# Dipole in dielectric

1. Mar 22, 2006

### sachi

We have a dipole in a vaccuum cavity inside an otherwise infinite LIH dielectric.
We assume form Vin = Arcos(theta) + B/(r^2) * cos(theta)
Vout = C/(r^2) * cos(theta)
We are told that "as r tends to 0 the field must approach the dipole field".
I'm not sure if they are talking about the E-field or the potential, as the E-field does not appear to tend to a dipole field as r tends to zero (if you differentiate Vin wrt r to get the E-field, you find a term Acos(theta) which does not tend to zero as r tends to zero. therefore we don't get a purely dipole type field. is it legitimate to let r tend to zero first, then perform the differentiation to get the E-field, or are they just talking about the potential anyway in the first place?)