15.1 The Electromagnetic Spectrum

• Light is a form of electromagnetic radiation (EMR)
• The term light usually refers to visible light, but this is not the only form of EMR
• Electromagnetic radiation is generated by a moving electric charge, that is, by an electric current
• As you will see when you study electricity, an electric current generates both an electric field, E, and a magnetic field, B
• • Wavelength—The distance between two wave crests or two wave troughs, expressed in various metric measures of distance
  • Frequency—The number of wave crests that pass a point per second, expressed in hertz (Hz or s–1)
  • Amplitude: The height of the crest above the null point
• The electromagnetic spectrum is made up of a broad range of frequencies of electromagnetic radiation.
• All frequencies of EM radiation travel at the same speed in a vacuum and consist of an electric field and a magnetic field. The types of EM radiation have different frequencies and wavelengths, and different energies and penetrating ability.