1. Application of electrostatics
Photocopying
Working principle: attraction force between opposite charges
original document
light-sensitive drum
lamps
paper

2. The photocopying process Step 1 Step 2
original document
positive charges
Image of the document is projected onto the light-sensitive drum.
lens
The light-sensitive drum is positively charged.
The areas exposed to light lose positive charges.

3. Step 3
Step 4
Negatively charged carbon powder is attracted onto the positively charged paper.
Negatively charged carbon powder adheres to the positively charged areas.
paper

4. Step 5 hot rollers copied document
The carbon powder is fixed onto the paper.

5. Electrostatic precipitator
is used in a coal-fired power station.
removes the dust and the ash produce before escaping through the chimney.
is installed at the bottom of the chimney.

6. waste gas
clean gas
The dust and ash are charged by the wire kept at a high voltage.
The dust and ash are repelled by the wire to the neutral metal plate.

7. Electrostatic spraying
Electrostatic spraying is used to paint cars.

8. The droplets adhere strongly to the negatively charged car body.
Positively charged droplets repel each other.

9. Hazards of electrostatics
huge amount of electric charges build up on an object
sparks may be produced
inflammable substances nearby
EXPLOSION

10. The floor is covered with anti-static tiles
Ways to avoid build up of static charges
Modern aircraft
Operating theatre
Inflammable anaesthetic gases are used
Anti-static tyres are used.
The floor is covered with anti-static tiles

11. That’s the end of Section 17.3
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Key Ideas
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