51. A small object with electric dipole moment p is placed in a
nonuniform electric field E # E(x)ˆi. That is, the field is in
the x direction and its magnitude depends on the coordinate
x. Let 2 represent the angle between the dipole
moment and the x direction. (a) Prove that the dipole
feels a net force
in the direction toward which the field increases. (b) Consider
a spherical balloon centered at the origin, with
radius 15.0 cm and carrying charge 2.00 %C. Evaluate
dE/dx at the point (16 cm, 0, 0). Assume a water droplet at
this point has an induced dipole moment of 6.30ˆi nC+m.
Find the force on it.