Physics Demo Number: 144

Approximate Run Time: 3 min

Eddy Currents with Long Al Tube and Cylindrical Magnet

Demo Description

A long Al tube can have two different close-fitting cylinders dropped down its inner surface from the top.

One cylinder contains a magnet. The other cylinder is identical in outward appearances, but has no magnet inside.

The difference in transit times for the two cases is quite impressive.

Scientific Principles

• Eddy current damping

Equipment

• Al tube

• Two blue cylinders

Equipment Location

• Al tube hangs horizontally on shelves near [B-3-3] level.

• Rest of components in Kit 144 on [B-2-3]

1

2

Instructions

The first photo shows the Al tube hanging from one of the standard setup poles. The second photo gives a closer view of the top of the tube and the two cylinders.

When one places the non-magnetic cylinder in the top of the tube and lets it go, it exits at the bottom of the tube in one second or less.

The magnetic blue cylinder takes 10 or more seconds to make the same trip through the tube.

Writeup created by David A. Burba

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