65. On the dipole axis θ = 0 or π, so
| cos θ| = 1. Therefore, magnitude of the electric field is
|E(r)| =
−
∂V
∂r
=
p
4πε
0
d
dr
1
r
2
=
p
2πε
0
r
3
.
65. On the dipole axis θ = 0 or π, so
| cos θ| = 1. Therefore, magnitude of the electric field is
|E(r)| =
−
∂V
∂r
=
p
4πε
0
d
dr
1
r
2
=
p
2πε
0
r
3
.