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  1. A review on electric circuits so far.
  2. What is current?
  3. How are currents affected by series and parallel configurations?
  4. What does "conventional current" mean?
  5. What is the Junction Rule?
  1. Understanding Kirchhoff's Junction Rule by using the Water (River Current) Analogy
    Find the volume of water passing through each point (A, C, and D).

    Introduction to Waves
    1. Finding Current in Series Only Circuit vs. Parallel Only Circuit
      1. Find the current through each resistor in series.

      2. Find the current through the missing resistor (R2) in parallel.

    2. Finding Current in Circuits with BOTH Series & Parallel Configurations
      Find the electric current going through each resistor.

      Topic Notes

      In this lesson, we will learn:

      • A review on what is an electric circuit and the main components: battery (voltage), closed wire path (current), and devices/resistors that use up electricity (resistance).
      • What is current?
      • What is the difference between connecting your circuit in series vs. parallel configurations for resistors?
      • What is electron flow/ electron current? How is it different from conventional current?
      • Kirchhoffs 1st Rule: Junction Rule for solving current questions
      • How to solve current problems for both series and parallel circuits by using the concepts of: (a) thinking of electric current as river water current and (b) Kirchhoffs 1st Rule (Junction Rule) for solving current problems


      • The electric current is the rate that electric charge is flowing through the circuit
        • Electric current can be considered as a type of electricity
        • Electricity is the energy from charged particles that can be either dynamic (moving) or static (not moving and accumulating in one place)
      • The unit for current is the ampere (A), and can be measured with an ammeter connected in series
      • In terms of current, the advantage of a parallel configuration is that the circuit will not fail as easily; even if one part of the circuit is faulty, the current can still flow through other pathways to make its way around a complete, closed circuit loop.
        • In a series configuration, if one part is faulty, the whole circuit becomes faulty.
      • In reality, the conventional current (rate of flow of positive charge from positive to negative battery terminal) is NOT what happens
        • The real carrier of charge is the electron, which has negative charge.
        • The rate of flow of negative charge is called electron flow or electron current, and it flows in the opposite direction to conventional current (from negative to positive battery terminal)
        • Recall electrostatics: like charges repel, opposite charges attract. For conventional current, protons are being repelled away from the positive terminal and move toward the attracting negative terminal; for electron current, electrons are being repelled away from the negative terminal and move toward the attracting positive terminal
      • Kirchhoffs 1st Rule, also known as the Junction Rule, states that the sum of currents entering a junction is equal to the sum of currents leaving that junction
        • Iin=IoutI_{in} = I_{out}
        • The flow of electric charge within the circuit is conserved
        • A junction is where the path of electric flow either splits or converges.
      • We will use the water (river current) analogy for electric current
        • The same volume of water will stay within the pipes (current within wires of circuit)
        • The water can split and come back together (junction rule; the amount entering the split is the same as the amount leaving the split)