Engineering Speakers

Science background gives teachers more in-depth information on the phenomena students explore. Here is an excerpt from the science background section on engineering speakers.

Electromagnets and Circuits

Electrons can move more easily through some materials than others. Electric conductors are materials that allow electrons to pass through them easily. Metals such as copper and aluminum are electric conductors because they have electrons that are loosely held and therefore can easily be pushed from their shells by an outside force.

Electric insulators are materials that do not allow electrons to pass through easily. Rubber and plastic are both good electric insulators. This is why electrical cords are covered in rubber or plastic. The electricity cannot travel through the rubber or plastic and is forced to follow the path on the aluminum or copper wires. Some materials are semiconductors, which means they can sometimes act as a conductor, depending on what other molecules are around.

Because electromagnets are made with electricity, they can be demagnetized when the electricity is turned off. This is possible because electromagnets form a circuit, which is the circular path that electrons travel in a negative to positive direction.

All circuits have the same basic parts, including an energy source such as a battery. The battery has stored chemical energy that converts to electrical energy. This energy provides the input of force that pushes the electrons in the conductive material through the circuit. an open circuit

Circuits also have wires, which are the paths that electrons travel in the circuit. Energy moves from the battery through the conductive wires. The wires in a circuit are attached to an object that can convert electrical energy to do work (any change in position, speed, or state of matter due to force). All circuits must include something that can do work. Without this part, the electricity will cause a short circuit by overheating the circuit.

For example, a light bulb is an object that does work. When electrons reach the light bulb in a circuit, they transfer electrical energy. The light bulb changes the electrical energy into outputs of light energy and heat. In a perfect system, the same amount of energy that was transferred through the circuit would be available to light up the bulb because of the conservation of energy. However, in the real world, some of the energy transfers out of the system due to resistance, which is the force opposing the current. The electrons then continue on their path. They return to the opposite side of the battery.

Circuits also have switches to open and close the circuit. Electrons flow when a circuit is closed. This is “on.” A closed circuit will cause the light bulb to light up. Electrons cannot flow when a circuit is open. This is “off.” No work can be done in an open circuit.

The way a circuit is put together affects the amount of electric current that can do work. Current is a measure of the rate that electric charge passes through a point in an electric circuit over time. The amount of work that can be done increases as current increases. For example, a fast current will cause a light bulb to shine more brightly than a slow current. This is because more electrons reach the bulb in the same amount of time. The ampere (A) is a unit of measure of electric current.

Electric current produces a magnetic field. As electrons in a conductor move in the same direction as one another, their movement produces a magnetic field around the wire conductor. The magnetic field around a straight wire is not very strong, but if the wire is wrapped in a coil, the fields produced in each turn of the coil add up to create a stronger magnetic field. This is the idea behind an electromagnet: a tightly coiled wire produces a magnetic field when electricity passes through the wire. The electromagnet becomes magnetized when the circuit is closed and demagnetized when the circuit is open.

Parts of a Speaker

The electromagnet in a speaker is attached to a cone that is made of fabric, plastic, paper or lightweight metal. The purpose of the cone is to push air so that it vibrates, producing sound. Sound is energy that is carried in waves of vibrating molecules. As forces transfer energy through a system, they disturb molecules at rest, causing them to vibrate. As energy is carried in waves of vibrating molecules, it produces sound.

On the other side of the electromagnet is a permanent magnet. When the speaker is connected to a receiver, electricity flows through the wires. If the electromagnet in a speaker is positioned so that its north pole is near the north pole of the permanent magnet, the two magnets will repel each other, and be attracted to each other’s south pole. These attracting and repelling forces cause the coil to move back and forth, pulling and pushing the speaker cone. As the cone moves back and forth, it produces vibrations.

The volume of a speaker can be changed. A stronger electromagnet will cause the cone to move more, generating a louder noise. This is similar to banging a drum harder, making the drum membrane vibrate more so it produces a louder sound. There are several ways to make the electromagnet stronger. One way is to increase the number of coils an electromagnet has so that it produces a stronger magnetic field. Another way is to increase the electrical current that flows through the circuit. The size of the cone will also change how much air is vibrating, which will affect the speaker’s sound.