Electricity and Magnetism Review

• Static Electricity
  •  elementary charge
    • understanding at atomic level
  • fundamental laws or electric attraction and repulsion
  • electroscope
  • charging
    • by friction
    • by contact (conduction)
    • by induction
• Electric Current
  •  1 Coulomb = 6.24 x 10¹⁸ e
  • e = 1.6x10^-19 Coulombs (elementary charge is +ve)
  • Q=Ne , [ Coulombs=number of elementary charges x the elementary charge
  • Current I=Q/t, [Amperes=Coulombs/seconds]
• Electrical Potential
  • terminology - Electrical Potential (symbol V) also called Electrical Potential Difference (but not to be confused with Electrical Potential Energy) has the units Volt (symbol V) (the term Voltage is a commonly used misnomer for Electrical Potential Difference)
  • from the view point of static electricity, compare to Gravitational Potential Energy / mass - i.e. mgh/m
    • V=W/Q, [Volts=Joules/Coulombs]
  • from the viewpoint of current electricity can be compared to water pressure
• Kirchoff's Laws
  • Laws we should appreciate
    • Kirchoff's law of conservation of energy
    • Kirchoff's law of conservation of charge
  • The laws we really need to know and understand
    • Kirchoff's Voltage Law (KVL)
    • Kirchoff's Current Law (KCL)
• Ohms Law
  • complete circuit
    • comparison to water circuit

    • Electrical Circuit	Water Circuit
      Potential Difference (Voltage)	Pressure
      Electrical Current	Flow Rate
      Electrical Resistance	Restriction

  •  V=IR [Volts=Amperes x Ohms)
  • Equivalent resistors and circuit analysis
    • Series R_T=R₁+R₂+...+R_N
    • Parallel 1/R_T=1/R₁+1/R₂+.....+1/R_N
  • Circuit Analysis
• Power
  •  P=VI, [Watts=Volts x Amperes]
    • P=I²R, [Watts=Amperes² x Ohms}
    • P=V²/R [Watts=Volts²/Ohms]
• Cost
  • We purchase energy not power. Units are unusual for SI but make sense to have reasonable size numbers for accounting.
  • E=Pt, [Kilowatt hours=Kilowatts x hours]
• Magnetic Fields
  • have a direction from N to S
  • are actually in 3-space
  • magnetic lines diagrams
  • domain theory
  • magnetic field around a straight conductor
  • magnetic field in a solenoid
  • motor principle
  • Right Hand Rules

    • 		Fingers	Thumb	Palm
      1	Wire	Magnetic Field	Current Flow
      2	Solenoid	Current Flow	North
      3	Motor	Magnetic Field	Current Flow	Force

    • also Left Hand Rules (substitute left hand for left hand and electron flow for current flow)