Posts Tagged ‘Interference’

Bubbles and Interference

This week, you shall be entertained with the physics of soap bubbles! Soap-bubble rainbows are caused by thin-film interference. When a light ray strikes the film of of soap bubble, some of the light reflects off of the film’s top surface (Ray 1). Other rays (Ray 2), however, pass into the film, reflect off of the bottom surface of the bubble, and passes back through the film.


Ray 1 changes phase 180° as it reflects (which only happens when light reflects off a material with a higher index of refraction than the medium it is traveling in), and Ray 2 does not change phase as it reflects but it travels an extra distance through the film. This results in a path length difference of about 2x the thickness of the film.

So you end up with the two different rays being either in phase with each other (constructive interference), completely out of phase (destructive interference), or somewhere in between. The path length difference at a certain point on a soap bubble might cause destructive interference for blue light, but constructive interference for red light. You’ll end up seeing red at that spot.


When you wash your hands today, take a moment to bask in the loveliness of soap bubbles! ^ ^


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Ahh…this will be a pretty random and incoherent post.  All of that turkey in my system is making me sleeepy. : ]

So during the Black Friday rush, my dad got me a Jabra Bluetooth Headset.  After playing around with it, I started wondering about how this wireless connection is formed in the first place, allowing me to “control” my cell phone/computer/etc. from a distance.  It turns out that data is transmitted via low-power radio waves at a frequency of 2.45 gigahertz. Bluetooth devices send out pretty weak signals of only 1 milliwatt, avoiding interference with other systems like your TV or telephone (we wouldn’t want that happening!)  The low power also explains why the operating range is only up to 33 feet.

I Have a Blue Tooth From Eating Mint Chocolate! xD

Another item of interest to me was how a single Bluetooth headset could connect to several devices at once and still function normally.  One might expect all of those emitted waves in that little bubble with a 33 ft radius to interfere with each other.  However, Blue uses a spread-spectrum frequency hopping technique to minimize such a possibility.  Basically, the device “hops” between 79 randomly selected frequencies in a certain range 1,600 times a second!!  So it is very very unlikely for two devices to have the same frequency at the same time, preventing creation of a new wave pattern from two or more waves.

Hope everyone had a nice Thanksgiving!!  If you have some spare time, why not start getting into the holiday spirit and spice up those carols with a bit of physics knowledge? 😀

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