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The index of refraction (n) is a measure of how much light slows down when it enters a medium from a vacuum. It’s a fundamental property of materials, describing how light bends or refracts. For example, the index of refraction of air is close to 1, meaning light travels almost as fast in air as it does in a vacuum.
When light enters a medium like water or glass, it slows down, and its wavelength changes, causing the light to bend. The index of refraction is crucial in various optical devices, including lenses, microscopes, and interferometers.
The Michelson interferometer uses the principle of index of refraction to measure the shifts in light waves. By understanding how light behaves in different mediums, scientists can calculate precise measurements in experiments.

Fringe shift is an important concept in interferometry. It refers to the movement of dark or bright fringes observed when two beams of light combine and interfere. In the context of the Michelson interferometer, fringe shifts occur when there are changes in the distance that light travels.
The calculation of fringe shift in the example can be represented by the formula: \[ \Delta N = \frac{2L \Delta n}{\lambda} \], where \( \Delta N \) is the fringe shift, \( L \) is the length of the chamber, \( \Delta n \) is the change in the index of refraction, and \( \lambda \) is the wavelength of the light used.
By rearranging the formula to solve for \( \Delta n \), we use: \[\Delta n = \frac{\Delta N \cdot \lambda}{2L}\].
In the problem, substituting the given values, we find the change in the index of refraction when air is evacuated from the chamber. This shift tells us how much the refractive index has changed, enabling us to determine the index of refraction of air.

The wavelength of light is the distance between successive crests of a light wave. It is usually measured in nanometers (nm). In the provided exercise, the wavelength used is \(500\ nm\). The wavelength is a key factor in calculating the fringe shifts in a Michelson interferometer.
Light's wavelength determines its color and how it interacts with different materials. In experiments like these, it's essential to use a known and consistent wavelength to ensure accurate results.
The wavelength affects the interference pattern that forms inside an interferometer. Shorter wavelengths lead to more closely spaced fringes, while longer wavelengths produce more widely spaced fringes. Therefore, accurately knowing the wavelength is critical for precise measurements in optical experiments.