Question

A long, straight metal rod has a radius of 4.60 cm and a charge per unit length of 39.8 nC/m. Find the electric field at the following distances from the axis of the rod, where distances are measured perpendicular to the rod's axis. 

(a) 2.50 cm 

(b) 20.0 cm 

(c) 200 cm 

Answer 1

A)

0 (Zero)

Since charge always accumulates on surface. So, field intensity at distance of 2.5 cm is zero.

B)

E = (39.8 x 10^-9)/(2 pi x 8.85 x 10^-12 x 0.20) = 3578.74 N/C

C)

E = (39.8 x 10^-9)/(2 pi x 8.85 x 10^-12 x 2) = 357.87 N/C