Objectives
By the end of this section, you will be able to:
- Explain the basic behavior of waves, including travelling waves and standing waves
- Describe the wave nature of light
- Use appropriate equations to calculate related light-wave properties such as frequency, wavelength, and energy
- Distinguish between line and continuous emission spectra
- Describe the particle nature of light
The nature of light has intrigued for scientists for centuries. In the seventeenth century, Isaac Newton performed experiments with lenses and prisms. These experiments showed that white light, in reality, was a combination of different colours. Newton explained his results using a “corpuscular” view of light. This view states that light is streams of extremely tiny particles travelling at high speeds, according to Newton’s laws of motion.
Meanwhile, Christiaan Huygens, had shown that optical phenomena, such as reflection and refraction, could explain light in terms of waves. These waves travel at high speed through a medium called “luminiferous aether”, which people believed permeated (filled) all space.
Early in the nineteenth century, Thomas Young conducted an experiment with light passing through narrow, closely spaced slits. The light produced interference patterns that Newtonian particles could not explain; Instead, these patterns were explained by waves. Later in the nineteenth century, the particle view of light became thoroughly discredited. James Clerk Maxwell developed his theory of electromagnetic radiation and showed that light was the visible part of a vast spectrum of electromagnetic waves.
All this furthered the evidence for the wave-like nature of light.
Classical Mechanics and Classical Electromagnetism
By the end of the nineteenth century, scientists viewed the physical universe as roughly comprising two separate domains:
- The first domain consists of matter composed of particles moving according to Newton’s laws of motion.
- The second domain states that electromagnetic radiation consisting of waves governed by Maxwell’s equations.
Today, these domains are referred to as classical mechanics and classical electrodynamics (or classical electromagnetism). There were a few physical phenomena that could not be explained within this framework yet scientists at that time were confident of the overall soundness of this framework. At the time, scientist would state that any aberrations were simply puzzling paradoxes and further studies would eventually resolve within the pre-existing framework. As we shall see, these paradoxes led to a contemporary framework that intimately connects particles and waves at a fundamental level called wave-particle duality, which has displaced the classical view.
Visible light and other forms of electromagnetic radiation play important roles in chemistry; used to infer the energies of electrons within atoms and molecules. Much of modern technology is based on electromagnetic radiation too. Some examples include: radio waves from a mobile phone, X-rays used by dentists, the energy used to cook food in your microwave, the radiant heat from red-hot objects, and the light from your television screen. All are forms of electromagnetic radiation that all exhibit wavelike behavior.