1.1 What is Chemistry?

http://www.ck12.org Chapter 5. Electrons in Atoms

5.1 Properties of Light

Lesson Objectives

• Describe the mathematical relationship between the speed, wavelength, and frequency of electromagnetic
  radiation.


• Describe the experiments that led to the discovery of the photoelectric effect and how the results were used to
  further inform our understanding of electrons and light.

Lesson Vocabulary

• light: A form of energy that behaves both as a particle and a wave.


• frequency: Inversely proportional to wavelength. Photons with high frequency light have more energy than
  photons with low frequency light (Zukav 1979).


• wavelength: The distance between two crests of a wave of light. The color of light is related to its wavelength.
  This is inversely proportional to frequency.


• photoelectric effect: Occurs when same types of electromagnetic radiation are shined on certain kinds of
  matter.


• photon: A description of light as particles.

Check Your Understanding

• What are the general properties of light?


• Are there substances whose color varies with changes in the environment or natural surroundings?

The Nature of Electromagnetic Radiation

Many kinds of waves exist, such as sound waves and water waves. Visiblelightis also a wave. It is a specific
type of a more general phenomenon called an electromagnetic wave. All waves can be described in terms of the
basic physical propertiesfrequencyandwavelength. These two properties are related to the speed of a wave by the
following equation:

speed =λν

whereλis the wavelength (usually expressed in meters) andνis the frequency (expressed in Hertz, where 1 Hz =
1 s−^1 ). All electromagnetic waves travel at a speed of 2.998× 108 meters/second (about 186,000 miles per hour),
which is known as the speed of light. We commonly abbreviate the speed of light as c when used in equations. In
the case of electromagnetic radiation, this equation becomes the following: