Question

To prevent dust and soot particles from polluting the atmosphere, industry often employs static electric charges in their smokestacks.

Explain the physics principle involved in this application.

Answer 1

The physics principle behind this is electrostatics. You can easily demonstrate it by rubbing a balloon repeatedly on your sweater until it sticks by the sheer force of static electricity. As you rub the balloon, electrons break free from the molecules of rubber that are inside it and gather on your sweater. The balloon (losing electrons) becomes positively charged while your sweater (gaining electrons) becomes negatively charged. Because opposite charges attract, the balloon sticks to your sweater.

Similarly, Smoke consists of microscopically tiny particles of soot (unburned carbon) and dust. If we can somehow make these soot or dust charged then they can be easily extracted from the smoke using charged plate of opposite charge. This phenomenon is purely electrostatic. These types of smoke precipitators are called electrostatic smoke precipitators.

Electrostatic smoke precipitators work by forcing smoke past two electrodes, which take the form of metal wires, bars, or plates inside a pipe or smokestack. The first electrode is charged to a very high negative voltage. As the dirt particles move past it, they pick up a negative charge. Higher up the pipe, there's a second electrode consisting of metal plates charged to a high positive voltage. Since unlike charges attract, the negatively charged soot particles are attracted to the positively charged plates and stick there. The gas rising above the smokestack is now free from soot and dust. The upper plate where the soot and dust are attracted can be cleaned time to time and used further.