HOW OBJECTS BECOME ELECTRICALLY CHARGED

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HOW OBJECTS BECOME ELECTRICALLY CHARGED
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WHAT DO WE KNOW SO FAR?

• THREE MAIN WAYS IN WHICH OBJECTS BECOME
  ELECTRICALLY CHARGED
• (1) BY FRICTION (rubbing)
• (2) BY CONTACT (touching)
• (3) BY INDUCTION (no direct contact)

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CHARGING BY FRICTION

• Is the transferring of an electric charge from
  one substance to another by rubbing.
• EX combing your hair, petting your cat,
  rods/fur, feet on the carpet

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CHARGING BY FRICTION
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ELECTROSTATIC SERIES

• An ordered list of materials that help us to
  understand the ways in which electrons are
  transferred from one material to another.
• Example When you rub an EBONITE rod with a
  piece of FUR the electrons move from the fur to
  the rod and the rod becomes electrically charged
  (positively).

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CHARGING BY FRICTION QUESTIONS

• What is the charge on a plastic comb or a wool
  sweater under normal circumstances?
• When a wool sweater rubs against a plastic comb
  what happens?
• What is the law of electric charges?
• How can you determine if an object is charged? If
  it is charged, how can you tell is the charge is
  positive or negative?

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CHARGING BY FRICTION QUESTIONS

• 5) You have 2 objects one object has a negative
  charge and repels the second object. What is the
  charge of the second object?
• 6) You have 2 objects one object has a negative
  charge and attracts the second object. What is
  the charge of the second object?
• 7) What way is plastic food wrap charged when it
  is smoothed onto a bowl?

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CHARGING BY CONTACT

• ELECTRIC CHARGE TRANSFERRED FROM ONE SUBSTANCE TO
  ANOTHER BY ACTUAL CONTACT.
• IMPORTANT FACTOR ? ONE OBJECT MUST BE
  ELECTRICALLY CHARGED OTHER OBJECT MAY/MAY NOT
  BE CHARGED.

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• ANOTHER IMPORTANT DIFFERENCE
• - DIFFERENCE IN AMOUNT OF CHARGE ON TWO OBJECTS
  MUST EXIST.
• EX TOUCHING A DOORKNOB

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EXAMPLE SITUATION

• As you get ready to reach out and touch a
  doorknob, it is possible that you are negatively
  charged due to FRICTION with the carpet.
• When you actually touch the knob, some of the
  electrons are transferred from you to the knob
  and you now share the negative charged between
  you.
• The shock produced can be surprising and even
  painful. This is because the charges are shared
  very rapidly (even before the touch happens) and
  thus will produce a mini lightning stroke.

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HOMEWORK QUESTIONS

• Questions 1, 2, 3, 4, and 7 on page 279.

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CHARGING BY CONTACT
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CHARGING BY INDUCTION

• INDUCTION
• - SOMETHING IS MADE TO HAPPEN WITHOUT DIRECT
  CONTACT.

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CHARGING BY INDUCTION
BEFORE
AFTER
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INDUCED CHARGE SEPARATION

• DUST PARTICLE (UNCHARGED OBJECT) ON TELEVISION
  SCREEN OR COMPUTER MONITOR BECOMES CHARGED BY
  SIMPLY BEING ON THE SCREEN.

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• WHETHER AN OBJECT IS CHARGED POSITIVELY OR
  NEGATIVELY, THE DUST PARTICLE IS STILL ATTRACTED
  TO IT.

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• WHAT WOULD YOUR LIFE BE LIKE IF YOU WERE NO LONGR
  ABLE TO WATCH TELEVISION, LISTEN TO THE RADIO, OR
  TALK ON A CELL PHONE ?

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CHARGING CONDUCTORS BY INDUCTION

• COMMON DEVICES INCLUDE MICROPHONES, TELEVISION
  CAR RADIO AERIALS, CELL PHONES, LIGHTNING RODS.

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STATIC ELECTRICITY ADVANTAGES

• POLLUTION DUST CONTROL
• AIR CLEANERS IN HOMES HOSPITALS REMOVE DUST
  PARTICLES BY USING THE ATTRACTION BETWEEN UNLIKE
  CHARGES.
• POSITIVELY CHARGED DUST PARTICLES ARE FORCED
  BETWEEN NEGATIVELY CHARGED FLAT PLATES.

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• COATING SURFACES WITH PARTICLES
• MACHINE-PAINTING EQUIPMENT
• TINY PAINT PARTICLES FROM A SPRAY GUN ARE CHARGED
  AS THEY PASS AN ELECTRODE ATTACHED TO THE GUN.
• OBJECT TO BE PAINTED IS GIVEN A CHARGE OPPOSITE
  TO THAT OF THE PAINT.
• CHARGED PAINT PARTICLES ARE ATTRACTED TOWARD THE
  OPPOSITELY CHARGED OBJECT.

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STATIC ELECTRICITY VIDEO CLIPS

• STATIC ELECTRICITY
• ELECTROSCOPE
• ELECTROSCOPE EXPERIMENT
• GOLD LEAF ELECTROSCOPE