An electric dipole is a pair of point charges with equal magnitude and opposite sign , positive charge q and a negative charge -q) separated by a distance d. We introduced electric dipoles in Example 22-9 (Section 22-7); the concept is worth exploring further because many physical systems, from molecules to TV antennas, can be described electric dipoles. We will also use this concept extensively in our discussion of diel in Chapter 25.

Figure 22-24 shows a molecule of water ~O), which in many ways behaves like an electric dipole. The water molecule as a whole is electrically neutral, but the chemical bonds within the molecule cause a displacement of charge; the result is a net negative charge on the oxygen end of the molecule and a net positive charge on the hydrogen end, forming an electric dipole. The effect is equivalent to shifting one electron only about 4 x 10-11 m (about the radius of a hydrogen atom), but the consequences of this shift are profound. Water is an excellent solvent for ionic substances such as table salt (sodium chloride, NaCl) precisely because the water molecule is an electric dipole. When dissolved in water, salt dissociates into a positive sodium ion (Na”) and a negative chlorine ion (Cl”), which tend to be attracted to the negative and positive ends, respectively, of water molecules; this holds the ions in solution. If water molecules were not electric dipoles, water would be a poor solvent, and almost all of the chemistry that occurs in aqueous solutions would be impossible. This includes all of the biochemical reactions that occur in all of the life on earth. In a very real sense, your existence as a living being depends on electric dipoles!

electric dipole experience when placed in an external electric field (that is, a field set up by charges outside the dipole)? Second, what electric field does an electric dipole itself produce?


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