The Homopolar Motor

Scientific Principles:

The homopolar motor is based on physics laws such as Lorentz force, electromagnetism, and torque.

• Lorentz force- combination of electric and magnetic force on a point charge due to electromagnetic fields.

• Torque-the measurement of force of an object rotating around a pivot

Research/ Investigation Questions

Which of the materials provided for this project are electrical conductors? Which are electrical insulators?

The copper wire and the magnets are both electric conductors. The battery is unique because the outside of it is an insulator and the inside a conductor.

How can you arrange the circuit components so a battery causes a current to flow along a conducting wire? How do you know a current is flowing?

By placing the magnet under the battery and the wire in a rectangular shape around this, current will flow through the copper wire. You will know current is flowing because the wire will spin around the battery and magnet.

What force is felt by a charged particle in a uniform electric field? What force is felt by a charged particle in a uniform magnetic field? How can you use a right-hand rule to compare these forces?

The force felt by particles in both the electric and magnetic fields is Lorentz force, which is a force that measures electromagnetic force. When it comes to right-hand rule, magnetic force is usually measured as going counter clockwise, with the motion going upward. But because homopolar motors are metamaterials, they have a negative refractive index and can spin clockwise, following left-hand rule.

What tools and materials would you use, and how would you use them, to demonstrate the effect a uniform magnetic field has on a current-carrying wire placed in it?

You could use a battery, copper wire, and rare earth magnet to demonstrate this. These materials are used to construct a homopolar motor.

How can you use the available materials to construct a homopolar motor? When the motor is operating, what path does the current take to complete the circuit?

Place the magnets under the battery and bend the copper wire into a rectangular shape around the battery and magnets. The current spins in a circular motion around the battery, which causes the wire to spin.

What do you observe when you operate the homopolar motor? Is there more than one magnetic force involved? How can you use a right-hand or left-hand rule to understand the direction of the magnetic force(s) involved in the operation of the homopolar motor?

The wire spins on the homopolar motor either clockwise or counterclockwise depending on what pole of the magnets is touching the battery. There are two magnetic forces: the positive one and the negative one. If the battery is spinning counterclockwise, the magnetic force follows right hand rule. If it spins clockwise, it follows left hand rule.

Is there any way to reverse the rotation of the homopolar motor? If so, how can you demonstrate this? If the direction can't be reversed, why not?

Homopolar motors are always reversible thanks to the magnet’s two magnetic fields. This can be demonstrated by flipping the magnets at the bottom of the battery.

Is there a net force on the wire portion of the homopolar motor? If so, what is it? If not, why not?

The net force is found using the formula for Lorentz force, which measures electromagnetic force. The formula is F=q(E + v x B) where a particle of charge q moves with velocity v in the presence of an electric field E and a magnetic field B.

Is there a net torque on the wire portion of the homopolar motor? How do you know?

The net torque is zero because the rectangle wire is rotates around the top point of the rectangle and both ends of it are equal. Also the net force is equal

For a rectangular configuration of wire used as the rotating part of a homopolar motor, what information would you need, including any measurements you would need to make, to calculate the magnitude and direction of the torque experienced by this piece of wire?

Length- how long is each half of the wire from the top view. This will help us find torque.

Magnet side-Is the magnet touching the battery on it’s positive or negative end? This will help us with direction.

Mass of wire- Helps us find force

Acceleration of wire- helps with finding force.

Choose one straight segment of wire in your homopolar motor. What is the magnitude and direction of the force acting on this section of wire when the motor is operating?

0.7 Ncm counterclockwise.

Demonstrate how to construct and operate a rectangular homopolar motor and determine the magnitude of the torque exerted on it.

Place the magnets flat under the battery. Bend a copper wire in a rectangular shape around this.