Chapter 18 The Electromagnetic Spectrum and Light Colorful neon lights brighten up a walkway in Chicago’s O’Hare Airport

18.1 Key Concepts How are electromagnetic waves different from mechanical waves? What is the maximum speed of light? How do electromagnetic waves differ from one another? What is the dual nature of electromagnetic radiation? What happens as light travels farther from its source?

You are surrounded by waves all the time, but may not realize it because most waves are _______________ invisible

What Are Electromagnetic Waves? Electromagnetic waves are produced when an electric ______________ vibrates or accelerates. charge Electromagnetic waves can travel through a _______________, or empty space, as well as through ____________. vacuum matter

What Are Electromagnetic Waves? Electromagnetic waves are _____________ waves consisting of changing ______________ fields and changing _______________ fields. transverse electric magnetic Electric Field Magnetic Field Direction of Wave

What Are Electromagnetic Waves? Like mechanical waves, electromagnetic waves carry _______________ from place to place. Electromagnetic waves differ from mechanical waves in how… they are ______________ they ________________ energy Electric Field produced travel Magnetic Field Direction of Wave

How They Are Produced Electromagnetic waves are produced by ______________ _______________ electric fields and magnetic fields. An electric field in a region of space exerts electric ______________ on charged _____________. A magnetic field in a region of space produces _______________ forces. Magnetic fields are produced by _______________, by changing electric fields, and by vibrating charges. constantly changing force particles magnetic magnets

What Are Electromagnetic Waves? How They Travel Changing electric fields produce changing ____________ fields, and changing magnetic fields produce changing ________________ fields, so the fields __________________ each other. The transfer of energy by electromagnetic waves traveling through matter or across space is called electromagnetic _____________________ magnetic electric regenerate radiation

The Speed of Electromagnetic Waves Which do you notice first… lightning or thunder? So in similar situations, ___________ travels faster than _________ The speed of light in a vacuum, _____, is… ____________________ Lightning light sound c 3.00 x 108 m/s

Octagonal Rotating Mirror Michelson’s Experiment In 1926, the American physicist Albert ____________ measured the speed of light more accurately than ever before. Michelson placed an eight-sided ______________ mirror and another mirror, that one ________________, about 35.4 kilometers apart. Michelson rotating stationary Mt. San Antonio Mirror 35.4 km Telescope Light Source Octagonal Rotating Mirror Mt. Wilson

Octagonal Rotating Mirror The Speed of Electromagnetic Waves Michelson _______________ a light beam as it traveled from one mountain to another and back again. timed Mt. San Antonio Mirror 35.4 km Telescope Light Source Octagonal Rotating Mirror Mt. Wilson

Electromagnetic waves vary in… ________________ All electromagnetic waves travel at the ____________ speed when in a vacuum, regardless of the observer’s motion. same Electromagnetic waves vary in… ________________ wavelength frequency

Wavelength and Frequency The speed of an electromagnetic wave is the _____________ of its wavelength and its frequency. The speed of electromagnetic waves in a vacuum is ________________, so the wavelength is ____________________ proportional to the frequency. product constant inversely

Wavelength and Frequency Calculating Wave Speed A radio station broadcasts a radio wave with a wavelength of 3.0 meters. What is the frequency of the wave? 3.00 x 108 m/s = 1.0 x 108 1/s 3.0 m = 1.0 x 108 Hz

Wave or Particle? Electromagnetic radiation behaves sometimes like a ___________ and sometimes like a stream of _______________ wave particles

Wave or Particle? The fact that light casts a _____________ has been used as evidence for ___________ the wave model of light and the particle model of light. shadow both

Wave or Particle? Interference pattern appears on screen. English physicist Thomas ___________ showed that light behaves as a ___________ Young Card with two slits wave Card with one slit Light source Light from single slit produces coherent light at second card.

Wave or Particle? Interference pattern appears on screen. When light passes through a single slit and then a double slit, it produces an _______________ pattern. Card with two slits interference Card with one slit Dark bands show __________ interference. Bright bands show __________ interference. Light source destructive constructive Light from single slit produces coherent light at second card.

Evidence for the _______________ Model Wave or Particle? Evidence for the _______________ Model When dim blue light hits the surface of a metal such as cesium, an _______________ is emitted. A brighter blue light causes even ____________ electrons to be emitted. Particle electrons more

Wave or Particle? The emission of electrons from a metal caused by light striking the metal is called the _______________________. In 1905, Albert ______________ (1879–1955) proposed that light, and all electromagnetic radiation, consists of ___________ of energy. These packets of electromagnetic energy are now called ____________________. Photoelectric effect Einstein packets photons

Each photon’s energy is proportional to the _______________ of the light. Red light photons have too _____________ ________________ to cause any electrons to be emitted from a metal surface. frequency little energy No electrons are emitted. Electrons are emitted. Bright red light or infrared rays Dim blue light or ultraviolet rays Metal plate Metal plate

Intensity The intensity of light decreases as photons travel ________________ from the source. farther

Intensity The closer you are to a source of light, the _______________ the light appears. Photons travel outward from a light source in ____________ directions. Near the light source, the photons spread through a ______________ area, so the light is ___________. Farther from the source, the photons spread over a _________________ area. brighter all smaller intense larger

How are electromagnetic waves different from all mechanical waves? Assessment Questions How are electromagnetic waves different from all mechanical waves? Electromagnetic waves don’t carry energy. Electromagnetic waves are invisible. Electromagnetic waves are longitudinal waves. Electromagnetic waves can travel through a vacuum.

2. The photoelectric effect is evidence that light behaves like Assessment Questions 2. The photoelectric effect is evidence that light behaves like a wave. a particle. both a wave and a particle. neither a wave nor a particle.

Assessment Questions 3. As photons travel farther from a light source, the intensity of light stays the same. True False