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Title: Exploring Electric Motors (Electromagnetism)
Principle(s) Investigated:
- Electromagnetism
- Lorentz Force
- Homopolar Motor
HS-PS2.B: Types of Interactions
Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. Magnets or electric currents cause magnetic fields; electric charges or changing magnetic fields cause electric fields. (HS-PS2-4),(HS-PS2-5)
HS-PS2-5.
Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.
Materials:
- AA battery
- Neodymium magnet
- Copper wire
- Needle nose pliers
- Screw
You can obtain these items from hardware stores like Lowes and Home Depot. You can also obtain them from a hobby shop such as Hobby Lobby. Alternatively, you can order them online from Amazon.com (which is where I purchased the magnets and wire).
Procedure:
- Introduce
- Break into groups of 3-4
- Instruct students that they will be constructing an electric motor.
- Go over safety precautions.
- Have students gather the materials.
- Give students time to try to figure out how to construct the motor.
- Demonstrate how to build the first motor:
- Attach the magnet to the screw.
- The screw can be magnetically attached to the negative end of the battery.
- If the copper wire is coated strip the wire.
- Bend the wire so that one end touches the positive battery terminal and place one finger on top of it to keep the connection. Touch the other end of the wire to the magnet.
- As the copper wire grazes the magnet the screw will begin to spin.
- Demonstrate how to build the second motor:
- Attach the magnet to the negative side of the battery.
- If the copper wire is coated strip the wire.
- Bend the wire so that one end touches the positive battery terminal and the other touches the magnet under the negative battery terminal. You'll need copper wire to bend around two sides of the battery to stay balanced.
- As the copper wire grazes the magnet the wire will begin to spin.
- Allow students to create their own shapes with the copper wiring for their motor.
Student prior knowledge:
- Students will know about electrical conductive materials (copper wire and neodymium magnet in this case).
- Students will know about magnetic fields (north & south).
- Students will know about current carrying conductors.
Explanation:
Electromagnetic technology began with Faraday’s discovery of induction in 1831. His demonstration that a changing magnetic field induces an electric current in a nearby circuit showed that mechanical energy can be converted to electric energy. It provided the foundation for electric power generation, leading directly to the invention of the dynamo and the electric motor. Faraday’s finding also proved crucial for lighting and heating systems
The science of electromagnetic phenomena is defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as elements of one phenomenon. The electromagnetic force is the one responsible for practically all the phenomena one encounters in daily life with the exception of gravity. Roughly speaking, all the forces involved in interactions between atoms can be explained by the electromagnetic force acting on the electrically charged atomic nuclei and electrons inside and around the atoms, together with how these particles carry momentum by their movement. This includes the forces we experience in "pushing" or "pulling" ordinary material objects.
The homopolar motor was one of the first (and simplest) electrical motors to be built. Its operation was demonstrated by Michael Faraday in 1821. Faraday went on to build two devices to produce what he called "electromagnetic rotation". One of these, now known as the homopolar motor, caused a continuous circular motion that was engendered by the circular magnetic force around a wire that extended into a pool of mercury wherein was placed a magnet. These experiments and inventions formed the foundation of modern electromagnetic technology.
The homopolar motor is driven by the Lorentz force: as it moves through a magnetic field, the conductor is pushed through a magnetic field by opposing forces. This force induces a torque around the axis of rotation which runs in the same direction of the electrical current.
Simplistically, the science behind electric motors is that if you have an electric current flowing through a wire that is in a magnetic field, it feels a force push on it. The homopolar motor is perhaps the easiest way to explain the resultant force from the interaction between a magnetic field and an electric current.
A motor needs two things to produce a rotational force. Current is provided by the battery, and runs through the screw, through the wire, and back through the top of the battery. Electrons run from the negative terminal (at the top) to the positive terminal, but for physics purposes, current is defined the opposite of this. Magnetic Field is the other component. The magnets dangling from the screw provide magnetic field. The north pole of the magnet is at the top, so the magnetic field points up. The direction of the resultant force created by the current and the magnetic field is perpendicular to both of the vectors. Since there are still two possible directions for force, the correct direction is the direction of the cross product of the vectors; . The result is a force directed toward me at the point where the wire touches the magnet. Since the force is on the edge, it spins the motor along an axis (which is perpendicular to the magnetic field in this situation).The motor (the screw and the magnet) spins remarkably quickly due to its size and low friction (it only makes contact with the stationary battery at the point of the screw).
They have two magnetic poles provided by the single permanent magnet that is used to produce the magnetic field, also required to generate rotational movement. It is called a homopolar motor because, unlike conventional DC motors, the polarity of the magnetic field emitted by the conductor and the permanent magnets does not change.
Questions & Answers:
Q: Does reversing the polarity of the battery have any effect on the motor?
A: Yes. For the first motor, by attaching the magnet and screw to the positive terminal the motor will rotate counterclockwise. The motor will rotate clockwise by attaching the magnet and screw to the negative terminal. Reversing the direction of the force can be manipulated switching the polarity contact point of the battery as well.
Q: Would this motor work with any type of magnet?
A: No. Household magnets like those found on your refrigerator will not work. The magnetic field must be strong enough to interact with the flow of electricity to cause the motor to spin. The stronger the magnet, the faster it will spin.
Q: Does changing the battery type have any effect on the motor?
A: Different batteries have differing current and voltage. In changing the type, the difference is found in the life of the battery and the rate at which the motor spins.
Q: Suppose the homopolar motor was spinning in the clockwise direction. What would happen if you used your finger to force it to spin in the anticlockwise direction?
A: The motor would momentarily slow down and even move counterclockwise if enough force is exerted. The motor would then resume rotating in the clockwise direction.
Applications to Everyday Life:
Electromagnetic lifting cranes are used to lift and transport steel scraps, sheets, medium and thick plates, and steel bars. They use electromagnetism to magnetize the coil for lifting and demagnetize the electromagnetic coil for dropping the materials in the required place. An electromagnetic container lifter works in the similar manner for transporting the container from the ship to port and vice versa.
Electromagnetic energy is a limitless source of power that is used in many industries across the United States. This technology runs several key instruments in modern automobiles, from electrical features, to whole ignition systems and engines (Prius, Tesla, Volt, etc.).
Cell phones operate with radio frequencies, a form of electromagnetic energy located on the electromagnetic spectrum between FM radio waves and the waves used in microwave ovens, radar, and satellite stations. Cell phones do not emit ionizing radiation, the type that damages DNA.
Photographs:
Videos:
Homopolar Motor:
Homopolar Roller:
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