# Electromagnetic Spectral Activities

## Objectives

Students will be able to:

1. explain how energy travels through space.
2. define and understand the different parts of a wave.
3. determine the make-up of visible light.
4. describe the various wavelengths in the electromagnetic spectrum.
5. examine the spectra of several different substances and then explain how this can be used to identify particular elements.

## Background Information

The electromagnetic spectrum is an array of electromagnetic radiation in order of wavelength. Electromagnetic radiation consists of electric and magnetic fields that travel through space and transfer energy from one place to another. Electromagnetic radiation sometimes has the properties of a wave and sometimes the properties of a particle. Usually electromagnetic radiation is considered to be a wave phenomenon.

A wave has several characteristics. The highest part of a wave is referred to as the crest. The lowest part of a wave is referred to as the trough. The horizontal distance between two successive crests or two successive troughs is called the wavelength. The number of crests or troughs passing a given point in a particular wave period is called the wave frequency. As the wave frequency increases, the wavelength decreases. The amount of energy carried depends on the wavelength. The shorter the wavelength, the more energy contained; the longer the wavelength, the less energy contained.

The electromagnetic spectrum is the range of wavelengths from short wavelengths (below visible light) to long wavelengths (above visible light). Electromagnetic radiation travels in straight lines at a fixed rate of the speed of light, 299,792.458 km/s, in a vacuum. No other observable body's rate can exceed the speed of light. The electromagnetic spectrum includes the following arranged in order from the shortest wavelength to the longest wavelength: gamma rays, x-rays, ultraviolet rays, visible light, infrared rays, microwaves, and radio waves. Light is the only visible part of the spectrum. Visible light makes up only a small part of the entire spectrum. It consists of a rainbow of colors ranging from red (longest wavelength) to violet (shortest wavelength). Gamma rays have wavelengths less than one ten-billionth of a meter. On the other extreme, radio waves have wavelengths from one millimeter to several kilometers.