Jumping Wire

What it shows:

A current carrying wire in a magnetic field experiences a force at right angles to both the field and current directions. The wire will jump up or down, depending upon the current direction.

How it works:

On a microscopic scale, the electrons in the wire experience a Lorentz force due to the magnetic field,



the force perpendicular to both field and velocity vector. On the macroscopic scale, it's the interaction of current and field.

To do this on a grand scale, a current of 60A supplied by a battery charger 1 passes through a braided ground wire and between the poles of a large (0.3T) Magnetron magnet. 2 A pulse of current jerks the wire up from the magnet. Reverse the charger clips, and the wire jerks down.

figure 1. Wire and Magnetron magnet.

jump wire

Setting it up:

Lecture bench mounted with the wire held at both ends using lab stands and clamps. If it needs to be mounted on a (metal) cart, make sure the lab stands are insulated! Enough slack should be given so that the wire is free to clearly jump up or down. Only a brief pulse of current should be applied because things get very hot.

Comments:

This demo can be done on a smaller scale using standard clip leads, a smaller Magnetron and a 6V rechargeable cell. 3

1 Powermate Fleet 141-060A Battery Charger.
2 Crucible 3250 gauss Magnetron magnet
3 Dynasty 6V 7 amp. hr. cell, Johnson Controls, Milwaukee Wi.