Chapter 19: Electric Charges and Currents

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Chapter 19 Electric Charges and Currents

• 19-1 Electric Charge
• 19-2 Static Electricity

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Electric Charge

• All matter is made up of atoms, and atoms are
  made up of tiny particles called protons,
  neutrons, and electrons.
• Both protons and electrons have a basic property
  called charge - protons are positive and
  electrons are negative.

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Charge and Force

• A force of attraction pulls objects together -
  this exists between 2 oppositely charged
  particles
• (negative-positive)
• A force of repulsion pushes objects apart - this
  exists between 2 like charges
• (neg-neg, pos-pos)

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Rule for Charges

• Like charges repel each other, unlike charges
  attract each other

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Electric Field

• Definition the arrangement of field lines that
  determine the force per unit charge a small
  stationary charge would experience at each point
  in space
• The pattern of an electric field depends on the
  number, size, sign, and location of charges.
• The electric field is visualized by showing lines
  of force
• Force is stronger where lines are closer together
  - occurs when charges are close
• The direction of the force depends on whether the
  placed charge is positive or negative

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Electric Field - Like Charges
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Electric Field - Unlike Charges
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Electric Field - Charges
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19-2 Static Electricity

• Electrons may be loosely held to their atoms - so
  they can easily be separated from their atoms.
• An entire object can acquire a charge
• A neutral object acquires an electric charge when
  it either gains or loses electrons.

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Methods of Gaining or Losing Charges

• Friction removes the charges from an object and
  places them on another object.

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Methods of Gaining or Losing Charges

• Conduction electrons flow through one object to
  another by direct contact.

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Methods of Gaining or Losing Charges

• Induction charges are rearranged and line up in
  different positions.

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Conductors and Insulators

• Conductors material which permits electrons to
  flow freely or transfers heat more easily than
  other substances. Ex metals silver,
  copper, aluminum
• Insulators material made up of atoms with
  tightly bound electrons that are unable to flow
  freely do not conduct electric charges well.
  Ex rubber, glass,
  wood, plastic, dry air
• Polarized partial alignment of negative and
  positive charges in molecules in response to an
  electric field

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Electric Discharge

• Transfer of electrons from one object to another
  results in a static charge on each object.
• Static electricity is the build up of unbalanced
  electric charges on an object
• Electrons that move from one object to another
  eventually leave the object
• Electric discharge loss of static electricity as
  electric charges move off an object

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Lightning

• Charges separate within the thunderclouds
• There is a build up positive and negative charges
  in different parts of the cloud
• Objects on Earth become electrically charged by
  induction
• Charges move away from the cloud, positive
  charges are left closest to ground transfer of
  electrons is lightning
• Lightning can be cloud to cloud
• Thunder is the expansion of air from the heat
  produced by lightning

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Lightning Rods and Grounding

• Benjamin Franklin lightning rods
• Grounding the Earth is extremely large and is a
  good conductor of electric charge. Earth can
  easily accept or give up electric charges.
• Lightning rod is put on top of buildings. A wire
  is run from the rod to the ground where lightning
  can pass through safely. The charge then goes
  into Earth.

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Lightning Rods and Grounding
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Electroscope

• Can detect electric charges
• Consists of 2 leaves, a metal knob, and a metal
  rod
• A charge is put onto the knob which then flows
  down the metal rod into the leaves separating
  them.
• If an electroscope is touched by a negative
  charge, the negative charge flows down the rod
  into the leaves, giving both leaves a negative
  charge and causing them to separate (like charges
  repel). Same thing will happen if a positive
  charge is put to the electroscope.