One practical application of electrostatics is the smoke removal from thermoelectric power stations. This is done by the so called electrostatic smoke filter (or precipitator) which function on the following principle: near the top of the chimney there is a network of electrodes having sharp spikes at their ends. At a certain distance a set of large parallel plates is placed parallel to the smoke flow. A very high voltage source is connected between the electrodes and the plates. Because of the electric voltage, the electric field lines are denser near the spiked ends of electrodes and the smoke particles are ionized in their way out of the chimney. When these charged particles pass between the larger plates they are collected by the electric field and thus the smoke is removed and disappears from the top of the chimneys.
A second practical application can be found in the copier machine. The paper to be copied is subjected to ultraviolet light. This light is reflected by the white zones of the paper on to a Selenium cylinder that rotates under the paper. By external photoelectric effect (Einstein got his Nobel prize for discovering it) the cylinder charges electrically, forming on it a potential relief that resembles the paper print. Then, the charged cylinder attracts toner (in the form of a black dust) on it, having the same pattern as the print on the original paper. This toner is transferred by contact to a second paper and by heating, it adheres to it, forming the copy.