Static Electricity

1
Static Electricity

• Define some of the major ideas about static
  electricity

2
Static Electricity

• Electricity exists because of two types of
  charge
• Charge is () or (-)
• Fundamental unit is the charge of one electron
  one proton 1.6 x 10-19C
• Unit of charge is the Coulomb. One coulomb is a
  boatload of electrons
• Like charges repel, opposites attract
• Charge is Quantized, you cant have ½ of an
  electron charge. Cant break the charge on one
  electron any smaller.

3
Static Electricity

• Ways to charge objects include
• Friction, like rubbing the fur on plastic
• Conduction, touching a charged object to another
  object
• Induction, like in the lab (which maybe didnt
  work too well). Bring a charged object next to a
  conductor and then ground the conductor,
  leaving it charged.

4
Static Electricity

• Insulators electrons are held tightly and cant
  move around easily, so electricity doesnt move
  through them. Examples are rubber, plastic, glass
• Conductors charge (electrons) moves easily.
  Examples are metals copper, aluminum, gold

5
Static Electricity

• Electric Force
• You saw the tape attract or repel, what causes
  things to move? (rhymes with horse)
• There is an electric force between any 2 charged
  objects called the Coulomb Force
• Force depends on the amount of charge on each
  object and on the distance between them. This
  force is analogous to the Universal Gravitational
  Force. Can you write the equation for these?

6
Electric Force

• Coulombs law for electric force
• F (kq1q2)/r2
• q amount of charge in coulombs
• r distance between charged objects
• k Coulomb constant 9x109
• The force is the same on both charged objects
  (remember forces exist in pairs, Newtons 3rd law)

7
Electric Force

• The electric force is conceptually much bigger
  than the gravitational force.
• Why dont we see the electric force much?
• Objects in our world are typically neutral (even
  number of electrons and protons)

8
Electric Field

• Much like the concept of an invisible
  Gravitational Field, there exists an invisible
  electric field around any charged object.
• The Electric field is defined as the Force that
  another charged object (test charge) would feel
  in the presence of the source charged object
  divided by the amount of the charge on the test
  charge
• E F/q kQq/r2q kQ/r2

9
Electric Field Lines

• Electric field lines surround a charged object
  and point in the direction that a positive ()
  test charge would be forced to move