Transcript Controlling Static Electricity

Controlling Static
Electricity
What Causes Lightning?
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What we know…Strong winds inside clouds
cause collisions between water droplets and
ice particles
These collision strip electrons from some
particles and deposit them on others
Strong updrafts in the clouds carry smaller
particles up while heavier ones drift down
Negative charges collect at the bottom of the
cloud where the temp is above -20
The higher, colder parts are positively
charged
Lightning …Part 2…
 Negative
charges on the bottom of the cloud
repel electrons on the surface of the earth
 The ground now has mostly positive charge
 Now it works just like any spark
 The strong attraction between the cloud and
ground pull electrons off atoms in the air
 This creates a pathway of ions for the spark to
travel on.
 This normally occurs on a high point - why do
you suppose that might be?
Digging a tunnel
through the air
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The electric field becomes very strong (tens
of thousands of volts per inch),
The air to begin breaking down.
The electric field causes the surrounding air
to become separated into positive ions and
electrons; the air is ionized.
The electrons and positive ions are farther
apart than they were in their original
structure.
Essentially, the electrons have been stripped
from the molecular structure of the nonionized air.
 What
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about that noise we hear?
Many electrons crash though the air at very a
high speed - this causes intense heat as well
as light
 Temperature of the air in and near lightning
can reach 33,000ºC - several times hotter
than the surface of the sun
 This heat causes the air to expand rapidly
 Air molecules colliding with other air
molecules produce a shockwave we know of
as thunder.
What does lightning do?
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Lightning strikes can kill people, knock out radio
communications, electrical power, destroy houses or trees.
 When a person is struck by lightning the chances are about
50% that it will be fatal.
 Usually, the lightning enters the head or one of the ears.
 lightning usually strikes out of the body skin again after a few
centimeters,
 a person usually suffers cardiac arrest, apart from burns,
temporary blindness and deafness.
 In many cases neurons are permanently damaged.
 When a tree is struck by lightning the liquids inside the trunk
and branches turn to gas instantly, leading to high pressure and
literally an explosion of anything that is between the gas and
the open air.
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Usually, the lightning current runs just underneath the
bark, down to ground, and the tree is scarred by a
strip of blown-away bark.
Sometimes, the current may run down near the
center of the trunk. There may be little left of the
tree afterwards.
When a house is hit by lightning, the electrical current
will find its way down by anything conductive,
preferably around the perimeter of the house.
This may include antennas, plumbing and gutters.
Any person taking a bath, making phonecall, washing
hands, or otherwise touching metal plumbing either
directly or indirectly, may be shocked or killed.
Electrical appliances are likely to be damaged or
destroyed, either by large peak currents or by the
electromagnetic shock wave.
Lightning Rods
 We
can’t prevent lightning from striking.
 How can we control damage done by
lightning?
 Direct the flow of electrons away from
the building to prevent fires.
 Where do electrons travel most easily
 Lightning rods are made of metal
conductors
Using Static Electricity
Everyday
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Electrostatics can help us solve problems
 Electrostatic precipitators help to clean the air
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A strongly charged conductor runs up the muddle of the
chimney
 Solids in the smoke get ionized
 They then cling to the sides of the chimney and are scrubbed
off
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Could you design a home air cleaner based on the same
principles?
 Painting
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with Charges
How do new cars get such a smooth coat of
paint?
 The cars are given a positive charge
 The paint is given a negative charge as it leaves
the paint gun.
 The result is a smooth even coat of paint.
More Everyday Electrostatics
 More uses for static electricity
 Separating salt and pepper
 Separating minerals and ores
 Dust mops.
 ….. Can you come up with any more?