Electrostatics

• What does the electro prefix mean in electrostatics?

  Electric charge
• What does the statics suffix mean in electrostatics?

  Non-flowing
• What are the sources of charge?

  Electrons and Protons (opposite but equal amount of charging).
• What makes a neutral object?

  Balanced amount of protons and electrons.
• What is the unit of charge?

  Coulomb (C)
• What is an elementary charge?

  The charge of one proton or one electron.
• How much charge is an elementary charge?

  1.6 x 10^-19 C
• How much is a micro charge?

  µ= =10^-6
• How much is a nano charge?

  n= 10^-9
• Conductors


  materials that exchange charge easily
• Conductor Examples


  Metals (Copper, Gold, Silver,etc)
• Insulators

  materials that do NOT exchange charge easily
• Insulator Examples 


  Plastic, Rubber, Wood, Glass
• What are the two types of materials?

  Conductors and Insulators
• Electric Force (Fe)


  exerted between all charged objects
• What determines the direction of electric force?

  Opposite charges attract. Like charges (Positive and Positive, or Negative and Negative) repel each other.
• What determines the magnitude of electric force?

  Coulomb's law (Fe= (k)(q1q2/r^2)
• What number is k in the Coulomb's Law Equation?

  9x10^9 Nm^2/C^2
• What are the three methods of charging?

  Triboelectric, Conduction, Induction
• Triboelectric 


  Charging by friction; exchange of electrons via rubbing
• Triboelectric Examples


  rubbing a balloon in your hair, socks on the carpet.
• Conduction


  Exchange of electrons between conductor objects via contact. Charge is exchanged until equilibrium/balance is reached.
• Conduction Example


  A positively charged aluminum plate is touched to a neutral metal sphere. The neutral metal sphere becomes charged as the result of being contacted by the charged aluminum plate.
• Induction 


  indirect method of charging that uses an induced charge and a ground to change a neutral object.
• What is polarization? 


  the process of separating opposite charges with an object. Positive charges become separated by negative charges. By inducing the movement of electrons within an object, one side is left with an excess of positive charge and the other side is left with an excess of negative charge.
• Polarization Example

  Rubbing a balloon on your head and then sticking it to the ceiling causes the balloon to stick to the ceiling.
• What is a ground?

  A conductive path to earth. Removing the ground traps the charges on earth.
• What does the q in the Coulombs law equation mean?

  q=charge in object(Units:C)
• What does r mean in Coulomb's law equation?

  r= the separation between charges distance. (Units: meters(m))
• What if there are more than 2 forces?

  -Draw a Free Body Diagram and use Coulomb's law to determine individual forces.

  • Can determine net force if needed
• If an object is neutral, what can you say about the amounts of positive and negative charge it contains?

  They are equal. There is a balanced number of protons and electrons.
• Is the total amount of charge in the universe changed when we charge an object?

  No, the total amount of electric charge in the universe is constant.
• A system consists of two charges separated by 1m. How does the magnitude of the electric force change when each charge and the separation distance are doubled?

  The magnitude of the force stays the same. The effects of doubling the charge and distance cancel.
• What is the direction of the electric force between two positive charges?

  A repulsive force acts along the line connecting the two charges.
• Electric Field

  • Electric force occurs without contact
  • Interaction is carried out via a field
  • Field force (similar to gravity)
  • Field is a property of space due to the presence of charge(s)
  • Vector quantity
  • The electric field is defined based on the electric force experienced by a positive test charge, qo.
• What is the direction of electric fields?

  Same as direction Fe on qo

  • Positive Charges: Points away from center
  • Negative Charges: Points towards the center
• How do you find the magnitude of an electric field?

  E=Fe/qo or E= k(q/r^2). (E units: N/C)
• What are drawings of electric field lines?


  Continuous lines that show the direction and relative strength of the field.
• Rules of drawing electric field lines

  • Lines start on positive charges, or at infinity
  • Lines end on negative charges, or at infinity
  • Number of lines that begin or end the charge is proportional to the amount of charge.
  • Line NEVER cross
• Single charge electric field diagram

  -2c to -4c

  A) more