Physical Science - Chapter 18.3 Notes

🎀 The Discovery of Induction

While it was known that electricity creates magnetism, two scientists—Joseph Henry (US) and Michael Faraday (UK)—independently discovered the reverse: magnetism can produce electricity.

• Faraday’s Breakthrough: Faraday receives primary credit due to his detailed documentation and publication.

• The Critical Observation: In his "iron ring" experiment, Faraday realized that a static magnetic field produces no current. He observed the galvanometer needle move only when the magnetic field was changing (the moment the switch was opened or closed).

🌸 Electromagnetic Induction

Definition: The process of generating an electric current by moving a conductor through a magnetic field or by changing the magnetic field surrounding a conductor.

• Directional Flow: The induced current reverses direction whenever the direction of the magnetic field's motion changes.

• Increasing Current Magnitude: 1. Velocity: Increasing the speed of the relative motion between the magnet and the wire. 2. Coil Density: Increasing the number of loops (turns) in the wire coil.

🎀 Generators

A generator is a device that converts mechanical energy into electrical energy through electromagnetic induction.

• The Mechanism: A mechanical source (like a hand crank or a steam turbine) provides circular motion to rotate a wire coil within a stationary magnetic field.

• Transfer of Power: Slip rings are attached to the rotating coil, allowing the induced current to flow from the moving parts to a stationary external circuit.

🌸 Transformers

Transformers are used to change the voltage of alternating current (AC) to ensure it is safe and efficient for different uses.

• Primary Coil: Receives the incoming AC, turning the iron core into a temporary electromagnet.

• Magnetic Flux: Because AC constantly changes direction, it creates a constantly changing magnetic field.

• Secondary Coil: This changing field induces a new current in the secondary wire loops.

Types of Transformers:

1. Step-Up Transformer: Increases voltage for long-distance transmission. It has more windings on the secondary coil than the primary.

2. Step-Down Transformer: Decreases voltage for household use (e.g., dropping 22,000V down to 120V). It has fewer windings on the secondary coil.

🩰 Academic Reflection

Study Tip: Remember that induction requires change. If the magnet is not moving relative to the wire, the current is zero. 🌸✨