PHYS 1407 – Conceptual Physics II

Interference Colors

Leader: ___________________ Recorder: __________________________

Skeptic: ___________________ Encourager: ________________________

Material

Plastic Vial

Dish of soapy water

Introduction

Thin films of water often produce beautiful patterns of colors due to thin film interference effects. In this activity, we will explore the colors produced in soap films which are thin films of water encased in outer layers of soap.

Procedure

Place the open end of the vial into the container of soapy water so that a soap film will appear at the end.

Hold the soap bubble so that if faces you. Tilting the container up at a slight angle can help you to see the film.

The appearance of the soap film will change over time.

Q1. Describe the appearance of the soap film initially.

Q2. Describe how the appearance of the soap film changes over time.

The soap film also varies from top to bottom.

Q3. Describe how the soap film changes from top to bottom.

Q4. Since the film is oriented vertically, what will happen to the water in the film over time?

Q5. What effect will this have on the thickness of the film? In particular will it be uniform in thickness or will the thickness vary from top to bottom?

Q6. If the thickness varies form top to bottom, where will it be thicker?

Q7. Sketch a diagram showing the thickness of the film from top to bottom.

The minimum thickness of the film that will destructively interfere a particular color of light is approximately the wavelength of light divided by 10.

Q8. Will a thinner or thicker section of the film destructively interfere blue light? Explain.

Q9. If blue light is removed from white light, what color will the light appear?

Q10. Of the primary colors red, green, and blue which will be the next to destructively interfere?

Q11. If that color light is removed, what will be the next color light to appear?

Q12. Of the primary colors red, green, and blue which will be the next to destructively interfere?

Q13. If that color light is removed, what will be the next color light to appear?

Q14. So from top to bottom, what should be the order of the colors of light?

Q15. Does your answer to q14 agree with your observation of the soap film? If not, determine the source of any discrepancy.