# Bubbles turn black when they pop

• 947740

## Homework Statement

Why does a bubble turn black when it pops?

In terms of diffraction, interference, and Young's Experiment.

N/A

## The Attempt at a Solution

N/A

Check out thin film interference.

I would like to start by clarifying that bubbles do not always turn black when they pop. The color of a bubble when it pops can vary depending on various factors such as the type of soap used, the thickness of the bubble, and the lighting conditions. However, in general, bubbles may appear to turn black when they pop due to a phenomenon called thin-film interference.

Thin-film interference occurs when light waves reflect off the front and back surfaces of a thin film, such as the soap film of a bubble. When the thickness of the film is similar to the wavelength of visible light, interference patterns can be observed. This means that some colors of light will be amplified while others will be canceled out. When a bubble pops, the film becomes thinner and eventually disappears, causing the colors to shift and appear darker or even black.

This phenomenon can also be explained through Young's experiment, which demonstrates the wave nature of light. In this experiment, a thin film of soap solution is placed between two glass plates and illuminated with a monochromatic light source. As the film becomes thinner due to the pressure of the plates, the colors observed change due to interference of the light waves passing through the film.

In conclusion, the black color observed when a bubble pops is a result of thin-film interference and can be explained through the principles of diffraction, interference, and Young's experiment.

## 1. Why do bubbles turn black when they pop?

When a bubble pops, the thin film of soap that forms the bubble breaks and the water between the layers of soap evaporates quickly. This causes the bubble to collapse, trapping a small amount of air inside. The trapped air is then compressed, which increases the air's temperature and causes it to emit light in the infrared spectrum. This light is not visible to the human eye, but it can be detected by infrared cameras, making the bubble appear black.

## 2. Do all bubbles turn black when they pop?

No, not all bubbles turn black when they pop. The color of a bubble when it pops depends on the type of soap used, the thickness of the bubble film, and the amount of water present in the bubble. For example, bubbles made with thicker soap films or with less water may not turn black when popped.

## 3. Can the color of a bubble when it pops tell us anything about the bubble?

Yes, the color of a bubble when it pops can provide information about the bubble's composition. For example, if a bubble turns black when it pops, it means that the soap used to create the bubble contained a high concentration of water. Bubbles that do not turn black when popped may contain a lower concentration of water or a thicker soap film.

## 4. Is the black color of a popped bubble permanent?

No, the black color of a popped bubble is not permanent. As the trapped air inside the bubble cools down, the infrared light emission stops and the bubble will eventually turn back to its original color. This process can happen quickly, within a few seconds, or it may take several minutes depending on the environment and the size of the bubble.

## 5. Can we use bubbles turning black as a way to measure the amount of water in a soap solution?

Yes, bubbles turning black when they pop can be used as an indicator of the amount of water in a soap solution. The more water present in the solution, the higher the concentration of water in the bubble and the more likely it is to turn black when popped. This can be a useful tool for scientists and researchers studying the properties of soap and water solutions.