Uses of electrostatics

Question 1

What does a dust precipitators remove?

Answer 1

A dust precipitator removes harmful particles from a chimneys of factories and power stations that pollute the atmosphere.

Question 2

How does a precipitator remove dust?

Answer 2

• A metal grid (or wires) is placed in the chimney and given an electric charge from a high-voltage supply.
• Plates inside the chimney are earthed and gain the opposite charge to the grid.
• As the dust particles pass close to the grid, they become charged with the same charge as the grid.
• Like charges repel, so the dust particles are repelled away from the wires. They are attracted to the oppositely charged plates.
• At intervals the plates are vibrated and the dust falls down to a collector.

Question 3

What happens to dust in the precipitator?

Answer 3

• The dust particles gain or lose electrons to become charged.
• The charge on the dust particles induces a charge on the earthed metal plate.
• Opposite charges attract so the dust is attracted to the plate.

Question 4

How is static used in in paint spraying?

Answer 4

• The spray gun is charged.
• All the paint particles become charged with the same charge.
• Like charges repel, so the paint particles spread out giving a fine spray.
• The object to be painted is given the opposite charge to the paint.
• Opposite charges attract, so the paint is attracted to the object and sticks to it.
• The object gets an even coat, with limited paint wasted.

Question 5

If the object to be painted is not charged, the paint moves onto it but:

Answer 5

• The object becomes charged from the paint, gaining the same charge.
• Further paint droplets are repelled away from the object.
• Therefore the object to be painted is given an opposite charge to the paint. If the paint is negatively charged, having gained electrons, the object should be positively charged, by losing electrons.

Question 6

What is defibrillation?

Answer 6

Defibrillation is a procedure to restore a regular heart rhythm by delivering an electric shock through the chest wall to the heart.

Question 7

What happens in debrillation?

Answer 7

• Two paddles are charged from a high-voltage supply.
• They are placed firmly on the patient’s chest to ensure good electrical contact.
• Electric charge is passed through the patient to make their heart contract.
• Great care is taken to ensure that the operator does not receive an electric shock.

Question 8

If a defibrillator is switched on for 5 milliseconds, the power can calculated from:

Answer 8

power = energy/time = 400/0.0005 = 80,000 W