Capitulo 9 parte 1

Summary

The lesson begins Chapter 9 with an introduction to Faraday’s law of induction, which concerns magnetic fields that change over time, unlike the constant fields studied previously.

The instructor explains that the phenomenon was discovered experimentally in 1831, independently by Faraday in England and Henry in the United States. A changing magnetic field can induce an electromotive force (EMF) in a conductor. This EMF acts like a voltage source—something like an apparent or “imaginary” battery—and can drive a current even when no battery is connected.

First Experiment

1. Set up a closed conducting-wire loop with an ammeter to measure current.
2. Bring a magnet toward the loop, then move it away.
3. The changing magnetic field causes the ammeter to register a current, even though there is no battery in the circuit.
4. This demonstrates that a changing magnetic field induces an EMF and current.

The instructor then introduces a second experiment, but its details are not included in this excerpt.

Speakers and Sources

• Speaker: An unnamed instructor or narrator explaining the lesson.
• Historical figures mentioned: Faraday and Henry, who are discussed but do not speak in the excerpt.