Hewitt-Drew-it! 102. Electromagnetic Induction

History, explanations, and implications of E&M inductions.

 

Collapsing Solenoid

A slinky is stretched out on a glass rod and connected to 120 VAC. When power is applied, the slinky immediately collapses due to Lenz's Law.

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Lenz's Law

Two bar magnets of the same size are dropped through an aluminum tube and a glass tube. The magnet dropped in the glass tube falls at the normal rate of acceleration due to gravity, but the magnet falling through the metal tube is slowed. This slowed acceleration occurs because the falling magnet induces currents inside the metal tube. The induced currents then produce a small magnetic field that opposes the direction of the original magnetic field. This effect is known as Lenz's Law, a result of Faraday's law of induction.

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MIT 8.02 Electricity and Magnetism Lecture 17

MIT 8.02 Electricity and Magnetism, Spring 2002

Professor Walter Lewin

Motional EMF, Dynamos, Eddy Currents, Magnetic Braking.

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MIT 8.02 Electricity and Magnetism Lecture 16

MIT 8.02 Electricity and Magnetism, Spring 2002

Professor Walter Lewin

Electromagnetic Induction, Faraday's Law, Lenz Law, Complete Breakdown of Intuition, Non-Conservative Fields.

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Lenz's Law with Copper Pipe

A magnet is dropped down a conducting copper pipe and feels a resistive force. The falling magnet induces a current in the copper pipe and, by Lenz's Law, the current creates a magnetic field that opposes the changing field of the falling magnet. Thus, the magnet is "repelled" and falls more slowly.

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Ring Falling in a Magnetic Field (MIT Tech TV)

Three aluminium objects are dropped through a magnetic field. The objects move slower entering and leaving the field due to changes in the flux through the object. The change in the flux through a conductor results in a force which opposes additional flux change. As a result the force opposes the motion and slows the object's fall. This demonstration illustrates Faraday's and Lenz's law.

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Electromagnetic induction

These animations show a magnet approaching a conducting coil, then getting farther. The magnetic field lines caused by the magnet change color when they get through the coil. The inducted current in the coil is represented by red spheres in motion (they move in the direction of conventional current).

Other animations by Yves Pelletier