Day 34 MCAT Practice Question

Passage 6: Soap

Soap bubbles, despite their delicate and transient nature, have fascinated scientists

and laypeople alike for hundreds of years. When passing a white light source

through a soap bubble, a series of colorful bands can be observed along the surface

which changes with thickness of the soap film.

Scientists studying this phenomenon came up with an experiment to investigate

this behavior of light and physical properties of the soap bubbles themselves.

Materials:

• Soap solution

• White light source

• Camera with infrared, visible, and UV filters

• Spectrometer

• Polarizing filters

Procedure:

First, a soap solution was prepared with water, a small amount of soap, and glycerin.

The presence of glycerin was helpful to counter a primary limiting factor for the

stability of soap bubbles: surface tension. The bubbles were then illuminated with

the white light source, and the infrared, visible, and UV camera filters were used to

capture images of the three spectra.

Interference patterns were recorded as the bubbles expanded. Spectrometry was

utilized to analyze the light that was both reflected and transmitted through the film

at different angles. Results are tabulated below.

By the end of the experiment, the researchers concluded that the interference

patterns had the most observable effect on the vibrance of colors in the visible

spectrum. Infrared radiation was largely absorbed, but UV light experienced

significant scattering. When viewed through the polarizing filters, intensity of light

varied consistently with the orientation of the polarizer.

A beam of monochromatic light with a wavelength of 500 nm is shined into a

soap bubble with a thickness of 250nm and a refractive index of 1.33. Which

of the following represents an adjustment that can increase the energy of the

incident electromagnetic radiation?

A) Shine the light onto a bubble that has expanded less, increasing the

thickness of the film

B) Use a soap solution whose bubbles have a higher refractive index (>1.33)

C) Decrease the wavelength of the light to 400 nm

D) Increase the wavelength of the light to 600nm