American Board of Ophthalmology (ABO) Practice Exam

The index of refraction of a material is defined as what?

1. The speed of light in water divided by the speed of light in air

2. The speed of light in air divided by the speed of light in the material

3. The amount of light absorbed by the material

4. The density of the material

The correct answer is: The speed of light in air divided by the speed of light in the material

The index of refraction of a material is defined as the ratio of the speed of light in a vacuum to the speed of light in that material. However, when discussing the index of refraction in a practical context, it is often expressed as the speed of light in air (which is considered approximately the same as in a vacuum) divided by the speed of light in the material. This definition allows for a clearer understanding of how light behaves as it passes through different substances. In this case, the selected option correctly identifies that the index of refraction is a measure of how much slower light travels in a specific medium compared to air. A higher index indicates that light slows down more in that material, affecting various optical phenomena, such as refraction, reflection, and the bending of light rays. The other options do not accurately define the index of refraction. The first option mentions the speed of light in water, which is not the standard reference point, as the index is generally referenced to air or vacuum. The third option incorrectly describes the index of refraction as the amount of light absorbed by the material, which is a different property related to the material's opacity or absorbance characteristics. Lastly, the fourth option refers to the density of the material