http://www.ck12.org Chapter 19. Electromagnetism
19.4 The Electromagnetic Spectrum
Objective
The student will:
- Understand what the electromagnetic spectrum is.
Vocabulary
- electromagnetic spectrum:The entire range of eletromagnetic waves.
- gamma rays
- infrared waves
- microwaves
- radio waves
- ultraviolet light
- visible light
- x-rays
Introduction
The nature of light has, for most of human history, been a mystery. Galileo was one of the first scientists who
attempted to measure its velocity. He positioned two assistants with shuttered lanterns on high ground several
kilometers apart. At the first sight of light from one lantern, the other assistant was to open his lantern. Knowing the
distance between the two lanterns and measuring the time interval between the “light signals,” Galileo assumed he
could calculate the velocity of light. Galileo’s results were inconclusive- and no wonder! Indeed, the time interval
between the light signals was less than a hundred-thousandth of a second, and he had no clock! The best timing
tools of the age were the pendulum and water and sand “clocks.”