Elecs 2: DC Current

• Electrical circuit is a system of conductors though which current of electricity flows upon the application of electrical voltage
• The common conductors in electrical circuits are silver, copper and aluminum.
• There are two general types of electrical current, distinguished from each other by the manner in which they vary in magnitude and direction; these are classified as (1) direct current and (2) alternating current.
• A direct current, sometimes called a

  continuous current, is an electric current that

  flows in one direction
• Direct current can be classified into three

  forms that can be derived from the three

  sources, namely: continuous dc which is

  produced by a battery, unidirectional dc

  derived from a dc generator and pulsating dc

  produced from rectifier circuits (either halfwave

  or full-wave).
• continuous dc which is produced by a battery
• unidirectional dc derived from a dc generator
• pulsating dc produced from rectifier circuits (either halfwave or full-wave)
• An alternating current is one in which the

  direction alternates regularly and, unless

  otherwise definitely stated, changes

  periodically in magnitude as well as direction
• The two types of current flow are the

  conventional flow and the electron flow.
• The conventional flow of current (+ to –

  direction) is still currently the preferred type

  of current flow.
• The electron flow of current which is opposite to the conventional flow is the actual flow of current
• Ohm’s law is the law that relates the three

  basic electrical quantities: current, voltage and resistance
• Ohm's Law was formulated in 1826 by Georg Simon Ohm.
• Ohm's Law: “The current flowing in a circuit is directly proportional to the voltage (applied emf) and inversely proportional to the resistance.”
• power is defined as the time rate at which work is done or the time rate of doing work
• The unit of electrical power is watt (W) named

  after James Watt (1736-1819) where 1 W = 1 J/s =

  1 (V) (A). 1 horsepower (hp) = 746 W.
• The Joule’s law is about power dissipation of a

  resistance element in a circuit
• The Joule’s law is about power dissipation of a

  resistance element in a circuit formulated by James Prescott Joule
• Joule’s law: “Electrical power is dissipated in a

  resistance whenever it carries an

  electrical current. The power

  dissipated is directly proportional

  to the square of electrical current

  and resistance.”
• Series circuit is a circuit in which components

  like resistances are connected end to end so

  that there is only one path for current flow
• Parallel circuit is a circuit in which one end of

  each resistance is joined to a common point

  and the other end of each resistance is joined

  to another common point so that there are as

  many paths for current flow as the number of

  resistances
• This theorem is applicable to series

  circuits where the total source voltage

  is given and voltages across the

  resistances are required

  Voltage Division Theorem
• This theorem is intended for parallel

  circuits where the current flowing in

  each branch is required.

  Current Division Theorem
• Network is the interconnection of components

  such as resistors and batteries forming a

  complicated circuit.
• Branch represents a single element such as a

  voltage source or a resistor
• Node (n) is the point of connection between two

  or more branches.
• Loop is any closed path in a circuit.
• Mesh is a loop which does not contain any other

  loops within it.
• “In any electrical network, the algebraic sum of the currents meeting at a point (or junction) is zero.”

  Kirchhoff’s Current Law (KCL) or Law of

  Conservation of Current
• “The algebraic sum of the products

  of currents and resistances in each

  of the conductors in any closed path

  (or mesh) in a network plus the

  algebraic sum of the emfs in that

  path is zero.”

  Kirchhoff’s Voltage Law (KVL) or the Law of

  Conservation of Voltage
• This method offers the advantage of requiring

  minimum number of equations needed to be

  written to determine desired quantities. This

  method is using the current law alone.

  Nodal Method
• The method involves a set of independent loop currents assigned to as many meshes as existing in the circuit

  Mesh Current
• “the voltage across or current

  through an element in a linear circuit

  is the algebraic sum of the voltages

  across or currents through that

  element due to each independent

  source acting alone”.

  Superposition Theorem
• “Any network with two open

  terminals a and b can be replaced

  by a single voltage source VTH in

  series with a single resistance, Ro.”

  Thevenin‘s Theorem
• “Any network with 2 open terminals a and b can be replaced by a single current source, ISC in parallel with a single resistance, Ro.”

  Norton’s Theorem
• “When any number of voltage sources of arbitrarily generated voltage and finite internal resistance different from zero are connected in parallel,

  the resulting voltage across the parallel combination is the ratio of the algebraic sum of the currents that each source individually delivers when

  short-circuited to the algebraic sum of the internal conductance.”

  Millman’s Theorem
• Also known as Parallel Generator Theorem, this is

  used to compute the voltage at the ends of a circuit made up of only branches in parallel.

  Millman’s Theorem
• “If an emf in a circuit A produces a current in circuit B, then the same emf in circuit B produces the same current in circuit A.”

  Reciprocity Theorem
• “Any resistance R in a branch of a network in which a current I is flowing can be replaced for the purpose of calculation, by a voltage equal to IR.”

  Compensation Theorem