Hello , I post a message because I will need help with this exercise I would like to knowif my answer are good, I'm french : An infinite hollow cylinder charge is constituted of a sheath whose outer limits are R2 and R3. Wearing a uniform charge density ρ Question 2)calculate the total electric field E at any point M ( r ,θ, z) into space. 3) Give the appearance of E according to the relevant variable . 4 ) Calculate the electrostatic energy carried by a cylinder length L. And my answers are: 2)There are 3 cases: The first r<R2 Whe can say that : And Er(r)=0 because ρ=0. Second and third case: 3) I had a problem to place A and B because I do not know how far they must be put to the origin O ( 0,0,0) . I do not know either the distance required between R2 and R3 on the drawing or the shape of the curve. 4) and Ep=0 beacause ρ=0. Also the beginning of my reasoning is here(in french,but the only the formulas are important).