Ela asks:

- Magnitude and direction of dipole field depends not only on distance r from centre of dipole,but also on the angle between the position vector rand the dipole moment
phow?- How can centres of positive and negative charge lie on same place and if both have same charge they should become neutral?

Answer:

1. The electric field at a point due to a dipole is given by

Which clearly explains the answer to your question

2. Centre of positive charge means the centre of mass of all the positive charged particles and similarly for the negative charge. If the atom or molecule is symmetric, the two centres of charge will coincide; just like the centre of mass of two concentric hollow spheres. The charges are not at the same point, but their centres of mass coincide. If they do not coincide, it will give rise to an electric dipole or a polar molecule.

the dipole is afterall a system two opposite charges.so basically when we calculate the field due to a dipole we are finding out the RESULTANT electric field due to the positive and negative charge at some point.and since electric field is a VECTOR field direction is important.so when you find the resultant field at a point you need to know the angle between the dipole moment vector and the position vector.the resultant field does depend on the angular position and also the distance.

on the other hand the electric potential due to the dipole depends only on the distance from the dipole.because its not a vector field and is a scalar field.or direction has no meaning to it.

its possible to calculate electric field at any point due to a dipole given the distance from the centre of the dipole and the angle between the dipole moment vector and the position vector,if the distance from the dipole is much bigger compared to the dipole length.

Good work John

2. Off course, they neutralise when charge centers are at the same place. A neutral entity means no field outside the distribution of charge. Remenber that the charge neutralisation doesn’t mean one destroys the another.In so called neutral atoms and the molecules charge centers of the electron cloud and the nucleic distribution lie at the same place. If not it behaves like a dipole.

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