11.9 Light and photons

Light illuminates the things around us. It can be as dim and small as a faraway star on a clear night or as harsh and bright as the sun or the output of welding equipment. Understanding the nature of light was a central research direction in physics in the nineteenth and early twentieth centuries. light

The answers were far more complicated than anyone imagined, gave birth to quantum mechanics, and involved the electromagnetic spectrum well beyond visible light.

11.9.1 Photons

Does light behave like a wave, with amplitude A (height) and wavelength λ, as in Figure 11.24? λ is the distance between two wave crests or other corresponding points. light$wavelength λ`italic

Figure 11.24: Metrics associated with waves

Or does light behave like a particle with a well-defined shape, shooting off in various directions, as in Figure 11.25? Can particles have...