Ch. 7 Electromagnetism

Chapter 7: Electromagnetism 09/30/25

Magnetism

Definition of Magnetism

  • Definition: Magnetism is the ability of a lodestone or magnetic material to attract specific metals, namely iron, nickel, and cobalt.

Magnetic Poles

  • Magnetic Pole: Regions of magnetism always exist as a dipole. This means that magnets have two poles: a north pole and a south pole. Even at the smallest scale, magnetic monopoles do not exist.

Types of Materials

  • Materials can be categorized based on their magnetic properties:

    • Ferromagnetic: Strongly attracted to magnets or magnetic fields.

    • Paramagnetic: Slightly attracted to magnets.

    • Diamagnetic: Weakly repelled by magnets.

    • Nonmagnetic: Do not respond to magnetic fields.

Four Types of Magnetic Materials

  1. Ferromagnetic Materials:

    • These materials exhibit a strong attraction to magnets. Examples include iron, nickel, and cobalt.

  2. Paramagnetic Materials:

    • These materials exhibit a weak attraction to magnetic fields.

  3. Diamagnetic Materials:

    • These materials are repelled by magnets, albeit weakly.

  4. Nonmagnetic Materials:

    • These materials show no magnetic attraction or repulsion characteristics.

Magnetic Induction

  • Concept: When a non-magnetized iron bar is brought into an external magnetic field, the dipoles within the bar align themselves along the magnetic field lines.

Magnetic Domains

  • Magnetic Domain: A group of atoms aligned in the same direction that exhibit a net magnetic field.

Magnetic Field

  • A magnetic field surrounds either a magnet or a moving electric current.

    • Units of Measurement:

    • Gauss (G)

    • Tesla (T)

    • Conversion: 1 tesla = 10,000 gauss.

    • Electron Spin: A metaphor used to explain magnetism, likening it to a boat with two people rowing (a reference to the spinning motion of electrons).

The Laws of Magnetism

  1. Repulsion-Attraction:

    • Like poles repel each other, whereas opposite poles attract.

  2. Magnetic Poles:

    • Magnetic field lines, also referred to as magnetic flux lines, are synonymous with one another. These flux lines never intersect or touch.

  3. Inverse Square Law:

    • Specifies that the strength of a magnetic field decreases with the square of the distance from the source.

Mutual Induction

  • Definition: The phenomenon of inducing electromagnetic force (EMF) in one coil due to the varying current supplied to another coil nearby.

    • Components:

    • Two Coils: Two coils are placed in proximity to each other.

    • Varying Current: A varying current is supplied to the primary coil, which induces a current in the secondary coil.

Helices and Solenoids

  • Helix: A coiled conductor.

  • Solenoid: A helix carrying an electric current, which generates a magnetic field around it.

  • Electromagnet: An iron core placed in the center of a solenoid that enhances its magnetic field.

Electromagnetic Induction

Definition

  • Definition: The production of electrical current in a conductor as a result of a changing magnetic field around it.

Michael Faraday's Contribution

  • Michael Faraday discovered that voltage (or EMF) can be induced through three methods:

    1. Move a conductor through a stationary magnetic field.

    2. Move magnetic lines of force across a conductor.

    3. Vary the strength of a stationary magnetic field through a conductor.

Self-Induction

  • Definition: A phenomenon that occurs in a single coil. It arises when alternating current flowing through the coil creates an outward expanding and varying magnetic field that, in turn, produces an electric field (or current).

Factors Affecting Induced EMF

  • Strength of the magnetic field

  • Speed of motion between the field lines and the conductor

  • Angle between the magnetic field lines and the conductor

  • Number of turns in the conducting coil

Generator

Definition

  • Definition: A device designed to convert mechanical energy into electrical energy by producing electrical current.

Functionality

  • Generates alternating current (AC) through the utilization of slip rings (which prevent twisting while spinning) in conjunction with an armature (the component that rotates and carries the conductor).

  • Produces direct current (DC) by replacing slip rings with a commutator ring.

Motor

Definition

  • Definition: An electromagnetic device that transforms electrical energy into mechanical energy.

Components of an Induction Motor

  • Rotor: The rotating component of the motor.

  • Stator: The stationary part of the motor that creates a magnetic field, necessary for the rotor to turn.