Electrical Fundamentals II
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Questions and Answers

What is the concept behind Faraday's law?

  • A change in the magnetic environment of a coil of wire will cause a current to flow in the coil.
  • A change in the magnetic environment of a coil of wire will cause the coil to heat up.
  • A change in the magnetic environment of a coil of wire will cause the coil to move.
  • A change in the magnetic environment of a coil of wire will cause a voltage to be induced in the coil. (correct)

    • What is the term used to describe the voltage generated when a coil is moved into a magnetic field?

  • Magnetic flux
  • Induced current
  • Motional EMF (correct)
  • Electromotive force (EMF)

    • According to Lenz's law, what is the direction of the induced magnetic field?

  • In the opposite direction to the changing magnetic flux (correct)
  • Perpendicular to the changing magnetic flux
  • In the same direction as the changing magnetic flux
  • Parallel to the changing magnetic flux

    • What is the effect of moving a coil into a magnetic field?

    <p>A voltage is induced in the coil</p> Signup and view all the answers

    What is the relationship between the speed of coil movement and the induced voltage?

    <p>The induced voltage is directly proportional to the speed of coil movement</p> Signup and view all the answers

    What is the purpose of the induced magnetic field?

    <p>To keep the magnetic flux constant</p> Signup and view all the answers

    What is the condition for Faraday's law to apply?

    <p>There must be a change in the magnetic environment of the coil</p> Signup and view all the answers

    What is the direction of the current induced in a coil according to Lenz's law?

    <p>In the opposite direction to the changing magnetic flux</p> Signup and view all the answers

    What is the main factor that affects the amount of mutual inductance between two coils?

    <p>The relative positions of the two coils</p> Signup and view all the answers

    What happens to the mutual inductance when the coils are mounted on a common iron core?

    <p>It increases greatly</p> Signup and view all the answers

    Which of the following elements does NOT increase the induced EMF?

    <p>Resistance of the conductor</p> Signup and view all the answers

    What is the purpose of using a ferromagnetic core in a transformer?

    <p>To increase the magnetic field strength</p> Signup and view all the answers

    What happens when the primary current changes in a transformer?

    <p>A voltage is induced in the secondary coil</p> Signup and view all the answers

    What is the relationship between the primary and secondary coils in a transformer?

    <p>The primary coil induces a voltage in the secondary coil</p> Signup and view all the answers

    What is the direction of the induced voltage in the secondary coil?

    <p>Opposite to the primary voltage</p> Signup and view all the answers

    What is the result of increasing the rate of change of flux in a coil?

    <p>The induced EMF increases</p> Signup and view all the answers

    What is the primary function of a PC clock in current computer processors?

    <p>To produce a square wave at a high frequency</p> Signup and view all the answers

    What is the characteristic feature of a sawtooth wave?

    <p>Unequal rise and fall times</p> Signup and view all the answers

    What is the minimum frequency required for a CPU clock to operate at 4.0 GHz?

    <p>4,000,000 clock pulses per second</p> Signup and view all the answers

    How can a triangular wave be generated from a square wave?

    <p>By using an integrator</p> Signup and view all the answers

    What is the main difference between a sawtooth wave and a triangular wave?

    <p>The rise and fall time periods</p> Signup and view all the answers

    Why is a simple switch not suitable for generating a CPU clock?

    <p>It cannot operate at high frequencies</p> Signup and view all the answers

    What happens to the magnetic field around a wire when the current is switched on?

    <p>An expanding magnetic field is produced</p> Signup and view all the answers

    What is the relationship between the induced voltage and the magnetic field?

    <p>The induced voltage is in the opposite direction to the magnetic field</p> Signup and view all the answers

    What happens to the magnetic field when the switch is closed?

    <p>The magnetic field expands</p> Signup and view all the answers

    What is the purpose of the left hand grasp rule?

    <p>To determine the direction of the magnetic field around a wire</p> Signup and view all the answers

    What is self-inductance?

    <p>The property of a conductor that opposes changes in current</p> Signup and view all the answers

    What is the result of varying the strength of the current in the primary conductor?

    <p>An expanding magnetic field is produced</p> Signup and view all the answers

    What is the duration of the induced voltage?

    <p>A fraction of a second</p> Signup and view all the answers

    What is the condition for electromagnetic induction?

    <p>The magnetic field must be changing</p> Signup and view all the answers

    What is the percentage of the maximum current that an inductor reaches after one time constant?

    <p>63.2%</p> Signup and view all the answers

    What is the value of the current after the first time constant if the maximum current is 10 A?

    <p>6.32 A</p> Signup and view all the answers

    After how many time constants does the current in an inductor reach its maximum value?

    <p>5</p> Signup and view all the answers

    What is the increase in current during the second time constant if the maximum current is 10 A?

    <p>2.33 A</p> Signup and view all the answers

    What is the total current in an LR circuit after the completion of the second time constant?

    <p>8.65 A</p> Signup and view all the answers

    What is the reason why most inductors are used in an alternating current (AC) supply?

    <p>To utilize the inductor's properties effectively</p> Signup and view all the answers

    What is the unit of the time constant in an LR circuit?

    <p>Henrys per Ohms</p> Signup and view all the answers

    What is the formula for the time constant in an LR circuit?

    <p>L/R</p> Signup and view all the answers

    What is the direction of the counter-electromotive force (CEMF) in relation to the applied voltage of the conductor?

    <p>In the opposite direction</p> Signup and view all the answers

    When a length of conductor is looped, what happens to the electromagnetic field around each portion of the conductor?

    <p>It cuts across some other portion of the same conductor</p> Signup and view all the answers

    What is the effect of increasing current in Conductor 1 on the magnetic field around Conductor 2?

    <p>The magnetic field expands outward</p> Signup and view all the answers

    What is the result of the expanding field of flux cutting across Conductor 2?

    <p>An induced EMF in Conductor 2</p> Signup and view all the answers

    What is Lenz's law related to?

    <p>The direction of the induced EMF</p> Signup and view all the answers

    What is the term for the EMF produced by a moving magnetic field?

    <p>Counter-electromotive force (CEMF)</p> Signup and view all the answers

    What is the effect of changing the magnetic field strength on a coil of wire?

    <p>It induces a voltage in the coil</p> Signup and view all the answers

    What is the overall effect of the counter-electromotive force (CEMF)?

    <p>To oppose a change in current magnitude</p> Signup and view all the answers

    What happens when a coil is moved into a magnetic field?

    <p>A voltage is generated in the coil</p> Signup and view all the answers

    What is the term for the EMF induced in a conductor carrying a current?

    <p>Self-induced EMF</p> Signup and view all the answers

    What is the purpose of the induced magnetic field according to Lenz's law?

    <p>To keep the magnetic flux constant</p> Signup and view all the answers

    What is the direction of the induced EMF in relation to the battery current and voltage?

    <p>In the opposite direction</p> Signup and view all the answers

    What is the relationship between the speed of coil movement and the induced voltage?

    <p>The induced voltage is directly proportional to the speed</p> Signup and view all the answers

    What is the effect of rotating the coil relative to the magnet?

    <p>It induces a voltage in the coil</p> Signup and view all the answers

    What is the purpose of the left-hand rule for generators?

    <p>To determine the direction of the induced current</p> Signup and view all the answers

    What is the polarity of the induced EMF according to Lenz's law?

    <p>It produces a current whose magnetic field opposes the change</p> Signup and view all the answers

    What happens to the flux field when the switch is opened?

    <p>It collapses</p> Signup and view all the answers

    What is the condition for Faraday's law to apply?

    <p>Any change in the magnetic environment of a coil of wire</p> Signup and view all the answers

    What is the effect of the self-induced voltage on the current when the switch is closed?

    <p>It delays the initial build-up of current</p> Signup and view all the answers

    What is the direction of the induced current in a coil?

    <p>It is in the opposite direction of the magnetic field</p> Signup and view all the answers

    What is the effect of the self-induced voltage on the current when the switch is opened?

    <p>It keeps the current flowing in the same direction</p> Signup and view all the answers

    What is the relationship between the rate of change of primary current and mutual inductance?

    <p>The rate of change of primary current increases with increasing mutual inductance</p> Signup and view all the answers

    What is the purpose of describing series and parallel inductors and the voltage/current relationship?

    <p>To analyze the behavior of inductors in a circuit</p> Signup and view all the answers

    What is the learning objective of describing mutual induction?

    <p>To describe the effect of mutual induction at Level 2</p> Signup and view all the answers

    What happens when the switch is toggled to disconnect the inductor from the power source?

    <p>The inductor tries to oppose the change by inducing a voltage across the inductor.</p> Signup and view all the answers

    What is the effect of the induced voltage across the inductor when it is disconnected from the power source?

    <p>The current flowing through the inductor continues in the same direction.</p> Signup and view all the answers

    What determines the time constant in an LR circuit?

    <p>The amount of inductance and resistance in the circuit.</p> Signup and view all the answers

    What happens to the energy stored in the inductor after five time constants?

    <p>The energy is completely dissipated as heat.</p> Signup and view all the answers

    What is the effect of high circuit resistance on the time constant?

    <p>The time constant decreases.</p> Signup and view all the answers

    What is the purpose of the LR time constant?

    <p>To determine the time required for current to reach a specific value.</p> Signup and view all the answers

    When the inductor is disconnected from the power source, what does it act as?

    <p>A power source.</p> Signup and view all the answers

    What happens to the current flowing through the inductor after the energy is completely dissipated?

    <p>The current falls to zero.</p> Signup and view all the answers

    What type of value is displayed by most multimeters when measuring AC sine waves?

    <p>RMS</p> Signup and view all the answers

    What is the unit of measurement for electrical phase?

    <p>Degrees</p> Signup and view all the answers

    What is the term used to describe the state when the voltage and current sine waves cross the zero line at the same time?

    <p>In phase</p> Signup and view all the answers

    What type of multimeter measures the true value of a sine wave?

    <p>True Value RMS multimeter</p> Signup and view all the answers

    What is the significance of 360° in electrical phase measurement?

    <p>It represents a complete cycle</p> Signup and view all the answers

    What is the relationship between the voltage and current sine waves when they are in phase?

    <p>They cross the zero line at the same time</p> Signup and view all the answers

    What is the result of moving a coil of wire into a magnetic field?

    <p>A voltage is generated in the coil</p> Signup and view all the answers

    What factor increases the mutual inductance between two coils?

    <p>Mounting the coils on a common iron core</p> Signup and view all the answers

    What is the purpose of the induced magnetic field in a coil according to Lenz's law?

    <p>To oppose the change in magnetic flux</p> Signup and view all the answers

    What is the effect of changing the magnetic field strength on a coil of wire?

    <p>A voltage is generated in the coil</p> Signup and view all the answers

    What happens to the induced EMF when the magnetic field strength increases?

    <p>It increases</p> Signup and view all the answers

    What is the direction of the induced current in a coil according to Lenz's law?

    <p>Opposite to the direction of the magnetic field</p> Signup and view all the answers

    What is the effect of a changing magnetic field on a coil?

    <p>It induces a voltage</p> Signup and view all the answers

    What is the purpose of a ferromagnetic core in a transformer?

    <p>To increase the magnetic field strength</p> Signup and view all the answers

    What is the relationship between the speed of coil movement and the induced voltage?

    <p>The induced voltage is directly proportional to the speed</p> Signup and view all the answers

    What is the point at which an additional increase in the magnetising force produces very little increase in magnetic flux?

    <p>Point of magnetic saturation</p> Signup and view all the answers

    What is the effect of rotating a coil relative to a magnet?

    <p>A voltage is generated in the coil</p> Signup and view all the answers

    What happens to the induced voltage when the rate of change of flux increases?

    <p>It increases</p> Signup and view all the answers

    What is the term used to describe the level of residual magnetism in a material?

    <p>Retentivity</p> Signup and view all the answers

    What is the result of moving a magnet towards a coil of wire?

    <p>A voltage is generated in the coil</p> Signup and view all the answers

    What is the result of increasing the number of conductor turns?

    <p>The induced EMF increases</p> Signup and view all the answers

    What is the effect of changing the area of the coil in the magnetic field?

    <p>A voltage is generated in the coil</p> Signup and view all the answers

    What is the force required to remove the residual magnetism from a material?

    <p>Coercive force</p> Signup and view all the answers

    What is the effect of separating the coils by a considerable distance?

    <p>The mutual inductance decreases</p> Signup and view all the answers

    What happens to the magnetic field strength when the current is reduced to zero?

    <p>Some magnetic flux remains</p> Signup and view all the answers

    What happens when the primary current changes in a transformer?

    <p>The induced voltage in the secondary increases</p> Signup and view all the answers

    What is the point at which the reversed magnetising force has flipped enough of the domains so that the net flux within the material is zero?

    <p>Point of coercivity</p> Signup and view all the answers

    What happens to the material as the magnetising force is increased in the negative direction?

    <p>It becomes magnetically saturated in the opposite direction</p> Signup and view all the answers

    What is the result of increasing the current back in the positive direction after the material has been magnetically saturated in the negative direction?

    <p>The magnetic field strength decreases to zero</p> Signup and view all the answers

    What is the hysteresis loop generated by measuring?

    <p>The magnetic flux of a ferromagnetic material while the magnetising force is changed</p> Signup and view all the answers

    What is the primary factor that increases the inductance of a coil?

    <p>The number of layers in the coil</p> Signup and view all the answers

    What is the principle behind mutual inductance?

    <p>Magnetic flux inducing voltage in another conductor</p> Signup and view all the answers

    What is the effect of increasing the number of layers in a coil?

    <p>Increased inductance</p> Signup and view all the answers

    What is the result of a change in flux in one coil in a mutual inductance system?

    <p>An EMF is induced in the other coil</p> Signup and view all the answers

    What is the purpose of layering in coil construction?

    <p>To increase inductance</p> Signup and view all the answers

    What is a characteristic of mutual inductance?

    <p>Circuits are magnetically coupled</p> Signup and view all the answers

    What is the result of positioning two coils so that the flux from one coil links with the turns of the other coil?

    <p>The coils are magnetically coupled</p> Signup and view all the answers

    What is a factor that affects mutual inductance?

    <p>Number of turns in each coil</p> Signup and view all the answers

    What is the effect of increasing the number of poles on a generator?

    <p>An increase in the number of cycles completed in a revolution</p> Signup and view all the answers

    What is the peak-to-peak value of a sine wave?

    <p>The difference between the peak positive and peak negative values</p> Signup and view all the answers

    What is the formula for finding the instantaneous value of a sine wave?

    <p>VINST = VP × sin Ø</p> Signup and view all the answers

    What happens to the period of a sine wave as the frequency increases?

    <p>The period decreases</p> Signup and view all the answers

    What is the result of increasing the speed of a coil spinning in a magnetic field?

    <p>An increase in the frequency of the sine wave</p> Signup and view all the answers

    What is the relationship between the angle of rotation and the instantaneous value of a sine wave?

    <p>The instantaneous value is proportional to the sine of the angle of rotation</p> Signup and view all the answers

    What is the period of a sine wave expressed in terms of?

    <p>Time</p> Signup and view all the answers

    What is the definition of the period of a sine wave?

    <p>The time taken for one cycle</p> Signup and view all the answers

    What is the effect of increasing the permeability of the core material on the inductance of a coil?

    <p>It increases the inductance</p> Signup and view all the answers

    Why is Coil B more inductive than Coil A?

    <p>Because Coil B has a soft-iron core</p> Signup and view all the answers

    What is the result of winding a coil in layers?

    <p>It increases the inductance</p> Signup and view all the answers

    What determines the strength of the magnetic field in a coil?

    <p>The type of core material</p> Signup and view all the answers

    How does the inductance of a coil change when the coil length is varied?

    <p>It increases with decreasing coil length</p> Signup and view all the answers

    What is the effect of using a soft-iron core in a coil?

    <p>It increases the inductance</p> Signup and view all the answers

    What is the relationship between the number of coil layers and the inductance?

    <p>Increasing the number of layers increases the inductance</p> Signup and view all the answers

    What determines the inductance of a coil with an air core?

    <p>The number of turns</p> Signup and view all the answers

    Why does increasing the number of turns in the primary coil not directly increase the induced voltage in the secondary coil?

    <p>Because it increases the counter-electromotive force, reducing the current through the coil</p> Signup and view all the answers

    What happens to the primary magnetic field when current flows in the secondary circuit?

    <p>It weakens</p> Signup and view all the answers

    Why does the applied voltage need to be increased to overcome the counter-electromotive force?

    <p>To increase the current flow in the primary wire</p> Signup and view all the answers

    What is the effect of increasing the current flow in the primary wire on the induced voltage in the secondary coil?

    <p>It increases the induced voltage</p> Signup and view all the answers

    Why does the secondary conductor need to be connected to a circuit for current to flow?

    <p>Because the secondary conductor needs a return path for current to flow</p> Signup and view all the answers

    What is the relationship between the primary and secondary coils in a transformer?

    <p>They are magnetically coupled</p> Signup and view all the answers

    What happens to the voltage in the primary wire when the current flow is increased?

    <p>It increases</p> Signup and view all the answers

    What is the effect of the magnetic field generated by the secondary coil on the primary magnetic field?

    <p>It weakens it</p> Signup and view all the answers

    What is the shape of the most common AC waveform?

    <p>Sine (or sinusoidal)</p> Signup and view all the answers

    What determines the direction of current movement in an AC waveform?

    <p>Generated terminal voltage polarities</p> Signup and view all the answers

    What is the distance from zero to the maximum value of an AC waveform called?

    <p>Amplitude</p> Signup and view all the answers

    What happens to the induced EMF when a conductor is cutting lines of flux quickly?

    <p>It increases</p> Signup and view all the answers

    What does a sinusoidal sine wave represent?

    <p>The value of induced EMF at each instant of time during 360° rotation of the loop</p> Signup and view all the answers

    What is the result of the negative alternation in an AC waveform?

    <p>Current movement in the opposite direction</p> Signup and view all the answers

    What occurs when the primary current changes in a transformer?

    <p>The flux and current in the primary circuit increase until the CEMF and EMF are in balance</p> Signup and view all the answers

    What is the coefficient of coupling when all of the flux of one coil cuts all of the turns of the other coil?

    <p>1</p> Signup and view all the answers

    What is the purpose of the simple AC generator?

    <p>To generate AC</p> Signup and view all the answers

    What happens to the force driving electrons when a conductor is cutting lines of flux quickly?

    <p>It increases</p> Signup and view all the answers

    What happens when a material is magnetically saturated?

    <p>No additional amount of external magnetisation force will cause an increase in its internal level of magnetisation</p> Signup and view all the answers

    What is the formula for mutual inductance between two coils?

    <p>M = K √(L1 × L2)</p> Signup and view all the answers

    What is the effect of magnetic saturation on the mutual induction in the secondary circuit?

    <p>It reduces the amount of mutual induction</p> Signup and view all the answers

    What is the symbol for the coefficient of coupling?

    <p>K</p> Signup and view all the answers

    What is the result of increasing the flux cutting one coil?

    <p>The mutual inductance increases</p> Signup and view all the answers

    What is the relationship between the coefficient of coupling and the mutual inductance?

    <p>M = K √(L1 × L2)</p> Signup and view all the answers

    When a voltage sine wave is applied to a resistance in a circuit, what is the resulting current?

    <p>A sine wave</p> Signup and view all the answers

    What is the condition for two sine waves to be in phase?

    <p>They must go through their maximum and minimum points at the same time and in the same direction</p> Signup and view all the answers

    What happens to the current when the voltage reverses direction in a circuit?

    <p>It also reverses direction</p> Signup and view all the answers

    What is the term used to describe sine waves that are 180 degrees out of phase?

    <p>Out of phase</p> Signup and view all the answers

    What is the relationship between the voltage and current sine waves in a circuit?

    <p>They are always in phase</p> Signup and view all the answers

    What happens to the voltage and current sine waves when they are in phase?

    <p>They add to each other</p> Signup and view all the answers

    What is the condition for multiple sine waves to be in phase with each other?

    <p>They must go through their maximum and minimum points at the same time and in the same direction</p> Signup and view all the answers

    What happens to the current when the voltage increases in a circuit?

    <p>It increases</p> Signup and view all the answers

    Study Notes

    Faraday's Law Practical Example

    • A permanent magnet's movement and a coil of wire can demonstrate Faraday's law.
    • The law states that any change in the magnetic environment of a coil of wire will cause a voltage (EMF) to be induced in the coil.

    Variations of Faraday's Law

    • The change in magnetic environment can be produced by:
      • Changing the magnetic field strength
      • Moving a magnet towards or away from the coil
      • Moving the coil into or out of the magnetic field
      • Rotating the coil relative to the magnet
    • The voltage generated is proportional to the speed with which the coil is moved into the magnetic field.

    Lenz's Law

    • Induced Electromotive Force (EMF) polarity is such that it produces a current whose magnetic field opposes the change that produces it.
    • The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.
    • Left-hand grasp rule can be used to determine the direction of the magnetic field around a wire.

    Electromagnetic Induction

    • Switching the current to a coil on or off creates a magnetic field that builds up or collapses, inducing a voltage in another coil.
    • The movement of the magnetic field is produced by varying the strength of the current in the coil producing the field.
    • The induced voltage is in a direction opposite the magnetic field produced by the current in the primary conductor.

    Self-Inductance

    • A perfectly straight length of conductor has some inductance.
    • Current in a conductor produces a magnetic field surrounding the conductor, which changes when the current changes.

    Mutual Induction

    • The amount of mutual inductance depends on the relative positions of the two coils.
    • Mutual inductance can be increased by:
      • Mounting the coils on a common iron core
      • Increasing the magnetic field strength
      • Increasing the number of conductor turns
      • Increasing the rate of change of flux (frequency)
      • Increasing the permeability of the core

    Primary Current Affecting Induced Voltage

    • The theory of mutual induction leads to transformer operating principles.
    • A changing magnetic field from one coil can induce a voltage in the second coil.

    Time Constant (TC)

    • The time constant is the time required for the current in an inductor to increase to 63.2% of the maximum current.
    • Each TC is equal to the time required for the current to increase by 63.2% of the difference in value between the current flowing in the inductor and the maximum current.
    • Maximum current flows in the inductor after five L/R time constants are completed.

    LR Time Constant Graph

    • The graph illustrates how the current increases by 63.2% of the difference in value between the current flowing in the inductor and the maximum current during each time constant.

    Square Wave, Sawtooth Wave, and Triangular Wave

    • Square waves are commonly used in computer processors.
    • Sawtooth waves can be generated using a DC circuit that measures the voltage at a capacitor that is gradually charged and rapidly discharged.
    • Triangular waves can be generated by processing a square wave through an integrator.
    • The difference between a triangular and a sawtooth wave is the timing associated with the rise and fall of the wave shape.

    Faraday's Law and Electromagnetic Induction

    • A change in the magnetic environment of a coil of wire induces a voltage (EMF) in the coil.
    • The change can be produced by changing the magnetic field strength, moving a magnet towards or away from the coil, or rotating the coil relative to the magnet.

    Variations of Faraday's Law

    • The voltage generated when a coil is moved into a magnetic field is called motional EMF and is proportional to the speed of the coil's movement into the magnetic field.
    • The speed can be expressed in terms of the rate of change of the area that is in the magnetic field.

    Lenz's Law

    • The polarity of the induced EMF is such that it produces a current whose magnetic field opposes the change that produces it.
    • The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.
    • When the flux field is increasing, the induced field acts in opposition to it.

    Electromotive Force (EMF)

    • EMF is induced in a conductor when there is relative motion between the magnetic field and the conductor.
    • The induced EMF is also referred to as counter-electromotive force (CEMF) or back EMF.
    • The polarity of the counter-electromotive force is in the opposite direction of the applied voltage of the conductor.

    Inductance and Inductor

    • Inductance is the property of a conductor that opposes changes in current.
    • When the switch is closed, the self-induced voltage opposes the initial build-up of current by opposing the battery voltage.
    • When the switch is opened, the self-induced voltage keeps the current flowing in the same direction by aiding the battery voltage.

    Series and Parallel Inductors

    • Series and parallel inductors have a voltage/current relationship.

    Mutual Induction

    • Mutual induction is the process by which a changing magnetic field induces a voltage in a nearby conductor.
    • The rate of change of primary current and mutual inductance affects the induced voltage.

    Inductor Resistor (LR) Circuit

    • When the switch is toggled to disconnect the inductor from the power source, the inductor tries to oppose the change by inducing a voltage across the inductor.
    • The polarity of the induced voltage is the same as the original power source, keeping the current flowing through the inductor in the same direction.
    • The energy stored in the inductor is dissipated by the resistor as heat after five time constants.

    LR Time Constant

    • The LR time constant (TC) is a valuable tool for determining the time required for current in an inductor to reach a specific value.
    • The time constant depends on the amount of inductance (L) and the amount of resistance (R) in the circuit.

    AC Sine Wave

    • Most multimeters measure in average but display in RMS (Root Mean Square) values.
    • RMS is the accepted and most-used value of a sine wave.

    Phase

    • Phase is a frequently used term with AC, applied to the periodic changes of quantities such as voltage or current in an AC circuit.
    • Electrical phase is measured in degrees, with 360° corresponding to a complete cycle.
    • When the voltage and current sine waves cross the zero line at the same time, they are said to be 'in phase'.

    Faraday's Law

    • Any change in the magnetic environment of a coil of wire will cause a voltage (EMF) to be induced in the coil.
    • The change can be produced by changing the magnetic field strength, moving a magnet towards or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, and so on.
    • The voltage generated when a coil is moved into a magnetic field is called motional EMF and is proportional to the speed with which the coil is moved into the magnetic field.

    Lenz's Law

    • The polarity of the induced EMF is such that it produces a current whose magnetic field opposes the change that produces it.
    • The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.
    • If the magnetic flux is increasing, the induced field acts in opposition to it.

    Mutual Inductance

    • When a conductor's magnetic flux induces voltage in another electrically isolated conductor, it is called mutual inductance.
    • Mutual inductance depends on the number of turns in each coil, physical size of each coil, permeability of each coil, and position of coils with respect to each other.
    • Mutual inductance allows the energy from one coil to be transferred or coupled to the other coil.
    • The amount of mutual inductance depends on the relative positions of the two coils.

    Primary Current Affecting Induced Voltage

    • If we supply power to a large (primary) wire wrapped around a ferromagnetic core and have a corresponding smaller (secondary) wire unpowered wrapped around the same core, the change in current in the primary will induce a voltage in the secondary.
    • Increasing the magnetic field strength, number of conductor turns, rate of change of flux (increasing frequency), and permeability of core(s) will increase the induced EMF.

    Hysteresis Loop

    • The hysteresis loop is generated by measuring the magnetic flux of a ferromagnetic material while the magnetising force is changed.
    • The greater the amount of current applied, the stronger the magnetic field in the component.
    • When almost all of the magnetic domains are aligned, an additional increase in the magnetising force will produce very little increase in magnetic flux.
    • The material has reached the point of magnetic saturation.

    Coil with a Metal Core

    • When the current is reduced to zero, some magnetic flux remains in the material even though the magnetising force is zero.
    • This is referred to as the point of retentivity and indicates the remanence or level of residual magnetism in the material.
    • As the magnetising force is reversed, the flux is reduced to zero.
    • This is called the point of coercivity (the reversed magnetising force has flipped enough of the domains so that the net flux within the material is zero).

    Sine Wave

    • The period of a sine wave is expressed in time, usually as a fraction (or decimal) of a second.
    • The period of a sine wave is the time taken for one cycle.
    • An increase in the number of poles causes a corresponding increase in the number of cycles completed in a revolution.
    • Peak-to-peak voltage or current is the magnitude of the voltage or current between the peak positive and peak negative values.
    • Instantaneous voltage or current is the value at any time on the sine wave.
    • The instantaneous value of the sine wave can be found using the formula: VINST = VPK × sin Ø, where Ø is the angle of rotation of the cycle.

    Factors Affecting Inductance

    • Varying the coil length varies the inductance
    • The type of core material used with the coil affects inductance, with a soft-iron core being a better path for magnetic lines of force than an air core
    • The permeability of the core material increases the inductance of the coil
    • The strength of the magnetic field also depends on the permeability of the core material

    Number of Coil Layers

    • Winding the coil in layers increases the inductance
    • Coil layering affects the flux movement and the number of flux loops during flux movements
    • The rate of decreasing magnetic flux affects the induced voltage

    Coefficient of Coupling

    • The coefficient of coupling between two coils is the ratio of the flux cutting one coil to the flux originated in the other coil
    • The coefficient of coupling is designated by the letter K and approaches unity in certain types of coupling devices
    • Mutual inductance (M) is expressed in terms of the inductance of each coil and the coefficient of coupling K: M = K √L1 × L2

    Magnetic Saturation

    • When a material is magnetically saturated, no additional amount of external magnetization force will cause an increase in its internal level of magnetization
    • After saturation, no increase in the amount of current through the primary circuit will increase the amount of mutual induction that is induced EMF in the secondary circuit

    AC Waveforms

    • A sinusoidal sine wave represents induced EMF for a single coil rotated through a uniform magnetic field at a constant speed
    • The most common AC waveform is a sine (or sinusoidal) waveform
    • AC flows first in one direction and then in the opposite direction, with current amperage being a function of time
    • DC amperage is constant

    Sine Waves

    • A conductor cutting lines of flux quickly produces a greater force to drive electrons and hence a greater potential difference
    • Each cycle of the sine wave consists of two identically shaped variations in voltage
    • The amplitude of the positive alternation and the amplitude of the negative alternation are the same
    • Sine waves can be in phase or out of phase with each other

    Simple AC Generator

    • A simple AC generator produces a sinusoidal sine wave showing the value of induced EMF at each instant of time during 360° rotation of the loop

    Sine Waves in Phase and Out of Phase

    • When a voltage sine wave is applied to a resistance in a circuit, the resulting current is also a sine wave following Ohm's law
    • Sine waves in phase with each other have maximum and minimum points at the same time and in the same direction
    • Sine waves out of phase with each other do not have maximum and minimum points at the same time and in the same direction

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