18.1 electromagnetic waves chapter 18 the electromagnetic spectrum and light colorful neon lights...

18.1 Electromagnetic Waves

Chapter 18The Electromagnetic Spectrum and Light

Colorful neon lights brighten up a walkway in Chicago’s O’Hare Airport


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?


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.

Electromagnetic waves can travel through a _______________, or empty space, as well as through ____________.

charge

vacuum

matter


Electromagnetic waves are _____________ waves consisting of changing ______________ fields and changing _______________ fields.

What Are Electromagnetic Waves?

ElectricField

MagneticField

Direction of Wave

transverseelectric

magnetic


• Like mechanical waves, electromagnetic waves carry _______________ from place to place.

• Electromagnetic waves differ from mechanical waves in how…– they are ______________– they ________________


ElectricField

MagneticField

Direction of Wave

energy

producedtravel


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


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

electricregenerate

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


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


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


All electromagnetic waves travel at the ____________ speed when in a vacuum, regardless of the observer’s motion.

Electromagnetic waves vary in…• ________________•________________

same

wavelength

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.

Wavelength and Frequency

product

constantinversely


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


Wave or Particle?

Electromagnetic radiation behaves sometimes like a ___________ and sometimes like a stream of _______________

wave

particles


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


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


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


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


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


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


Intensity

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


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


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.



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.



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

TrueFalse

18.1 electromagnetic waves chapter 18 the electromagnetic spectrum and light colorful neon lights...

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