but they want me to solve for Q not for E so...

Q= (ERL)/(2K) --------> Q=(36x10^3)(.19m)(2.40m) / (2)(9x10^9)

Q=9.12x10^-7


i did this but could you double check. i checked in the back of the book, answer is correct but i am not sure if this is the right wa to do it bcause sometimes I get the right answer but not doing it the way it is supposed to.

 

[James R]

Looks ok to me. Of course, I don't know how you arrived at your first expression...