R - Galileo and Einstein

Field from a Uniform Line of Charge
• The strategy is to find the field
z from a bit dz of the wire, then
do an integral over the whole
wire.
kdq kdz kd R
tan
kd
dE
2 2 2 2
r r R sec R
• For an infinite wire, the net field
must be directly away from the
wire, so multiply by cos and
integrate over all z :
E
k
R
/2
/2
cosd
2k
R
dE
• q
dE
in
r
Rsec
P
R
from charge
d Rtan
z-axis
dz
z
Rtan
O