Electric Charge

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Electric Charge

• Section 7.1

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Static Electricity

• All matter made up of atoms which contain ()
  protons and (-) electrons
• Usually the number of protons number of
  electrons
• Some atoms hold onto their electrons better than
  others

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What happens when I walk on Carpet?

• The electrons from the carpet are loosely held
  and get stuck on your shoes.
• This buildup of electrical charge is called
  static electricity

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Conservation of Charge

• Law of conservation of charge charge can be
  transferred but cannot be created or destroyed

• During any process, the net electric charge of an
  isolated system remains constant (is conserved).

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Opposites Attract

• Charged object obey two rules
• Opposites attract
• Like charges repel

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Electrical Force at a Distance

• Charges can act at great distances and exert an
  electrical field
• This field can move the charges around an object
  brought near it
• Any charge placed in an electric field will be
  pushed or pulled by the field

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Conductors and Insulators

• Conductors materials that allow electrons to
  move through them or readily conduct electric
  charge.
• Metals (such as copper, aluminum, silver, and
  gold) and skin
• Insulators materials that block the flow of
  electrons through them
• Plastic, wood, air, rubber, glass

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Transferring Electric Charge 3 ways

• 1. Charging by contact (Conduction)
• Some materials when rubbed together will become
  charged
• The electrons of one of the objects moves to the
  other object
• Example feet rubbing the carpet

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Charging an Object
Ebonite rod Fur ? Negatively charged ebonite
rod Glass rod Silk ? Positively charged
glass rod
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2. Charging by induction

• Because of electrical fields -if a charged object
  is brought near a neutral object, it can induce a
  charge on the neutral object.

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Detecting Electrical Charge

• Electroscope a device that detects electrical
  charge on an object

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Charged object brought near neutral object
Negative charge of balloon pushes electrons away
causing a positive charge to be induced on the
surface
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3. Static Discharge

• A transfer of charge through the
• air between two objects
• The buildup of a
• static electricity causes a spark!
• Example lightning

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Lightning

• Swirling clouds and air
• currents cause a buildup of
• static charge in the clouds
• When the buildup becomes
• great enough a positive charge
• is induced on the Earth
• Buildup is so great --the electrons travel from
  cloud into the Earth to neutralize the
  oppositely charged areas

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Types of lightning ?
Cloud to groundNOAA Central Library
Ground to cloudpicture from NASA
Cloud to cloudNOAA Central Library
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Grounding

• Grounding providing a path that allows
  electrical charges to travel directly into the
  Earth rather than traveling through a building