Lightning is a very LARGE electrical discharge that is caused by INDUCTION!

Charges build up in storm clouds and they need a place to escape.

The path of escape is for these charges to discharge to Earth.

In a thunderstorm, a negatively charged area builds up at the base of the cloud.

This negative area at the base of the cloud creates a positive area that builds up on the ground▪ This is caused due to induction – think of the pen

picking up the paper because its electrons move away from the negative pen.

When enough charge builds up, the cloud discharges its excess electrons to the ground – this creates a huge spark: lightning!

Figure 10.22

Video: Lightning http://www.youtube.com/watch?v=Q3Awp-3CxSU

Lightning: is the spark that we see as the excess electrons in a storm cloud discharge to the ground.

Thunder: is the sound of the rapid expansion of air that occurs when this spark moves from the cloud to the ground.

Lightning Hitting a Tree

Practical Uses of Electrostatics

1. Lightning Rods2. Electrostatic Spray

Painting3. Photocopiers4. Electrostatic Precipitator5. Static Charge at Home

Lightning rods are metal rods that are placed near or on a building to attract lightning and conduct it safely to the ground.

They become charged (+) by induction and then provide a path for the lightning.

1. Lightning Rods

2. Electrostatic Spray Painting

Special type of spray painting that involves charging the object to be painted with a positive (+) charge

The paint coming out of the paint gun has a negative charge

This allows the paint to coat the object with a very smooth finish Used in industrial painting Most often the auto-industry

3. Photocopiers

The page to be copied is reflected on a positively (+) charged selenium coated drum

The metalloid selenium is a conductor in the light and an insulator in the dark.

Where the print is reflected becomes charged while the rest of the paper is uncharged.

The negatively charged toner is brushed across the page and sticks to the positive charges!

See PAGE 422 in text

4. Electrostatic Precipitator A charged conductor in the center of a

chimney stack charges particles in the smoke

These particles are then attracted to the grounded outside wall of the chimney where the charge is lost and the particles are deposited and so they do not escape into the air.

Some home furnaces have electrostatic filters.

Electrostatic Precipitator

5. Static Charge at Home

In the dryer: Different materials build up static charges and this causes them to stick together!▪ Dryer sheets can stop this because they add a layer

of waxy chemicals to clothing that creates less friction between clothes (less static).

Walking in socks on the carpet: Lots of friction gives you a charge. If you touch a metal doorknob you will get a shock.

Putting a sweater over your head: Hair gets a static charge.

Plastic Wrap: Charged plastic that clings to a neutral bowl.

Grounding Static Charges on Vehicles

Cars and planes may build up charges on their surface through friction between the vehicles outer surface and the air.

A simple way to prevent static build up is by using: a ground strap for cars a needle-like projection on an airplane that

disperses charges into the air See PAGE 419 pictures in your TEXT

Static Charges and Flammable Materials Sparks from the build up of static charge can be very dangerous if you are around flammable

materials. When planes/cars are fuelled, the very

explosive fuel moving through the nozzle creates a build up of static charges.

If the nozzle comes too close to the plane’s body, a spark could ignite the fuel!

To prevent this, when fuelling, both the plane and the fuel source need to be grounded.

Homework:

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