What is electromagnetic induction?

The production of an emf in a circuit when the magnetic flux through it changes.

How is magnetic flux calculated for a uniform field through a flat surface?

$\Phi_m=BA\cos\theta$, where $\theta$ is the angle between the magnetic field and the area vector.

What determines the induction effect in a magnet-and-coil experiment?

Relative motion between the magnet and coil; either object can move.

How can magnetic flux through a circuit change?

A change in magnetic-field strength, surface area, or surface orientation can change the flux.

What is Faraday’s law for a coil with $N$ identical turns?

$\varepsilon=-N\frac{d\Phi_m}{dt}$, when each turn experiences the same magnetic flux.

ElectromagnetismLesson 1 of 2 in the course Electromagnetic Induction

Faraday’s Law: Magnetic Flux and Electromagnetic Induction

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson explores Michael Faraday’s early experiments and the observations that led to the discovery of electromagnetic induction. These experiments show that a changing magnetic field can produce an emf and, in a closed circuit, an induced current.

In 1831, Michael Faraday investigated how magnetic fields that change with time affect circuits. When a bar magnet is pushed into a coil, an emf is induced in the coil. Pulling the magnet out induces an emf of the opposite sign. Reversing the magnet’s poles also reverses the direction of the induced emf.

All flashcards

What is electromagnetic induction?: The production of an emf in a circuit when the magnetic flux through it changes.
How is magnetic flux calculated for a uniform field through a flat surface?: $\Phi_m=BA\cos\theta$ , where $\theta$ is the angle between the magnetic field and the area vector.
What determines the induction effect in a magnet-and-coil experiment?: Relative motion between the magnet and coil; either object can move.
How can magnetic flux through a circuit change?: A change in magnetic-field strength, surface area, or surface orientation can change the flux.
What is Faraday’s law for a coil with $N$ identical turns?: $\varepsilon=-N\frac{d\Phi_m}{dt}$ , when each turn experiences the same magnetic flux.

Quiz questions

For a uniform magnetic field through a flat surface, what is the magnetic flux if $\theta$ is measured from the area vector?Answer: $\Phi_m=BA\cos\theta$
What is the SI unit of magnetic flux?Answer: The weber (Wb)
A coil has $N$ turns, and every turn experiences the same flux $\Phi_m$ . Which expression gives the induced emf?Answer: $\varepsilon=-N\frac{d\Phi_m}{dt}$
A 200-turn square coil has side length $0.25\,\text{m}$ . A perpendicular magnetic field changes at $0.040\,\text{T/s}$ while the coil’s area and orientation remain fixed. What is the emf magnitude?Answer: $0.50\,\text{V}$
In a two-circuit induction experiment, what causes a brief current in the nearby circuit when the first circuit’s switch is closed?Answer: The rising current in the first circuit creates a changing magnetic field.

Based on University Physics Volume 2 by Samuel J. Ling, William Moebs, Jeff Sanny (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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