Creating Static Electricity

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Creating Static Electricity
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Electrical Insulators

• Conductivity is the ability of materials to allow
  electrons to move freely in them
• Materials that hold onto their electrons and do
  not allow them to move easily are called
  electrical insulators
• ex) Dry wood, glass, and plastic are all examples
  of electrical insulators
• An insulator can hold a static charge because
  static charges remain nearly fixed in place.

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Electrical Conductors

• An electrical conductor is a solid, liquid, or
  gas that allows the movement of electrons
• ex) silver, aluminum, iron, moist skin, salt
  water, water vapor
• A conductor cant hold a static charge because it
  allows the charges to flow through it

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Conductors and Insulators

• Since electrons cannot move through an insulator
  they can be very useful to us to protect us from
  shocks
• A simple electric kettle would be very hazardous
  if the two wires that supplied electricity to it
  did not have a rubber coating over them

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Why do we get more shocks in the winter than in
summer?

• This is because in winter the air is far dryer
  than in the summer and dry air is an insulator
  and therefore does not take any of the charges
  our body might pick up during the day. So when
  we go and touch another conductor (a door handle)
  ZAP we receive a shock

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Charging by Friction

• When two objects made of different materials rub
  together, electrons can be transferred from one
  object to the other
• This is because different atoms (which make up
  the objects) have a different ability to attract
  electrons and a different ability to hold onto
  their own electrons.

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Electrostatic Series
acetate Weak hold on electrons             Strong hold on electrons
glass Weak hold on electrons             Strong hold on electrons
wool Weak hold on electrons             Strong hold on electrons
fur, hair Weak hold on electrons             Strong hold on electrons
calcium, magnesium, lead Weak hold on electrons             Strong hold on electrons
silk Weak hold on electrons             Strong hold on electrons
aluminum, zinc Weak hold on electrons             Strong hold on electrons
cotton Weak hold on electrons             Strong hold on electrons
paraffin wax Weak hold on electrons             Strong hold on electrons
ebonite Weak hold on electrons             Strong hold on electrons
polyethelene (plastic) Weak hold on electrons             Strong hold on electrons
carbon, copper, nickel Weak hold on electrons             Strong hold on electrons
rubber Weak hold on electrons             Strong hold on electrons
sulphur Weak hold on electrons             Strong hold on electrons
platinum, gold Weak hold on electrons             Strong hold on electrons
More likely to gain electrons
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Electrostatic Series

• To determine what charges will form, compare the
  location on the table of the two objects.  The
  object that is higher on the table will lose
  electrons and become positive
• ex) when cotton and human hair rub what charge
  will form on each object? Cotton is lower on the
  list than hair
• Cotton will hold its electrons better. Hair will
  lose its electrons to the cotton and become
  positive. Cotton will become negative.

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Electrostatic Series

• Consider the following pairs are rubbed together.
  Give charge on each
• Plastic ________ Silk _______
• Fur __________ Rubber
• glass ____ silk ______
• Vinyl ______ Plastic ______
• Ebonite _________ wool _____________

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Charging by Induction

• Charging by induction means charging without
  direct contact
• When a negative charge approaches a neutral
  object, the electrons inside the neutral object
  are repelled.  This causes an induced positive
  charge on the side closest to the negative object
  and an induced negative charge on the opposite
  side.
• When a positive charge approaches a neutral
  object, the electrons inside the neutral object
  are attracted.  This causes an induced negative
  charge on the side closest to the positive object
  and induced positive charge on the opposite side.

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Charging by Induction
Induction is used in photocopiers, lightning,
dust filters and electrostatic painting.
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Charging by Contact

• Negative charges (or electrons) will always move
  from where there are the greatest number to where
  there are the fewest
• If there is a big enough difference and the two
  objects are close enough together, this jumping
  may cause a spark
• When do we see the greatest spark - when the air
  is dry or when there is high humidity ? When the
  air is dry because dry air is an insulator

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Charging by Contact

• When transferring by contact, negative charges
  move from one object to the object being touched
• Remember! Only the negative charges move!

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Charging by Contact

• Sparks produced by a charge transferred by
  contact can be dangerous
• Transferring a charge by friction is difficult
  to avoid when charging by contact occurs, one
  object is already electrically charged
• The other object may or may not be charged, the
  important factor is that there is a DIFFERENCE in
  the charge on the two objects

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Grounding

• The earth is large and absorbs large numbers of
  electrons, ground wire is connected to earth to
  "dilute" the charge by carrying it to the earth

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Static Electricity can be Dangerous

• With any phenomena, one of the first things
  people think of is whether or not it is dangerous
  to them. Static electricity can be dangerous in
  certain situations.
• Lightning
• Lightning during a thunderstorm is very high
  voltage, high power static electricity. Getting
  struck by lightning is extremely dangerous and
  kills several people each year. Therefore, you
  should be careful about standing in an open field
  and near metal poles or trees during a
  thunderstorm, in order to avoid getting zapped.
• The record for being struck by lightning and not
  being killed is held by a U.S. Forest Ranger. He
  has been struck by lightning 9 different times!

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Dangerous Static Electricity

• Sparks and computers
• When you walk across a rug and then touch
  someone, you can often cause a spark to fly. This
  can be irritating, especially if you touch
  someone on the nose, but it is not necessarily
  dangerous
• On the other hand, if you happen to touch a
  computer circuit board, the spark even a very
  small one can severely damage the circuitry.
  The sudden surge of electrons can easily fry
  microchips in the computer. That is why
  technicians who work on computers are very
  careful to avoid build-up of static electricity

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Dangerous Static Electricity

• Explosions
• When a gasoline truck fills the underground tanks
  at a filling station, they are very careful about
  any buildup of static electricity caused by the
  flowing liquid into the tank. A static electrical
  spark could cause an explosion of the gasoline.
  Special precautions are made through the use of
  grounding cables to prevent any sparks
• Another area of concern about static electricity
  is in grain elevators and storage bins. When they
  pour the wheat or grain into the bin, the air
  gets filled with a lot of very fine dust. Any
  spark caused by static electricity can cause the
  dust to ignite and explode.