• Visit
    • Calendar
    • After Dark Thursdays
    • Buy Tickets
    • Exhibits
    • Museum Galleries
    • Artworks on View
    • Hours
    • Getting Here
    • Visitor FAQ
    • Event Rentals
    • Field Trips
  • Education
    • Professional Development Programs
    • Free Educator Workshops
    • 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
    • Donor & Corporate Member FAQ
    • Host Your Event
    • Volunteer
  • Store
  • Visit
    • Frequently Asked Questions
    • Calendar
      • Today
      • This Week
      • Online
      • After Dark Thursday Nights
      • Arts
      • Conferences
      • Cinema Arts
      • Free + Community Events
      • Fundraising Events
      • Kids + Families
      • Members
      • Special Hours
      • Private Event Closures
    • Prices
    • Hours
    • Getting Here
    • Museum Map
    • Free Admission and Reduced Admission
    • 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
        • Tactile Dome
          • 1971 Press Release
        • Black Box
        • Curator Statement
      • Gallery 2: Tinkering
        • Curator Statement
      • Bechtel Gallery 3: Seeing & Reflections
        • Curator Statement
      • Gordon and Betty Moore 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
    • Restaurant & Café
    • School Field Trips
      • Getting Here
        • Bus Routes for Field Trips and Other Groups
      • Admission and Tickets
      • Planning Guide
      • Reservations
        • Field Trip Request Form
      • Resources
    • Event Rentals
      • Full Facility & Gallery Bundles
      • Fisher Bay Observatory Gallery & Terrace
      • Moore East Gallery
      • Bechtel Central Gallery & Outdoor Gallery
      • Osher West Gallery
      • Kanbar Forum

      • Weddings
      • Proms and School Events
      • Daytime Meetings, Events, & Filmings
      • Happy Hour on the Water

      • Rentals FAQ
      • Event Planning Resources
      • Rental Request Form
      • Download Brochure (pdf)
    • Groups / Tour Operators
      • Group Visit Request Form
    • Exploratorium Store
    • Contact Us
  • Education
    • Black Teachers and Students Matter
    • Professional Development Programs
      • Free Educator Workshops
      • Professional Learning Partnerships
      • 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?
        • Watch and Do Science
        • 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
      • Cambio
    • Tools for Teaching and Learning
      • Learning Toolbox
      • Science Snacks
      • Digital Teaching Boxes
      • Science Activities
      • Tinkering Projects
      • Recursos gratuitos para aprender ciencias
      • 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
        • Spectrum
          • Arts
          • Behind the Scenes
          • News
          • Education
          • Community & Collaborations
          • Science
        • Eclipse
        • Studio for Public Spaces
        • Tangents
        • Resonance See & Hear Blog
        • Fabricated Realities
        • Tinkering Studio: Sketchpad
        • Exploratorium on Tumblr
      • Exhibits
      • Video
      • Websites
      • Apps
        • Total Solar Eclipse
  • About Us
    • Our Story
    • Land Acknowledgment
    • Explore Our Reach
    • Impact Report
    • Awards
    • Our History
      • 50 Years 1969–2019

    • Leadership Cabinet
    • Board of Trustees
    • Board of Trustees Alumni
    • Staff Scientists
    • Staff Artists

    • 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
    • Teacher Institute
    • Institute for Inquiry
    • Explainer Programs
    • Studio for Public Spaces
    • Exhibit Making
    • Partnerships
      • Building Global Connections
        • Global Collaborations
          • Projects
          • Approach
          • People
          • Impact
      • Partnering with Science Agencies
        • NASA
        • NOAA
      • Partnering with Educational Institutions
      • Osher Fellows

    • Job Opportunities
    • Become a Volunteer

    • Contact Info
    • Newsletter
    • Educator Newsletter
    • Blogs
    • Follow & Share
    • Press Office

    • FY21 Audit Report
    • 990 FY20 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
    • Donor & Corporate Member FAQ
    • Volunteer
      • How to Apply
      • Application for Internships
      • Our Contract
      • Application for Individuals
  • Press Office
    • Press Releases
    • News Coverage
    • Events Calendar
    • Photographs
    • Press Video
    • Press Kits
    • Press Visits
    • Exploratorium Logos
    • Recent Awards
    • Praise for the Exploratorium
    • Join Our Press List
  • Store

Masks and vaccinations are recommended. Plan your visit  

Visitor FAQ Buy Tickets Donate Today
Exploratorium
Exploratorium
  • Visit
    • Calendar
    • After Dark Thursdays
    • Buy Tickets
    • Exhibits
    • Museum Galleries
    • Artworks on View
    • Hours
    • Getting Here
    • Visitor FAQ
    • Event Rentals
    • Field Trips
  • Education
    • Professional Development Programs
    • Free Educator Workshops
    • 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
    • Donor & Corporate Member FAQ
    • Host Your Event
    • Volunteer
  • Store
Science Snacks
Science activity that demonstrates light interference in soap

Soap Film on a Can

What light through yonder film can breaks?

Why do we see colors in oily water and soap bubbles? Sometimes we see red, sometimes blue, and sometimes it appears as though we see nothing at all. Experiment with soap film to observe the behavior and colorful appearance of different wavelengths of light. 


Grade Bands: 
3-5
6-8
9-12
Subject: 
Perception
Light, Color & Seeing
Physics
Light
Waves
Keywords: 
wavelength
interference
soap
bubbles
reflections
color
video
NGSS and EP&Cs: 
PS
PS4
CCCs
Patterns
Scale, Proportion, and Quantity
Structure and Function
Stability and Change

  • Facebook logo
  • Reddit logo
  • Twitter logo


Video Demonstration

Soap Film on a Can: Introduction
Soap Film on a Can: Materials and assembly
Soap Film on a Can: Do the experiment
Soap Film on a Can: What's going on

Tools and Materials

  • One black plastic film can (see video for instructions on how to make a substitute black canister)
  • Dishwashing liquid—Dawn™ Ultra Original Scent in blue works best
  • Water—distilled water works best
  • Mixing container
  • A shallow dish to hold the soap solution
  • White paper
  • A pencil or pen

Assembly

  1. To make the soap solution, mix 1 part dishwashing liquid in 10 parts water. Tip: Soap films work best and last longer if you let them sit overnight, allowing the soap molecules to diffuse through the entire solution.
  2. Pour the soap solution into the shallow dish, filling it to approximately 1/2 inch (1 centimeter) deep. 
  3. Remove the lid from the film can.
  4. Place the white paper on a tabletop. The white paper is important because light will then scatter up off the paper, bouncing off the soap film and into your eye.

To Do and Notice

Dip the open mouth of the film can straight down into the soap solution. When you pull it out, a soap film should have formed over the opening of the can.

Rotate the can so that the soap film is in a vertical plane. Hold it over the white paper in a brightly lit place.

You will see colors form and move around on the soap film. Over time, you might notice horizontal bands of color forming.

After a while, the top of the soap film becomes invisible because the soap film becomes thinner than a wavelength of light—under 300 nanometers thick. Even though you can’t see it, the soap film is still there! You can test this by poking a pencil point into the invisible region of the soap film—it will break.


What’s Going On?

Think of the soap film as a water sandwich: a layer of water held between two layers of soap molecules. When the soap film is vertical, gravity pulls the water down, causing the top of the film to become thinner and the bottom to become thicker.

The reflections caused by these different thicknesses of soap film then cancel out different colors, producing bands of color that stretch across the film can.

Light reflects from both the front and back of the soap film. The light waves reflected from the front of the soap film are inverted while those from the back are not. The two reflections combine, producing interference of light.

When interference of light occurs, some color wavelengths add up “out of phase”—the highest point of one wave lines up with the lowest point of the other—and are therefore canceled. Others add up “in phase”—where the highest point of one wave lines up with the highest point of the other—and are therefore strengthened.

Understanding the colors of the soap film from top to bottom:

When soap films are thin compared to the wavelengths of light moving through them, they reflect no light at all, making them invisible. You can see this happening at the top of your soap film. Poking the invisible soap film with a pencil point reveals its presence because the entire soap film breaks.

When the soap film is a quarter of a wavelength of blue light thick, blue light is reflected strongly. At this same point, the film is about an eighth of a wavelength of red light thick—the wavelength of red light is just under twice that of blue, so some red light is reflected. The result is that the transparent film thickens into a metallic white sheen that appears bluer as it gets thicker.

Moving down the film, when it is half of a wavelength of blue light thick, the blue waves add up out of phase and cancel. At this point, the soap film is now a quarter of a wavelength of red light thick and the red waves add up in phase, resulting in a reddish color band.

Every integer multiple of a half blue wavelength in thickness, blue light is canceled; every odd multiple of a quarter blue wavelength, blue light is strengthened. Every multiple of a half red wavelength, the red light is cancelled. The result is alternating bands of bluish and reddish light as the film grows thicker—like contour lines on a topographic map.


Going Further

To further understand how wavelengths move through soap films and to observe how sine waves add up or cancel out, try making our Soap-Film Interference Model.

Robert Hooke first reported observing the transparent film in a letter to the Royal Society. His letter indicates that he thought the film actually did not exist where it was transparent, but that some force held the colored film in place. A simple experiment of poking the invisible film and breaking it proves the existence of the invisible film.

To further experiment with soap films, try drilling a small hole (approximately 5 mm in diameter) in the bottom of the film can. Create a soap film over the open mouth of the can and then blow through the hole. The soap film will bulge out into a dome.

Here’s another cool trick: Try blowing into the can to create a dome and then plug the hole with your finger. If you orient the film can with the opening facing up, colored rings will appear in the soap film.

Our understanding of the phenomenon explored in this Science Snack is built on the work of many scientists.

Highlighted Scientist: Dr. Nergis Malvalvala

Dr. Nergis Malvalvala is a Pakistani physicist who was one of the first scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) to observe gravitational waves, the disturbances in the curvature of space-time caused by accelerating objects like neutron stars and black holes. Dr. Mavalvala is a pioneer in developing instrumentation that can detect very small changes in the interference patterns of light, and was awarded a MacArthur Fellowship—a prize to recognize individuals who have shown “extraordinary originality and dedication in their creative pursuits and a marked capacity for self-direction"—in 2010. In the Soap Film on a Can Science Snack, you can explore the interference of light with itself through a thin film, and learn a bit how light can cancel itself out—similar to how Dr. Mavalvala studies light in the giant LIGO systems.


Resources

For more information, read Soap Bubbles: Their Colors and Forces Which Mold Them by C.V. Boys (Dover Publications, 2012). 



Related Snacks

Science activity that models light wave interference
Soap Film Interference Model

Model the behavior of light reflecting off soap film surfaces.

Science activity that uses gravity to turn soap film into an ever-shifting array of colors
Soap Film Painting

Gravity turns soap film into an ever-shifting, colorful masterpiece.

Science activity that demonstrates wave interference
On the Fringe (formerly Bridge Light)

Air trapped between two pieces of clear plastic produces rainbow-colored interference patterns.



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
  • Calendar
  • Buy Tickets
  • Getting Here
  • Store
  • Event Rentals
  • About Us
  • Become a Member
  • Donate
  • Jobs
  • Volunteer
  • Press Office
  • Land Acknowledgment

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

The Exploratorium is a 501(c)(3) nonprofit organization. Our tax ID #: 94-1696494
© 2023 Exploratorium | Terms of Service | Privacy Policy | Your California Privacy Rights |