862. What is induced polarization and what are its applications? — PSD, Rio de Janeiro, Brazil
An electrically neutral object contains both positive and negative electric charges, however, those opposite charges are equal in amount and therefore cancel one another. But this cancellation doesn't mean that the charges are unaffected by another nearby charge. If you hold an electrically neutral object near an electrically charged object, the charged object will cause a slight rearrangement of the charges in the neutral object. Charges opposite to that of the charged object will shift toward that object while charges like that of the charged object will shift away from that object. The neutral object will acquire an "induced polarization", meaning that it its positive and negative charges are displaced relative to one another and that this displacement is "induced" by the presence of nearby charge. Induced polarization is a common effect and is present whenever lightning is about to strike the ground. As an electrically charged cloud drifts overhead, the objects on the ground acquire induced polarization. Their tops become covered with charge opposite that of the cloud and a lightning strike may occur between the cloud and the oppositely charged top of a tree or building.