ELECTROMAGNETIC-INDUCTION-FINAL

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Electromagnetism Led by Jana Bay Induction

Electromagnetic Induction

  • Learner Objectives:

    • Infer that the relative motion of a magnet to a conductor induces current.

    • Construct a device that operates on electromagnetic effects.

Historical Background

  • Hans Christian Oersted (Lesson 3.2): Discovered that electric current can produce a magnetic field.

  • Joseph Henry (1797-1878) and Michael Faraday (1791-1867): Conducted experiments demonstrating that magnetism can produce electric current.

    • Henry discovered before Faraday but Faraday published results earlier.

  • Emphasis on the symmetry in nature leading to further exploration of electromagnetic effects.

Faraday’s Discovery

  • Moving a Magnet through a Coil of Wire:

    • Induced electric current when moving a magnet through a coil.

    • Direction of current changes based on the magnet's movement (pulled out vs pushed in).

    • Faster movement results in a greater electric current due to rapid change in the magnetic field.

Observations with Galvanometer

  • Galvanometer Function:

    • Detects small currents; pointer movement indicates current generation.

    • Stationary magnet yields no movement of galvanometer unless the coil moves.

    • Greater deflection occurs when the magnet is moved faster through the coil.

Induction Techniques

  • Methods to Induce Current:

    1. Reverse the pole of the magnet.

    2. Pull the magnet away from the solenoid.

Mutual Induction

  • Occurs when:

    • Closing the switch in a circuit creates a magnetic field that induces current in a secondary coil.

    • Opening the circuit induces current in the opposite direction in the secondary coil due to demagnetization.

Lenz's Law

  • Developed by Heinrich Lenz (1804-1865).

  • Describes the relationship between the inducing field and the induced current:

    • The induced current's magnetic field opposes the change that created it.

Applying Lenz’s Law

  • Direction of Induced Current:

    1. North pole moving away induces a magnetic field to oppose this change.

    2. North pole approaching induces a magnetic field to repel the magnet.

  • Use of right-hand rule to determine induction directions.

Generators Overview

  • Electric Generators:

    • Converts mechanical energy into electrical energy.

    • Simplest generator acts as both a motor (when powered) and generator (when mechanically turned).

Types of Generators

  1. Commercial Generators:

    • Multiple coils with many windings, often using electromagnets.

  2. DC Generators:

    • Produces a direct current (pulsating in one direction).

Signal Transmission in Power Plants

  • Electricity transmitted over long distances at high voltage.

  • Only changing magnetic fields induce current, steady fields do not.

Transformers

  • Also known as Faraday's Ring.

  • Transforms voltage difference based on changing the number of loops in the primary or secondary coils.

Types of Transformers

  • Step-Up Transformer:

    • Increases voltage; secondary has more loops than primary.

  • Step-Down Transformer:

    • Decreases voltage; primary has more loops than secondary.

Key Terms

  • Alternating Current (AC): Changes direction regularly.

  • Direct Current (DC): Flows in one direction.

  • Electromagnetic Induction: Creating current by changing magnetic field.

  • Generator: Converts mechanical to electrical energy.

  • Induced Current: Current generated by changing magnetic field.

  • Mutual Induction: Changing current in one coil induces current in another nearby coil.

  • Transformer: Uses electromagnetic induction to adjust voltage.