Build an Electric motor

In this activity, we are going to build a homopolar motor. “Homo” means same. It means that the electrical polarity of the conductor and the magnetic field do not change.

The motor is driven by Lorentz force. A conductor with a current flowing through it when placed in a magnetic field which is perpendicular to the current feels a force called Lorentz force in the direction perpendicular to both magnetic field and current.

Things needed:

• 1 AA battery
• 1 Drywall screw (made of Iron)
• Some neodymium disc magnets (1-2 cm diameter)
• A wire

Experiment:

1. Attach 3 or 4 neodymium disc magnets to the screw head.
2. Suspend the assembly to the negative end of the AA battery through the tip of the screw.
3. Now holding the battery in your left hand with the screw and magnet suspended, attach the positive end of the battery to the side of the neodymium magnets with the help of a wire.

Observation:

When the positive end of the battery is connected to the side of neodymium magnets with a wire, the screw and the magnet will start rotating at high speed. Care should be taken at high speeds as the magnet may get thrown at a velocity. Also, the battery, nail and the magnet may heat up quickly if used continuously.

Explanation:

Here the magnetic field is parallel to the axis of rotation and the current direction as it enters the side of the neodymium magnet to the center of the neodymium magnet is perpendicular to the magnetic field. Due to this Lorentz force act on the (perpendicular to both magnetic field and current) side of the neodymium magnet and since it is hinged at the center, it rotates.

Try this:

Instead of touching the side of the neodymium magnets with the wire, if you the touch the bottom center to the neodymium magnet, it will not rotate since the current is no longer perpendicular to the magnetic field.