310102iB 2 Magnetism, Electromagnetism and Electromagnetic Induction Part B 2017 (TF) (Self and Mutual Induction) 2017 (TF)

Magnetism, Electromagnetism, and Electromagnetic Induction

Objectives

• Understanding Electromagnetism:

  • Describe the fundamental concept of electromagnetism and essential design considerations for related devices.

• Induced Voltage Generation:

  • Explain how voltage is induced in a closed circuit.

• Electromagnetic Induction Process:

  • Understand the process and principles of electromagnetic induction.

Lenz’s Law of Induction

• Definition:

  • An induced EMF in a closed circuit generates a current that opposes the change responsible for its production.

Magnetic Circuits

• Conductor Movement:

  • The direction of conductor movement is determined by the arrangement of magnetic fields and the right-hand rule of electromagnetism (first finger - direction of field, second finger - direction of current).

Electromagnet Construction

• Creation of an Electromagnet:

  • Wrapping a wire around an iron or steel core and passing current through it magnetizes the core.

• Magnet Core Properties:

  • If the core is soft iron, magnetism fades when the current stops.

• Factors Affecting Electromagnetic Strength:

  1. Amount of current flowing through the coil.

  2. Number of turns of wire in the coil.

  3. Material type of the core used.

Magnetic Domains

• Configuration Changes:

  • Magnetic domains within the core become polarized in accordance with the alternating current, as shown in magnetic flux changes (Figure 8).

Eddy Currents

• What are Eddy Currents:

  • Eddy currents are looped electrical currents that form in conductive materials when exposed to changing magnetic fields (Figure 9).

Reducing Iron Losses

• Laminations and Material Choices:

  • Utilizing laminations and silicon steel alloys minimizes iron losses in electromagnetic applications. (Figure 10)

Inducing EMF

• Requirements for Induction:

  • To induce an electromotive force (emf), three conditions must be met:

    1. A magnetic field must be present.

    2. A conductor must be available.

    3. There must be relative motion between the conductor and the magnetic field.

Factors in Induced EMF

• Dependence on Motion and Field:

  • The rate at which a magnetic field is intersected by a conductor directly affects the induced emf magnitude:

    • Cutting through 100 million lines of force per second induces one volt in the conductor.

Influences on Induced Voltage

• Three Key Factors:

  1. Flux density (concentration of magnetic field lines).

  2. Length of the conductor interacting with the magnetic field.

  3. Rate of cutting across lines of force.

Faraday’s Law of Induction

• The Law Defined:

  • States that changing the number of magnetic field lines passing through a coil induces a voltage proportional to the rate of that change.

Electromagnetic Induction Overview

• Key Principle:

  • Relative motion between a conductor and a magnetic field results in voltage induction.

Self-Induction

• Mechanism Explained:

  • Like Faraday’s law, self-induction involves voltage induction due to relative motion between the conductor and magnetic field, underlined by Lenz's law:

    • The induced current will always oppose the change in current that created it.

Effects of Induced Voltage

• Counter EMF:

  • The induced voltage or counter electromotive force (EMF) can be influenced by:

    • The rate of change in the magnetic field or current.

    • The number of coil turns resulting in interaction.

Inductance

• Definition of Inductance:

  • A circuit with a coil resists changes in current, quantified as inductance.

• Unit of Inductance:

  • The Henry (L), marked by the relationship where one volt is induced when current changes at a rate of one ampere per second.

Mutual Induction

• Concept of Mutual Induction:

  • Occurs in two coils sharing a common core:

    • When current passes through the primary coil, an expanding magnetic field induces voltage in the secondary coil. Conversely, stopping the current leads to a collapsing field which again induces voltage.

  • The secondary voltage can be adjusted by modifying the number of turns in the wire within the magnetic field (notable in ignition coils).

Transformers and AC Signals

• Utilizing AC Supply:

  • The transformer operates to change secondary voltage by altering the number of turns in AC systems.