LAB 12 Thin Films

Physics Lab 12 June 28, 2010 Name __________________


I. Title: Thin Films

II. Purpose: to observe the effects of thin films on destructive interference of light, and to determine the mass of an average bubble

III. Equipment: Soapy fluid (source of bubbles) - individual bottles of bubbles; a wand to make the bubbles; a blower; a digital scale; stopwatch

IV. Procedure:
1. Have a lab partner acquire the stuff needed.
2. Weigh an individual closed bottle of bubbles, with wand inside, in grams. Record.
3. Choose a lab partner to be the “blower.”
4. Have the “blower” carefully remove the “wand” to extract fluid, then have the blower create bubbles by blowing; don’t drop fluid onto floor or table, as that will create personal error
5. While the blower is “blowing,” have another partner count the number of bubbles. Have yet another partner determine how long it takes for an average bubble to exist before popping. Finally, have an additional person note the different colors on the bubble’s “skin” as it slowly vanishes.
6. Blow about 100 bubbles. Do not confuse your group’s bubbles with bubbles blown by other blowers in other groups.
7. As the bubbles are being created and counted, carefully observe a number of bubbles as they become invisible at the top before they pop. Record observations. This will be an example of thin film destructive interference.
8. When completed, return the wand to the bottle and seal the bottle.
9. Weigh the cylinder again in grams. Record.
10. Subtract the weight of the bottle in #9 from the weight of the bottle in #2. Record. (This is the mass of the fluid used to make bubbles).
11. Calculate the average mass of a bubble by dividing the mass you found in #10 by 100 (or as many bubbles as you counted). Record.

V. Data, observations, calculations:
1. Mass of sealed bubble bottle: ________ grams

2. Number of bubbles blown: _________

3. Mass of bottle after bubbles are blown:_____ g

4. Mass of soapy fluid used: _______ g

5. Average mass of a bubble: _______ g

6. Observations of the thin films:
a. Colors
b. “life” of a bubble: _______ seconds
c. invisibility

VI. Results: As ever, re-read the purpose (Section II) and determine if you achieved this purpose, and how well you achieved it, i.e., what are your conclusions?

VII. Error:

Quantitative: NA
Qualitative:
1. Personal – what did you or your partner(s) do to screw up?
2. Systematic – any equipment failures or violent thunderstorms in the lab while doing this experiment?
3. Random – always random error, unless you do multiple trials and then take an average …

VIII. Questions:
1. How much time did the average bubble last before it broke?
2. What colors did you notice in the bubbles?
3. Why did some of the bubbles rise in the air, rather than fall?
4. How would this lab be different if the room temperature were much colder?