Light

Light — page 1 — t s hard to imagine a world without light Most of us however take for granted just how complex and intriguing this form of energy is This volume investigates the nature of light from its basic behaviors such as reflection and refraction to its rela tionship to the concepts of space and time The properties of light have puzzled sci entists for centuries Isaac Newton believed that light was composed of particles Christiaan Huygens believed it traveled in the form of a wave Even up to the early 20th century scientists could not explain why light conformed to both particle and wave theory It was not until 1924 that Louis de Broglie put forth the idea that both theories were neces sary to explain the properties of light Light is one of several forms of energy that together are known as electromagnetic EM radiation various forms EM radiation The of are arranged on a spectrum according to their wavelengths which fall within a very wide range Light is the form of EM radiation that is visible to the human eye It occupies a very narrow band within the broad EM

Light — page 2 — INTRODUCTION from about 700 nanometers nm billionths of a meter down to about 400 nm The other forms of EM radiation which are invisible to the human eye include gamma rays X rays ultraviolet radiation infrared radiation and radio waves In other words the light we see when watching a sunset or reading a book is only a portion of the radiation that exists around us Without light vision would be impos sible We see the objects around us such as our friends faces or a dog running down the street only when light rays bounce off those objects surfaces and travel to our eyes The colors of those objects are a result of the wave lengths of the light waves that reach our eyes Light of different wavelengths appears as different colors For example red light has a long wavelength and violet light has a short wavelength Normally all the wavelengths or colors travel together as white light but white light separates into its individual colors when it strikes objects When white light strikes a ripe tomato for instance mostly red wave lengths reflect off the tomato while the other

Light — page 3 — LIGHT colors are absorbed This causes the tomato to look red Another aspect of light that has proved central to the study of physics is its speed Measuring the speed of light was a long standing challenge for scientists In 1905 Albert Einstein made a breakthrough As part of his theory of special relativity he put forth that the speed of light is the same for all observers Since then the speed of light has been considered a fundamental constant of nature In Einstein's famous relativity equa tion E mc the speed of light c serves as a constant linking the formerly separate con cepts of mass m and energy E The work of later scientists refined measurements of the speed of light which was eventually defined at exactly 299 792 458 meters 186 282 miles per second This volume explores the mysterious properties of light from its physical charac teristics to its intriguing behavior It provides a strong foundation for the study of this crucial and complex form of energy which fundamentally shapes our everyday lives and on the grandest scale provides a window on the structure of the universe 8

Light — page 4

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