18.1 electromagnetic waves chapter 18 the electromagnetic spectrum and light colorful neon lights...
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18.1 Electromagnetic Waves
Chapter 18The Electromagnetic Spectrum and Light
Colorful neon lights brighten up a walkway in Chicago’s O’Hare Airport
18.1 Electromagnetic Waves
How are electromagnetic waves different from mechanical waves?
18.1 Key Concepts
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?
18.1 Electromagnetic Waves
You are surrounded by waves all the time, but may not realize it because most waves are _______________invisible
18.1 Electromagnetic Waves
What Are Electromagnetic Waves?Electromagnetic waves are produced when an electric ______________ vibrates or accelerates.
Electromagnetic waves can travel through a _______________, or empty space, as well as through ____________.
charge
vacuum
matter
18.1 Electromagnetic Waves
Electromagnetic waves are _____________ waves consisting of changing ______________ fields and changing _______________ fields.
What Are Electromagnetic Waves?
ElectricField
MagneticField
Direction of Wave
transverseelectric
magnetic
18.1 Electromagnetic Waves
• Like mechanical waves, electromagnetic waves carry _______________ from place to place.
• Electromagnetic waves differ from mechanical waves in how…– they are ______________– they ________________
What Are Electromagnetic Waves?
ElectricField
MagneticField
Direction of Wave
energy
producedtravel
18.1 Electromagnetic Waves
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
magneticmagnets
18.1 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 _____________________
What Are Electromagnetic Waves?
magnetic
electricregenerate
radiation
18.1 Electromagnetic Waves
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
18.1 Electromagnetic Waves
Michelson’s ExperimentIn 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.
Octagonal Rotating Mirror
35.4 kmMirror
Light Source
Mt. Wilson
Mt. San Antonio
Telescope
Michelson
rotatingstationary
18.1 Electromagnetic Waves
Michelson _______________ a light beam as it traveled from one mountain to another and back again.
The Speed of Electromagnetic Waves
Mt. San Antonio
Mt. Wilson
Light Source
Telescope35.4 km
Mirror
Octagonal Rotating Mirror
timed
18.1 Electromagnetic Waves
All electromagnetic waves travel at the ____________ speed when in a vacuum, regardless of the observer’s motion.
Electromagnetic waves vary in…• ________________•________________
same
wavelength
frequency
18.1 Electromagnetic Waves
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.
Wavelength and Frequency
product
constantinversely
18.1 Electromagnetic Waves
Calculating Wave Speed
A radio station broadcasts a radio wave with a wavelength of 3.0 meters. What is the frequency of the wave?
Wavelength and Frequency
3.00 x 108 m/s
3.0 m= 1.0 x 108 1/s
= 1.0 x 108 Hz
18.1 Electromagnetic Waves
Wave or Particle?
Electromagnetic radiation behaves sometimes like a ___________ and sometimes like a stream of _______________
wave
particles
18.1 Electromagnetic Waves
The fact that light casts a _____________ has been used as evidence for ___________ the wave model of light and the particle model of light.
Wave or Particle?
shadow
both
18.1 Electromagnetic Waves
English physicist Thomas ___________ showed that light behaves as a ___________
Wave or Particle?
Light source
Card with one slit
Card with two slits
Interference pattern appears on screen.
Light from single slit produces coherent light at second card.
Young
wave
18.1 Electromagnetic Waves
When light passes through a single slit and then a double slit, it produces an _______________ pattern.
Wave or Particle?
Light source
Card with one slit
Card with two slits
Interference pattern appears on screen.
Light from single slit produces coherent light at second card.
Bright bands show __________ interference.
Dark bands show __________ interference.
interference
constructivedestructive
18.1 Electromagnetic Waves
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.
Wave or Particle?
Particle
electrons
more
18.1 Electromagnetic Waves
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 ____________________.
Wave or Particle?
Photoelectric effect
Einstein
packets
photons
18.1 Electromagnetic Waves
Bright red light or infrared
rays
Metal plate
Dim blue light or
ultraviolet rays
Metal plate
No electrons are emitted.
Electrons are emitted.
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
littleenergy
18.1 Electromagnetic Waves
Intensity
The intensity of light decreases as photons travel ________________ from the source. farther
18.1 Electromagnetic Waves
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.
Intensity
brighter
all
smaller intense
larger
18.1 Electromagnetic Waves
Assessment Questions
1. How are electromagnetic waves different from all mechanical waves? a. Electromagnetic waves don’t carry energy.
b. Electromagnetic waves are invisible.
c. Electromagnetic waves are longitudinal waves.
d. Electromagnetic waves can travel through a vacuum.
18.1 Electromagnetic Waves
Assessment Questions
2. The photoelectric effect is evidence that light behaves like a. a wave.
b. a particle.
c. both a wave and a particle.
d. neither a wave nor a particle.
18.1 Electromagnetic Waves
Assessment Questions
3. As photons travel farther from a light source, the intensity of light stays the same.
TrueFalse