The Essence of Wonder

True wonder arises from delving deeper into the essence of things, which is the fundamental purpose of science. While it may sometimes demystify a phenomenon, revealing it as mundane, it simultaneously uncovers astonishing truths across countless other instances.

Bubbles and Their Colorful Secrets

When it comes to soap bubbles, have you ever pondered the origin of the rainbow-like colors displayed on their surface? Initially, I believed it was a result of refraction—similar to light passing through a prism and dispersing into a spectrum. To my surprise, it’s actually due to wave interference.

Wavelength & Frequency Explained

Picture the pen on an electrocardiogram (ECG). The paper moves at a steady pace, much like light. Although minor air variations exist, they can be overlooked.

If your heart rate doubles, the pen oscillates at double the speed. Consequently, the waves on the paper shorten, halving their wavelength. With light, there exists a broad range of wavelengths, with only a portion being visible to our eyes as colors. Red hues correspond to lower frequencies and longer wavelengths, while blue and violet shades represent higher frequencies with shorter wavelengths.

Demonstration of Wave Interference

During a vivid demonstration in school, we utilized a shallow, transparent water tank placed atop an overhead projector—an apparatus that projects images via a Fresnel lens. The tank featured a movable bar with two spherical balls, with an electric motor creating ripples by oscillating the bar up and down.

Interestingly, we witnessed two overlapping ripple patterns, along with lines of light and shadow radiating across the tank's surface, resembling spokes.

Understanding Interference

Interference occurs whenever waves overlap.

• Constructive Interference: When two peaks coincide, the water depth increases, resulting in diminished light transmission from below. Conversely, when two troughs align, the water depth decreases, enhancing light visibility.
• Destructive Interference: Though less visible in this experiment, there are points where a peak meets a trough, effectively canceling each other out.

The remaining areas experience a mix of these effects, which is precisely where the rainbow effect comes into play!

The Science Behind Rainbow Bubbles

A soap bubble's wall consists of water sandwiched between soap layers. This thickness varies across the bubble's surface due to air movements and evaporation. The semi-reflective properties of these soap layers allow most light to pass while reflecting some, especially at shallow angles.

Wavelengths of light are extremely short; for instance, blue light measures between 450-495 nanometers, while red light ranges from 620-750 nanometers. Bubble walls can be as thin as 10 nanometers and as thick as 1000 nanometers.

When light waves bounce from the inner soap layer, they interfere with those reflecting off the outer layer. Some waves sync constructively, while others destructively interfere, resulting in a colorful display of light.

The interplay of wavelengths, bubble thickness, and angles dictates how many complete waves fit between the soap layers. This variation leads to some colors appearing more vibrant, others dimmer, and some entirely canceled out.

The intricate relationship between bubble wall thickness and light wavelengths contributes to this phenomenon. It creates a chaotic blend of intensified, diminished, and absent colors, manifesting as a swirling rainbow.

Having previously regarded bubbles as mere visual delights, do you now perceive them differently? Has this understanding diminished or amplified their wonder?

That's my two cents on the matter.

Live well, stay safe, and create your own rainbows.

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