Applications of Electrostatics

Question 1

Describe and explain agricultural spraying

Answer 1

1. Pest can be very harmful to the development of plants.
2. They feed on the leaves of plants, usually living on the underside of the leaves.
3. This makes spraying with pesticides a tricky process.
4. A technique has been developed where the nozzle of the spray is connected to a high voltage supply.
5. This high voltage supply has two effects. It charges the spray droplets positively and induces an opposite charge on the ground and the plants.
6. The causes the spray droplets to be attracted to both sides of the leaves.
7. This technique also prevents wastage during the spraying process.

Question 2

Describe and explain the principles behind dust extraction.

Answer 2

1. Dust particles may be extracted from the flue gases released by industrial chimneys by using the electric field that exists between a wire and a metal cylinder.
2. The inner walls of the chimney is fitted with a cylindrical piece of metal.
3. A series of wires at high negative voltages are mounted inside the cylinder.
4. A large electrical field exists between the wires and the cylinder.
5. The electric field removes electrons from some of the air molecules, thus forming ions.
6. Free electrons in the air close to the wire are accelerated away.
7. Electrons and negative ions in the air become attached to the dust particles.
8. The charged dust particles are then attracted to the inner walls of the cylinder.
9. Hammers are used to strike the cylinder to dislodge dust particles, which then fall into the traps at the bottom of the chimney.

Question 3

Describe and explain the principles behind photocopiers and laser printers.

Answer 3

1. In photocopiers, a light-sensitive cylindrical drum is charged positively by a charged grid.
2. An image of the document being copied is projected on to the drum.
3. The areas of the drum exposed to light lose their positive charge.
4. A negatively charged powder, called toner is dusted over the drum.
5. The toner is attracted to the positively charged image.
6. A sheet of paper then receives a positive charge as it passes over the grid.
7. The positively charged paper attracts toner from the drum and an image is formed on it.
8. The image is made permanent by warming the final product.
9. A laser printer uses a series of mirrors and lenses to focus it on the light sensitive cylindrical drum to write the image to be printed on the drum.

Question 4

Describe and explain the principles of electrostatic paint spraying.

Answer 4

1. Car manufactures use electrostatics to paint their vehicles.
2. As the paint leaves the nozzle of the sprayer, the droplets are given a charge.
3. Since all the droplets have the same charge, they repel each other so that the paint spreads out to form a large even cloud. 4. The body of the car is charged with an equal and opposite charge.
4. The result is that the paint sticks to the surface of the car tightly and less paint is wasted in the process.

Question 5

Explain why touching a door handle can result in an electrical shock?

Answer 5

1. Our bodies may become charged by friction.
2. The touching a metal door handle causes the charge to flow to the handle.
3. The flow of charge results in an electric current and you experience an electric shock.

Question 6

Explain the precautions taken by aircrafts when refueling.

Answer 6

1. A conducting cable is connected between the aircraft and the fuel tanker.
2. This ensure that they are at the same electrical potential.
3. This ensures that no sparks arise.
4. A spark can ignite the fuel causing a dangerous explosion.

Question 7

Explain how is lightning produced in clouds?

Answer 7

1. In thunderstorms, clouds are charged as they move through the atmosphere.
2. Negative charges tend to build up on the bottom on the clouds.
3. This repels the negatives charges in building towards the earth induces a positive charge at the tops of these buildings and trees etc.
4. This large electric field created between the cloud and the building causes air molecules to ionise.
5. Electrons are stripped from the air molecules and ions are produced.
6. The flow of the electrons towards the buildings and the ions towards the clouds produces very large currents which can start fires, damage the building.

Question 8

Explain how we can prevent damage to buildings by lightning.

Answer 8

1. A lightning rod, a thick piece of copper strip fixed to an outside wall reaching above the highest part of the building.
2. The part of the rod above the highest part of the building consisting of several sharp spikes.
3. The other end of the copper strip is buried in the earth below.
4. When lightning strikes, it usually strikes the highest point of a building.
5. The current travels along the path of least resistance to the earth, without damaging the building.