Physics Demo Number: 044

Approximate Run Time: 8 min

Elihu Thomas Popper or Eye-Grabbing Lenz's Law

Demo Description

The Popper can be made to eject  aluminum and copper annular rings placed over its iron shaft. A light bulb can also be lit up by the induced current.

Scientific Principles

• Lenz's Law - the direction of an induced current must be such that its own magnetic field will oppose the action that produced the induced current.

• Electromagnetic Induction

Equipment

• The apparatus includes a popper that ejects Al and Cu annular rings placed over the vertically adjustable center iron shaft.

• A sealed torroidal-coil and light bulb combination is an accessory item in the Kit.

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Equipment Location

• Kit (044) on [B-3-4].

Instructions

When the power cord is plugged into a wall outlet, the Popper will eject Al and Cu annular rings placed over the vertically adjustable center iron shaft (provided that the rings have no radial slit cut in them).

There is indeed a copper ring with a radial slit to show the effect of no induced current in the ring.

One may hold a ring over the energized shaft and detect a large temperature rise in the ring.

By placing the sealed torroidal-coil light bulb combination (shown in the second picture) atop the energized iron core one notes the bulb lights up, even if the whole bulb assembly sits at the bottom of a beaker of water.

[One should note that the action of this apparatus is really more involved than Lenz's Law , but most people prefer to use it as an eye-catching illustration-of-concept of the Law anyway.]

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Writeup created by David A. Burba

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