Current - Electric Circuits

Current

Lessons

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?
  • Kirchhoff’s 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) Kirchhoff’s 11st Rule (Junction Rule) for solving current problems

Notes:

  • 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
  • Kirchhoff’s 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)
  • Intro Lesson
  • 2.
    Finding Current in Series Only Circuit vs. Parallel Only Circuit
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Current

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