Informal Learning Activity Yogurt Cup Speakers (en español)

Quick Look

Grade Level: Middle school

Time Required: 45 minutes

Expendable Cost: US $2.00

Group Size: 2

Subject Areas: Physical Science, Problem Solving, Reasoning and Proof, Science and Technology

Introduction
Bolded words are vocabulary and concepts to highlight with students during the activity.

The study of electromagnetism is the foundation of electrical engineering. In addition, it finds wide application in other engineering disciplines. Amazingly, electromagnets are used to make speakers! A sound is produced when a vibrating object moves the air particles around it, which in turn moves the air particles around them. A speaker takes an electrical signal and translates it into physical vibrations to create sound waves. Traditional speakers do this with an electromagnet and a permanent magnet: the electromagnet is under the influence of a constant magnetic field created by a permanent magnet. These two magnets interact with each other in the usual way: the positive end of the electromagnet is attracted to the negative pole of the permanent magnet and repelled by its positive pole. A stereo signal constantly reverses the flow of electricity, switching the north and south ends of the electromagnet. In this way, the alternating current constantly reverses the magnetic forces between the voice coil and the permanent magnet, rapidly pushing the coil back and forth. When the coil moves, it pushes and pulls on the speaker cone. This vibrates the air around the speaker and creates sound waves, which is what you hear!

A photograph shows a wire coil taped to the outside of a plastic yogurt cup. Insulation is removed from the two wire ends.
Figure 1. Set-up for a simple student-created speaker.
copyright
Copyright © 2005 Center for Engineering and Computing Education, University of South Carolina

Supplies

Each group needs:

  • 1 ~8 oz. plastic cup or yogurt cup container (emptied and rinsed)
  • 1 round magnet
  • wire, coated 20 gauge, 10 ft. (3 m)
  • electrical tape, 12" (30 cm)
  • C-cell battery
  • 3 paperclips
  • sandpaper

For the class to share:

  • radio/stereo with detachable speakers

Subscribe

Get the inside scoop on all things TeachEngineering such as new site features, curriculum updates, video releases, and more by signing up for our newsletter!
PS: We do not share personal information or emails with anyone.

Procedure

Procedures Overview

Student pairs build electromagnets, study their interactions with permanent magnets, and then use this knowledge to build working speakers.

Procedure

  1. Organize students into groups of two.
  2. Ask students if any of them know how and why speakers work. After some discussion, describe to them how they work (refer to the Introduction section).
  3. Explain to students the difference between electromagnets and permanent magnets.
  4. Inform groups that their challenge is to build an electromagnet and explore its properties through the creation of a speaker. Show them the available supplies.
  5. Hand out the supplies to the teams.

Making the Electromagnet

To make the electromagnets, have students proceed with the following steps. (Note: Work through each step with them.)

  1. Have students wind the wire around the C battery, leaving two inches hanging free at each end.
  2. Have them carefully remove the wire from the battery, preserving its coiled shape. If needed, secure it with a small piece of tape.
  3. Sand the enamel off of the wire on the two free ends, removing about an inch of insulation.
  4. Have students hold the wire so that each end of the wire touches the two ends of the battery—they now have an electromagnet.
  5. To understand its capabilities, instruct groups to put the electromagnet near the permanent magnet to see how it reacts.

Making and Testing a Speaker

Next, students make speakers using their electromagnets.

  1. Instruct students to tape the permanent magnet to the inside bottom of the yogurt container/plastic cup.
  2. Then, tape the electromagnet to the outside bottom of the cup (see Figure 1) so they are as close together as possible.
  3. Have students check that the permanent and electromagnets are secured to the cups with tape. Once confirmed, they are ready to test the speakers.
  4. One at a time, have groups test their speakers (see Figure 2). Attach one end of the free wires to each of the speaker wire connectors on the back of the radio. (Note: Use caution because the wires get very hot if the radio volume is turned to high for too long.)
    A photograph shows a yogurt cup speaker attached to the radio speaker plugs. Arrows point to where the two speaker wires are inserted in the speaker plugs.
    Figure 2. The yogurt cup speaker in action after it is hooked up to the radio/stereo.
    copyright
    Copyright © 2005 Center for Engineering and Computing Education, University of South Carolina

Wrap Up - Thought Questions

  • Why might an engineer use an electromagnet rather than a permanent magnet?
  • Would making more coils in your electromagnet change its power?

More Curriculum Like This

Upper Elementary Lesson
A Magnetic Personality

Students investigate the properties of magnets and how engineers use magnets in technology. Specifically, students learn about magnetic memory storage, which is the reading and writing of data information using magnets, such as in computer hard drives, zip disks and flash drives.

Upper Elementary Lesson
The Electric and Magnetic Personalities of Mr. Maxwell

Students are briefly introduced to Maxwell's equations and their significance to phenomena associated with electricity and magnetism. Basic concepts such as current, electricity and field lines are covered and reinforced. Through multiple topics and activities, students see how electricity and magne...

High School Lesson
Changing Fields

Students induce EMF in a coil of wire using magnetic fields. Students review the cross product with respect to magnetic force and introduce magnetic flux, Faraday's law of Induction, Lenz's law, eddy currents, motional EMF and Induced EMF.

Middle School Lesson
Riding the Radio Waves

Students learn how AM radios work through basic concepts about waves and magnetic fields. Then students learn general concepts about magnetic fields, leading into how radio waves are created and transmitted.

Copyright

© 2013 by Regents of the University of Colorado

Last modified: May 12, 2022

Free K-12 standards-aligned STEM curriculum for educators everywhere.
Find more at TeachEngineering.org