7-8

• RC Circuits


  Circuits that contain both resistance and capacitance

  
• RC Circuits


  • Timing circuits
  • Camera flashes
  • Pacemakers
• Gustav Robert Kirchhoff


  German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy and emission of black-body radiation

  
  

  Formulated two rules in calculating the amount of current

  that goes through a circuit
• Kirchhoff's Rules


  • Kirchhoff's Point/Junction Rule: The sum of all the currents entering a point or junction of the circuit is equal to the sum of all the currents leaving that point or junction
  • Kirchhoff's Loop/Circuit Rule: The algebraic sum of potential charges around any complete loop in the network is equal to zero
• Applying Kirchhoff's Rules

  1. Assign direction of current flow

  2. Label high potential side with + and low potential side with -

  3. Use point rule to get equation I1 + I2 = I3

  4. Consider loop ABCF, use loop rule to get equation V1 - I1R1 - (I1 + I2)R3 = 0

  5. Consider loop DCFE, use loop rule to get equation V2 - I2R2 - (I1 + I2)R3 = 0

  6. Solve the system of linear equations to find I1 and I2

  7. Substitute values to find I3
• Capacitor States


  • Charging: As the e-current enters a capacitor, it stores charges
  • Discharging: As the capacitor releases the stored energy

  o A charging and discharging capacitor each possess different attributes in terms of the current that passes through it, the e-potential across it, and the charge it contains.
• Magnetism


  Recall how there are two kinds of electrical charge (+ and -),

  and likes repel, opposites attract.

  Similarly, there are two kinds of magnetic poles (north and

  south), and like poles repel, opposites attract.

  
  

  Magnetic Poles

  • North-seeking pole and south-seeking pole
  • Like poles repel, opposites attract

  o The repulsion and attraction of the poles are caused by

  magnetic force that exist between the poles.

  o Magnetic poles, however cannot exist in isolation like e-

  charges.

  o Breaking a magnet into two just give you a tiny version of

  the magnet with both N and S poles
• Magnetization and Demagnetization


  • Magnetic properties wear out over time or through techniques like hammering, heating, and exposure to alternating current

  o These techniques involve mixing up the arrangement of

  molecules to cancel the polarity of the entire material

  • Molecules can be re-arranged via magnetization by exposing to another strong magnet
• Magnetic Field


  • A region where another magnetic pole will experience magnetic interaction
  • Graphically represented by magnetic field patterns
  • Density of lines is proportional to field strength

  o North Pole: lines are drawn from it

  o South Pole: lines are drawn towards it
• Charged Particles in a Magnetic Field

  o HANS CHRISTIAN OERSTED: observed that a current

  passing through a conductor deflects a nearby compass in 1820.

  o This gives way to his discovery of electromagnetism.

  o He also discovered that e-current results in magnetism.

  o When charged particles are in motion a magnetic force is formed

  around it; this motion depends on the EMF that made it move

  • Motion depends on the EMF that made them move
  • Greater EMF causes faster movement and greater acceleration
• Cyclotron


  • Apparatus that sets charged particles into motion and subjects them to a magnetic field
  • Particles move outward from center and continuously accelerate
  • Acceleration is directly proportional to radius
  • Cyclotron Frequency: number of revolutions the charge undergoes