Activity 7

Introduction

Just a little soapy water and a ring through which to blow the soap film is all you need. Even on the soapy film you can see the patterns and colors change. Then as the bubbles float in the air, we can see colors swirling and swimming across the almost perfectly spherical surface. Why do we see these colors and why do they change? We may have seen similar patterns and colors on an oil slick on the road. How in the world could such ugly stuff as motor oil be so colorful? In this activity we'll examine this strange phenomenon and how we can experience it throughout nature. We'll also examine what thin slits do to light and how this phenomenon is similar to that of bubbles and oil slicks.

Not all colors are caused by interference effects. The red color seen when white light illuminates a red object is due to absorption and reflection. The colot does not change when you change your view.

Procedure: Bubbles

• Gather these items from your home or workplace:
  • liquid detergent or glycerine
  • a metal ring through which to blow bubbles
  • two small glass slides

• Use the soap and ring to blow bubbles (preferably outside -- sunlight works best). What do you notice about the colors and patterns on the surface of the bubbles?

• Estimate the thickness of the soap bubble film. If there is 1/2 mm³ of soap in a bubble of 5 cm radius (Volume = 4Πr²d)
  
• How thick isthe soap bubble compared to the wavelength of visible light?

• Are the colors and patterns from the slides similar to those on the bubbles? Think of how these two seemingly very different experiments can yield very similar phenomena.