• Visit
    • Buy Tickets
    • Calendar
    • After Dark Thursdays
    • Exhibits
    • Artworks on View
    • Getting Here
    • Event Rentals
  • Education
    • Professional Development Programs
    • Tools for Teaching and Learning
    • Learning About Learning
    • Community Programs
    • Educator Newsletter
  • Explore
    • Browse by Subject
    • Activities
    • Video
    • Exhibits
    • Apps
    • Blogs
    • Websites
  • About Us
    • Our Story
    • Partnerships
    • Global Collaborations
    • Explore Our Reach
    • Arts at the Exploratorium
    • Contact Us
  • Join + Support
    • Donate today!
    • Membership
    • Join our donor community
    • Engage your business
    • Attend a fundraiser
    • Explore our reach
    • Thank you to our supporters
    • Host your event
    • Volunteer
  • Store
  • Visit
    • Buy Tickets
    • Frequently Asked Questions
    • Calendar
      • Today
      • This Week
      • After Dark Thursday Nights
      • Arts
      • Conferences
      • Cinema Arts
      • Free and Community Events
      • Fundraising Events
      • Kids + Families
      • Live Webcasts
      • Members
      • Ongoing + Series
      • Special Hours and Open Mondays
      • Private Event Closures
    • Hours
    • Getting Here
    • Museum Map
    • Reduced Rates & Community Day
    • Accessibility
    • Tips for Visiting with Kids
    • How to Exploratorium
    • Exhibits
    • Tactile Dome
    • Artworks on View
    • Cinema Arts
    • Kanbar Forum
    • Black Box
    • Museum Galleries
      • Bernard and Barbro Osher Gallery 1: Human Phenomena
        • Exhibition: Science of Sharing
          • Educator Activities
        • Tactile Dome
          • 1971 Press Release
        • Black Box
        • Curator Statement
      • Gallery 2: Tinkering
        • Curator Statement
      • Bechtel Gallery 3: Seeing and Listening
        • Curator Statement
      • Gallery 4: Living Systems
        • Curator Statement
      • Gallery 5: Outdoor Exhibits
        • Curator Statement
      • Fisher Bay Observatory Gallery 6: Observing Landscapes
        • Wired Pier Environmental Field Station
        • Curator Statement
      • PlayLists
        • All PlayLists
        • A Different Light
        • “We” or “Just Me”?
        • See Yourself in Cells
        • Greatest Hits: Gallery 2
        • Greatest Hits: Gallery 3
        • Greatest Hits: Gallery 4
        • Museum Map
    • Restaurant & Café
    • School Field Trips
      • Getting Here
        • Bus Routes for Field Trips and Other Groups
      • Prices and Discounts
      • Planning Guide
      • Reservations
        • Field Trip Request Form
      • Resources
    • Groups / Tour Operators
      • Group Visit Request Form
    • Event Rentals
      • COVID-Compliant Options
      • Full Facility & Gallery Bundles
      • Fisher Bay Observatory Gallery & Terrace
      • East Gallery
      • Bechtel Central Gallery
      • Osher West Gallery
      • Kanbar Forum
      • Weddings
      • Proms and School Events
      • Daytime Meeting & Event Options
      • Happy Hour on the Water
      • Rentals FAQ
      • Event Planning Resources
      • Rental Request Form
      • Download Brochure (pdf)
    • Exploratorium Store
    • Contact Us
    • Español
    • 繁體中文
    • 简体中文
    • 한국어
    • Français
    • Deutsch
    • Português
    • 日本語
  • Education
    • Professional Development Programs
      • Teacher Institute
        • About the Teacher Institute
        • Summer Institute for Teachers
        • Teacher Induction Program
        • Leadership Program
        • Teacher Institute Research
        • CA NGSS STEM Conferences
          • NGSS STEM Conference 2020
        • Science Snacks
          • Browse by Subject
          • Special Collections
          • Science Snacks A-Z
          • NGSS Planning Tools
          • Frequently Asked Questions
        • Digital Teaching Boxes
        • Meet the Teacher Institute Staff
        • Resources for Supporting Science Teachers
      • Institute for Inquiry
        • What Is Inquiry?
        • Inquiry-based Science and English Language Development
          • Educators Guide
            • Conceptual Overview
              • Science Talk
              • Science Writing
            • Classroom Video Gallery
              • Magnet Investigation
              • Snail Investigation
            • Teacher Professional Development
            • Project Studies
            • Acknowledgments
          • Conference: Exploring Science and English Language Development
            • Interviews with Participants
            • Plenary Sessions
            • Synthesis, Documentation, and Resources
        • Workshops
          • Participant Portal
          • Fundamentals of Inquiry
            • Summary Schedule
          • BaySci Science Champions Academy
          • Facilitators Guides
          • Commissioned Workshops
        • Resource Library
        • Meet the IFI Staff
      • Resources for California Educators
      • K-12 Science Leader Network
      • Resources for Supporting Science Teachers
      • Field Trip Explainer Program
    • Tools for Teaching and Learning
      • Learning Toolbox
      • Science Snacks
      • Digital Teaching Boxes
      • Science Activities
      • Tinkering Projects
      • Videos
      • Exhibits
      • Publications
      • Apps
      • Educator Newsletter
      • Exploratorium Websites
    • Educator Newsletter
    • Advancing Ideas about Learning
      • Visitor Research and Evaluation
        • What we do
        • Reports & Publications
        • Projects
        • Who we are
      • Center for Informal Learning in Schools
    • Community Programs
      • High School Explainer Program
      • Xtech
      • Community Educational Engagement
      • California Tinkering Afterschool Network
        • About
        • Partners
        • Resources
        • News & Updates
        • Further Reading
  • Explore
    • Browse by Subject
      • Arts
      • Astronomy & Space Sciences
        • Planetary Science
        • Space Exploration
      • Biology
        • Anatomy & Physiology
        • Ecology
        • Evolution
        • Genetics
        • Molecular & Cellular Biology
        • Neuroscience
      • Chemistry
        • Combining Matter
        • Food & Cooking
        • Materials & Matter
        • States of Matter
      • Data
        • Data Collection & Analysis
        • Modeling & Simulations
        • Visualization
      • Earth Science
        • Atmosphere
        • Geology
        • Oceans & Water
      • Engineering & Technology
        • Design & Tinkering
        • Real-World Problems & Solutions
      • Environmental Science
        • Global Systems & Cycles
        • Human Impacts
      • History
      • Mathematics
      • Nature of Science
        • Measurement
        • Science as a Process
        • Size & Scale
        • Time
      • Perception
        • Light, Color & Seeing
        • Listening & Hearing
        • Optical Illusions
        • Scent, Smell & Taste
        • Tactile & Touch
      • Physics
        • Electricity & Magnetism
        • Energy
        • Heat & Temperature
        • Light
        • Mechanics
        • Quantum
        • Sound
        • Waves
      • Social Science
        • Culture
        • Language
        • Psychology
        • Sociology
    • Browse by Content Type
      • Activities
      • Blogs
      • Exhibits
      • Video
      • Websites
      • Apps
        • Total Solar Eclipse
  • About Us
    • Contact Info
    • Our Story
    • Our History
      • 50 Years 1969–2019
    • Fact Sheet
    • Impact Report
    • Awards
    • Arts at the Exploratorium
      • Artworks on View
      • Artist-in-Residence Program
      • Cinema Arts
        • History and Collection
        • Cinema Artists-in-Residence
        • Resources and Collaborating Organizations
        • Kanbar Forum
      • Center for Art & Inquiry
        • Begin Here
          • Lessons
            • Bob Miller/Light Walk
            • Ruth Asawa/Milk Carton Sculpture
          • Workshops
      • Resonance
        • About the Series
        • See & Hear
        • Past Seasons
      • Over the Water
      • Black Box
      • Upcoming Events
      • Temporary Exhibitions
      • Arts Program Staff
      • Arts Committee and Advisers
    • Newsletter
    • Educator Newsletter
    • Press Office
    • Senior Leadership
    • Board of Trustees
    • Board of Trustees Alumni
    • Staff Scientists
    • Staff Artists
    • Partnerships
      • Building Global Connections
        • Global Collaborations
          • Projects
          • Approach
          • People
          • Impact
      • Partnering with Science Agencies
        • NASA
        • NOAA
      • Partnering with Educational Institutions
      • Osher Fellows
    • Exhibit Making
    • Institute for Inquiry
    • Teacher Institute
    • Online Engagement
    • Explainer Programs
    • Studio for Public Spaces
    • Job Opportunities
    • Become a Volunteer
    • Follow & Share
    • FY20 Audit Report
    • 990 FY19 Tax Return
    • Use Policy
      • Privacy Policy
      • Intellectual Property Policy
  • Join + Support
    • Donate today!
    • Membership
      • Membership FAQ
      • Member Benefits
      • After Dark Membership
      • Member Events
      • May Is for Members
    • Join our donor community
    • Engage your business
      • Corporate Membership
      • Luminary Partnerships
    • Attend a fundraiser
      • Wonder Funday
      • Science of Cocktails
      • Party at the Piers
        • Event Leadership and Host Committee
    • Explore our reach
    • Thank you to our supporters
    • Volunteer
      • Benefits
      • How to Apply
      • Application for Corporate Groups
      • Application for Internships
      • Application for Professional Societies
      • Application for School Groups & Clubs
      • Our Contract
      • Application for Individuals
      • Opportunities
  • Press Office
    • Press Releases
    • News Coverage
    • Events Calendar
    • Fact Sheet
    • Photographs
    • Press Video
    • Press Kits
    • Press Visits
    • Exploratorium Logos
    • Recent Awards
    • Praise for the Exploratorium
    • Join Our Press List
  • Store
 

Learn with us online while the Exploratorium is temporarily closed. You can help us reopen—donate today.

Exploratorium
Exploratorium
  • Visit
    • Buy Tickets
    • Calendar
    • After Dark Thursdays
    • Exhibits
    • Artworks on View
    • Getting Here
    • Event Rentals
  • Education
    • Professional Development Programs
    • Tools for Teaching and Learning
    • Learning About Learning
    • Community Programs
    • Educator Newsletter
  • Explore
    • Browse by Subject
    • Activities
    • Video
    • Exhibits
    • Apps
    • Blogs
    • Websites
  • About Us
    • Our Story
    • Partnerships
    • Global Collaborations
    • Explore Our Reach
    • Arts at the Exploratorium
    • Contact Us
  • Join + Support
    • Donate today!
    • Membership
    • Join our donor community
    • Engage your business
    • Attend a fundraiser
    • Explore our reach
    • Thank you to our supporters
    • Host your event
    • Volunteer
  • Store
Science Snacks
Science activity that demonstrates the eddy current phenomenon

Eddy Currents

A magnet falls more slowly through a metallic tube than it does through a nonmetallic tube.

When a magnet is dropped down a metallic tube, the changing magnetic field created by the falling magnet pushes electrons around in circular, eddy-like currents. These eddy currents have their own magnetic field that opposes the fall of the magnet. The magnet falls dramatically slower than it does in ordinary free fall inside a nonmetallic tube.


Grade Bands: 
6-8
9-12
Subject: 
Chemistry
Materials & Matter
Physics
Electricity & Magnetism
Keywords: 
eddy currents
magnetic field
exhibit-based
NGSS and EP&Cs: 
PS
PS1
PS2
CCCs
Cause and Effect

  • Facebook logo
  • Reddit logo
  • Twitter logo


Tools and Materials

  • One two- or three-foot (60-centimeter or one-meter) length of aluminum, copper, or brass tubing (do not use iron!) with an inner diameter larger than the magnet and with walls as thick as possible
  • A neodymium disk ­magnet at least 1/2 inch (1.25 cm) in diameter and longer than its diameter (you can stack several magnets together to get the right length)
  • A nonmagnetic object, such as a plastic-­barreled pen or a wooden pencil
  • One 3-foot (1 m) length of PVC or other non­metallic tubing
  • Optional: Two thick, flat pieces of aluminum (available at hardware and home-improvement stores), cardboard, masking tape, rubber bands or cord

Assembly

None needed.


To Do and Notice

Hold the metal tube vertically above a table and drop the magnet through the tube. Then drop a nonmagnetic object, such as a pen or pencil, through the tube. Notice that the magnet takes noticeably more time to fall. Now try dropping both magnetic and nonmagnetic objects through the PVC tube.

In addition to dropping these objects through the tubes, a simple, visible, and dramatic demonstration can be done by merely dropping the magnet between two thick, flat pieces of aluminum. The aluminum pieces should be spaced just slightly farther apart than the thickness of the magnet. A permanent spacer can easily be made with cardboard and masking tape if you don’t want to hold the pieces apart each time. Rubber bands or cord can hold the pieces all together. The flat surfaces need to be only slightly wider than the width of the magnet itself. Thickness, however, is important. The effect will be seen even with thin pieces of aluminum, but a thickness of about 1/4 inch (6 mm) will produce a remarkably slow rate of fall. Allow at least a 6-inch (15-cm) fall. (See the diagrams below; click to enlarge.)


What’s Going On?

As the magnet falls, the magnetic field around it constantly changes position. As the magnet passes through a given portion of the metal tube, this portion of the tube experiences a changing magnetic field, which induces the flow of eddy currents in an electrical conductor, such as the copper or aluminum tubing. The eddy currents create a magnetic field that exerts a force on the falling magnet. The force opposes the magnet’s fall. As a result of this magnetic repulsion, the magnet falls much more slowly.


Going Further

Eddy currents are often generated in transformers, leading to power losses. To combat this, thin laminated strips of metal are used in the construction of power transformers, rather than making the transformer out of one solid piece of metal. The thin strips are separated by insulating glue, which confines the eddy currents to the strips. This reduces the eddy currents, thus reducing the power loss.

With high-strength neodymium magnets, the effects of eddy currents become even more dramatic. These magnets are available from many scientific supply companies and the price is relatively affordable.

Eddy currents are also used to dampen unwanted oscillations in many mechanical balances. If you have access to a balance, look to see if there is a thin metal strip that moves between two magnets.



Related Snacks

Science activity demonstrating that magnets can affect things that aren’t magnetic
Mind the Magnetic Gap

Magnets can affect things that aren’t magnetic.


Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Attribution: Exploratorium Teacher Institute

  • Education
    • Teacher Institute
    • Tools for Teaching and Learning
      • Science Snacks
        • Browse by Subject
        • Special Collections
        • Science Snacks A-Z
        • NGSS Planning Tools
        • Frequently Asked Questions

Connect with us!

  •   Sign up for our educator newsletter
  •   Follow #ExploEDU
  •   Teacher Institute YouTube
  •   Teacher Institute Facebook
  •  teacherinstitute @exploratorium.edu
Exploratorium
Visit
Join
Give

Pier 15
(Embarcadero at Green Street)
San Francisco, CA 94111
(415) 528-4444

Contact Us

  • Plan Your Visit
  • Buy Tickets
  • Hours
  • Getting Here
  • Calendar
  • Tactile Dome
  • Store
  • About Us
  • Become a Member
  • Donate
  • Event Rentals
  • Jobs
  • Volunteer
  • Press Office

Get at-home activities and learning tools delivered straight to your inbox

© 2020 Exploratorium | Terms of Service | Privacy Policy | Your California Privacy Rights |