static electricity
TRANSCRIPT
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Static Electricity
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History• Electron means “amber” in Greek
• Thales of Miletos 600 BC discovered properties by Greek.
• He rubbed amber (mineral) with cat fur and attracted feathers.
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Ben Franklin’s Kite Experiment (1740’s)
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Benjamin Franklin
• 1740’s lightning experiment with kite, key and Leyden jar (stores static electricity).
• Franklin developed the lightning rod.
• Proposed conservation of charge.
• Saw electricity as a flowing fluid and called the flow direction positive.
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Law of Charges
• Like charges repel
• Opposite charges attract
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Law of Conservation of Electrical Charge
• The net charge of an isolated system remains constant.
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Electrical Charge
• Symbol: q
• Unit : Coulomb, C
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Charge and Mass of the Electron
• Charge of Electron:
1.6 x 10-19 C (Coulombs)
• Mass of Electron:
9.11 x 10-31 kg.
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Positively charged
objects lost electrons.
Example: Rubbing a glass rod with silk. • Rod becomes + (loses electrons)• Silk becomes - (gains electrons).
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Negatively charged objects have gained electrons.
Example: rubbing a rubber rod with fur. • Rubber Rod: - charged• Fur: + charged
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Types of Materials in terms of Electrical Conductivity
• Conductors (metals)
• Semiconductors (germanium, silicon)
• Insulators (wood, glass, rubber)
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Electrostatic Charging Methods
• Friction
• Conduction
• Induction
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Charging by Friction
• The two objects wind up with opposite charges.
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Charging by Conduction (direct contact)
• The objects end up with the same type charge.• If the charges are equal in size, they share the charge
equally.
http://www.ap.smu.ca/demonstrations/index.php?option=com_content&view=article&id=106&Itemid=85
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Charging by Induction
• Objects ends up with opposite charge.• Involves grounding.
http://www.physics.sjsu.edu/becker/physics51/elec_charge.htm
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Electroscopes are used to test the charge of an object.
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When a charged object is brought near the electroscope,
its leaves spread apart.
http://upload.wikimedia.org/wikipedia/commons/e/ec/Electroscope_showing_induction.png
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When a charged object touches an electroscope, the
electroscope is now charged.
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What was the charge of the object that touched this
electroscope?
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Polarization
http://www.csiro.au/helix/sciencemail/activities/WaterBend.html
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Part II
• Coulomb’s Law
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Coulomb’s Law
• 1785,Charles Augustin Coulomb (French scientist)
F = k q1q2
______
d2
• k = 9 x 109 Nm2/C2
• d (or r): distance between the charges.• q : charge of each object.
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The Direction of the Electrical Force
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Coulomb’s Law is an Inverse Square Law
http://web.ncf.ca/ch865/graphics/Coulomb.jpeg