This document discusses electric charge and static electricity. It explains that conductors allow electric current to flow through them while insulators do not. When two insulators are rubbed together, they become oppositely charged due to friction. It also describes how charged objects can attract or repel each other depending on whether their charges are opposite or the same. Some applications of static electricity mentioned include electrostatic paint spraying, inkjet printers, and electrostatic precipitators which remove particles from smoke. The document concludes with safety precautions for dissipating built-up static charges.

1. IGCSE (9-1)
Chapter 9: Electric Charge

2. Conductor or insulator?
The setup shows a simple way to test if an object is a conductor (bulb
lights up) or insulator (doesn’t light).

3. Charging and discharging
• When two insulators are rubbed
against each other, they become
(oppositely) charged. Electrons are
removed from one material (which
becomes positively charged) due to
friction, and stick to the other (which
becomes negatively charged).
• To discharge an insulator, simply touch
it to a conductor (e.g. metal rod)

4. Attraction and Repulsion
Opposites attract, likes repel. Charges with the same sign (+ and + , -
and - ) repel each other, but those with opposite signs (+ and - ) attract.

5. Charging by (electrostatic) induction
When a charged object is held close to an uncharged one, charge of
the opposite sign is induced on the side of the uncharged object
closest to the charged one. Then the two objects attract each other.
A good demonstration of this is the
gold leaf experiment [details in
book]

6. Uses of static elcetricity

7. Electrostatic paint spraying
Any object (no matter how awkwardly shaped) can easily be painted by
giving it a charge and using spray paint of the opposite charge.
Advantages:
• Saves time
• Reduces wastage of paint
• Hard-to-reach spots are covered

8. Inkjet printer
Each drop is charged, and depending on the charges on the plates, it
will be deflected to a particular direction. Changing the (size and signs
of the) charges on the plates allows the drops to be correctly
positioned on the paper.

10. Electrostatic precipitator
• The mesh of wires has a high negative voltage across them
• When the ash and dust particles pass through them, they also
become negatively charged
• These negatively charged particles
then stick to the earthed plates, so
are removed from the smoke
(reducing environmental pollution)

11. Risks and Precautions
Dangers with static electricity: Large fuel tankers and airplanes can
become charged after a journey (due to frictive rubbing with the air).
If you then carelessly touch the vehicle, you’ll receive a shock. Worse, if
the vehicle is refueled before removing this built-up charge, a spark
will result, which might cause the fuel to ignite/explode.
Solution: So in these situations, the object must be earthed first (using
thick metal cable connected to the ground). This causes the static
charge to (flow to ground and) dissipate.

12. That’s all you need to know!
THE END