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There are many industrial uses of static electricity. These make use of both repulsion of like charges, and attraction of opposite charges.

Insecticides

Insecticide sprays from aircraft can be electrostatically charged so that they cover a large area. With this method there is less risk that some of the spray will blow away or fall unevenly. The droplets of insecticide are all given the same static charge as they leave the aircraft.

The static drops spread evenly as they all have the same charge and repel each other. They are also attracted to the earth, so will fall quickly and are less likely to blow away.

Photocopiers

Photocopiers also use static electricity to attract the small particles of ink onto the paper in the right places.

The electrostatic precipitator

To clean small particles from smoke before it leaves an industrial chimney, a machine called an electrostatic precipitator will use static electricity to attract the particles.

Dangers of electrostatics

All charged objects can be discharged by being earthed. This may happen safely by connecting them to the earth with a conductor.

If the charge is very large, a spark to the earth may happen unexpectedly. Sparks like this can be dangerous, potentially igniting a fire. A build-up of static charge is a potential danger when refuelling aircraft or vehicles. Fuel running through the pipes can provide the friction needed to create a static charge. To prevent this, aircraft are earthed with a conductor during re-fuelling.

Less dangerous, but sometimes painful, a spark discharge may happen if a charged person touches an earthed conductor. For example, a person dragging their feet across the carpet may become charged. If they then reach out to touch a door handle or another person, there is a spark and they feel a small shock.