Exploring Quantum Physics through Hands-on Projects

CHAPTER 1

LIGHT AS A WAVE

Before we get into quantum physics, let’s understand the classical view of light. As early as 100 C.E., Ptolemy—a Roman citizen of Egypt—studied the properties of light, including reflection, refraction, and color. His work is considered the foundation of the field of optics. Ptolemy was intrigued by the way that light bends as it passes from air into water. Just drop a pencil into a glass of water and see for yourself!

As shown in Figure 1a, the pencil half under the water looks bent: light from the submerged part of the stick changes direction as it reaches the surface, creating the illusion of the bent stick. This effect is known as refraction, and the angle at which the light bends depends on a property of a material known as its refractive index.

Figure 1 Refraction of light: (a) A pencil dipped in water appears distorted because refraction causes light to bend when it passes from one substance into another, in this case from air to water. (b) A laser pointer clearly demonstrates Snell’s law of diffraction.

In the 1600s, Dutch mathematician Willebrord Snellius figured out that the degree of refraction depends on the ratio of the two materials’ different refractive indices. Most materials have a refractive index greater than 1, which means that as light enters the material from air, the angle of the ray in the material will become closer to perpendicular ...