UNIT A: ELECTROSTATICS AP Physics C Review 1. Electric forces and charges The electric force is one...
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Transcript of UNIT A: ELECTROSTATICS AP Physics C Review 1. Electric forces and charges The electric force is one...
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UNIT A: ELECTROSTATICSAP Physics C Review
Electric forces and charges
• The electric force is one of four fundamental forces.
• The electric force is the result of electric charges.
• There are two kinds of electric charges.
• Electric charge is conserved.
• Electric charge is quantized.– The charge on an
electron is -1.60 x 10-19 C.
Methods of Charging an Object
• Conductors and insulators can be charged by contact.
• Conductors can be charged by induction.
• A charge can induce a surface charge in insulators by polarization.
Charging by Induction
©2008 by W.H. Freeman and Company
4
Clarification: The conductor never touches the charged plate.
© 2009 Richard White, LearnAPphysics.com
Coulomb’s Law
• The electric force one charge exerts on another is given by Coulomb’s Law
• A negative force means attraction, positive means repulsion.
• kC = 8.99 x 109 Nm2/C2
• Coulomb’s constant is sometimes written
21electric rF ,221 ˆ
r
qqkC
04
1
Ck
6
Superposition
• Superposition- the force on a charge due to several other charges is the vector sum of the forces from the other charges.
©2008 by W.H. Freeman and Company
7© 2009 Richard White, LearnAPPhysics.com
8
Electric Field
• The presence of charges causes electric fields. The electric field at a location is the force / Coulomb of charge felt by a positive test charge at that location.
• The electric field caused by a point charge is
• Electric fields are measure in Newtons/Coulomb (or Volts/meter).
• The principle of superposition applies to fields as well.
q
FE
2r
qkE C
itot EE
9© 2009 Richard White, LearnAPphysics.com
• An electric dipole consists of two equal and opposite charges that are a small distance apart.
• Far away from the dipole, the E field is
iE ˆ43x
kqa
Electric Field of a Dipole
©2008 by W.H. Freeman and Company
Electric Field Lines
– Electric fields can be represented using electric field lines.
• Lines begin on positive charges (or infinity) and end at negative charges (or infinity).
• Lines enter or leave an isolated charge symmetrically.
• The magnitude of the field is shown by the number of lines in a given area.
• The number of lines entering or leaving a charge is proportional to the magnitude of the charge.
• At a large distance, every arrangement of charges approximates a point charge.
• Lines do not cross.
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12© 2009 Richard White, LearnAPphysics.com
13© 2009 Richard White, LearnAPphysics.com
©2008 by W.H. Freeman and Company