Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 30 - Think and Do: 27


This is a writing exercise for the student, and answers will vary.

Work Step by Step

Sample: Hey grandma! Light is emitted by atoms when electrons fall from a higher energy level to a lower one. The energy is given up as a photon of light. In a lamp or in a flame, it is heat energy that initially excites the electrons to their so-called "excited state", after which they fall and emit light. In a laser, some external source of energy excites the electrons. Fluorescent dyes and paints are excited by ultraviolet light (which our eyes cannot see directly), but emit in the visible region of the spectrum, so they appear to glow vividly "in the dark". This is discussed on page 571 of my textbook. I hope you've replaced the old-style incandescent light bulbs (the ones with the heated filament) in your house with compact fluorescents or LED bulbs. CFLs and LEDs are over 4 times more efficient than the classic bulbs - you get more visible light for your buck, and less of the energy is wasted as (invisible) heat!
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