What does it mean when two point charges form a dipole a small distance away from each other?

Question

Charles Aeschliman · Accepted Answer

Small refers to sufficiently close together.

If two charges are too far apart, they are essentially independent charges (which does not imply that they aren't interacting). Two charges can only interact well enough to form a dipole if they are close enough together.

Take into consideration the two point charges' coulombic interaction:

#V(vecr) = (q_1 q_2)/(4piepsilon_0vecr_(12)#

where #q_i# is the charge of particle #i#, #epsilon_0 = 8.854 xx 10^(-12) "F"cdot"m"^(-1)# is the vacuum permittivity constant, and #vecr_(12)# is the radial separation between two particles.

This means the coulombic potential of the two charges depends on the distance between them and the charges' magnitudes. Large #r#, small potential. Large enough potential, and a dipole forms, where a dipole between two point charges of charge #pmq# is defined as:

#vecmu_(12) = qcdotvecr_(12)#

An example of a small charge is #e^(-) = 1.6022 xx 10^(-19) "C"#.

An example of "small" for molecules is a few #stackrel("o")("A")#. The bond length of the #"OH"# bond in #"H"_2"O"# is #0.958# #stackrel("o")("A")#, where #1# #stackrel("o")("A") = 10^(-10) "m"# is an angstrom.

Charles Aeschliman · Answer

undefined When two point charges form a dipole a small distance away from each other, it means they have opposite charges and are separated by a short distance.