Chapter 18 – The Chapter 18 – The Electromagnetic Electromagnetic

Spectrum and Spectrum and LightLight

Jennie L. BordersJennie L. Borders

Section 18.1 – Section 18.1 – Electromagnetic WavesElectromagnetic Waves

Electromagnetic WavesElectromagnetic Waves are are transversetransverse waves consisting of waves consisting of changing changing electric fieldselectric fields and and changing changing magnetic fieldsmagnetic fields..

An An electric fieldelectric field in a region of space in a region of space exerts electric forces on exerts electric forces on charged charged particlesparticles..

A A magnetic fieldmagnetic field in a region of space in a region of space produces magnetic forces.produces magnetic forces.

Electromagnetic WavesElectromagnetic Waves

Electromagnetic waves are Electromagnetic waves are produced when an produced when an electric charge electric charge vibrates or acceleratesvibrates or accelerates..

This is a This is a transversetransverse wave because wave because the particles are vibrating the particles are vibrating perpendicularperpendicular to the direction of the to the direction of the wavewave..

Electromagnetic WavesElectromagnetic Waves

Electromagnetic wavesElectromagnetic waves can travel can travel through a through a vacuum, or empty spacevacuum, or empty space, , as well as through matter.as well as through matter.

The The transfer of energytransfer of energy by by electromagnetic waves traveling electromagnetic waves traveling through matter or across space is through matter or across space is called called electromagnetic radiationelectromagnetic radiation..

Speed of Speed of Electromagnetic WavesElectromagnetic Waves

The The speed of lightspeed of light in a vacuum is in a vacuum is 3.0 3.0 x 10x 1088 m/s m/s..

In a In a vacuumvacuum, all electromagnetic , all electromagnetic waves travel at the same waves travel at the same speedspeed..

Electromagnetic waves vary in Electromagnetic waves vary in wavelength and frequencywavelength and frequency..

Electromagnetic Wave Electromagnetic Wave SpeedSpeed

Formula for speed of a wave – Formula for speed of a wave – v = v = x x

For electromagnetic waves, v is always For electromagnetic waves, v is always the speed of light which is represented the speed of light which is represented by a c.by a c.

c = c = x x c = speed of light (3.0 x 10c = speed of light (3.0 x 1088 m/s) m/s) = wavelength (m)= wavelength (m) = frequency (Hz)= frequency (Hz)

Sample ProblemSample Problem

A radio station broadcasts a radio A radio station broadcasts a radio wave with a wavelength of 3.0m. What wave with a wavelength of 3.0m. What is the frequency of the wave?is the frequency of the wave?

c = c = x x = c/ = c/c = 3.0 x 10c = 3.0 x 1088 m/s m/s = 3.0 x 10 = 3.0 x 1088 m/s / m/s / 3.0m3.0m

= 3.0m= 3.0m = 1.0 x = 1.0 x 101088 Hz Hz

= ?= ?

Practice ProblemsPractice Problems

The radio waves of a particular AM The radio waves of a particular AM radio station vibrate 680,000 times radio station vibrate 680,000 times per second. What is the wavelength per second. What is the wavelength of the wave?of the wave?

A global positioning satellite A global positioning satellite transmits a radio wave with a transmits a radio wave with a wavelength of 19cm. What is the wavelength of 19cm. What is the frequency of the radio wave?frequency of the radio wave?

c = x = c/ = 3.0 x 108 m/s / 680,000 1/s = 440m

19cm = 0.19mc = x = c/ = 3.0 x 108 m/s / 0.19m = 1.6 x 109 Hz

Wave or Particle?Wave or Particle?

Electromagnetic radiationElectromagnetic radiation behaves behaves sometimes like a sometimes like a wavewave and and sometimes like a sometimes like a particleparticle..

Evidence for a Evidence for a wavewave includes the includes the fact that light can produce fact that light can produce constructive and destructive constructive and destructive interferenceinterference..

Wave or Particle?Wave or Particle?

Evidence for a Evidence for a particleparticle includes the includes the fact that light causes the fact that light causes the photoelectric effectphotoelectric effect..

The emission of The emission of electronselectrons from a from a metalmetal caused by light striking the caused by light striking the metal is called the metal is called the photoelectric photoelectric effecteffect..

PhotonsPhotons

In 1905, In 1905, Albert EinsteinAlbert Einstein proposed proposed that light, and all electromagnetic that light, and all electromagnetic radiation, consists of radiation, consists of packets of packets of energy called photonsenergy called photons..

Each Each photon’s energyphoton’s energy is proportional is proportional to the to the frequencyfrequency of the light. of the light.

IntensityIntensity

PhotonsPhotons travel outward from a light travel outward from a light source in all source in all directionsdirections..

The The intensityintensity of light of light decreasesdecreases as as photons travel photons travel fartherfarther from the from the source.source.

Section 18.1 AssessmentSection 18.1 Assessment

How fast does light travel in a vacuum?How fast does light travel in a vacuum? What makes electromagnetic waves What makes electromagnetic waves

different from one another?different from one another? What happens to the intensity of light What happens to the intensity of light

as photons move away from the light as photons move away from the light source?source?

What is the wavelength of an AM radio What is the wavelength of an AM radio wave in a vacuum if its frequency is wave in a vacuum if its frequency is 810 kHz?810 kHz?810 kHz = 810,000Hz

c = x = c/ = 3.0 x 108 m/s / 810,000 1/s = 370m

Section 18.2 – The Section 18.2 – The Electromagnetic SpectrumElectromagnetic Spectrum

A scientist observed that when light A scientist observed that when light is passed through a is passed through a prismprism the the temperature of the light is temperature of the light is lowerlower at at the blue end and the blue end and higherhigher toward the toward the red end.red end.

He also concluded that there was He also concluded that there was invisible radiationinvisible radiation beyond the visible beyond the visible spectrum.spectrum.

Electromagnetic Electromagnetic SpectrumSpectrum

The full range of frequencies of The full range of frequencies of electromagnetic radiation is called electromagnetic radiation is called the the electromagnetic spectrumelectromagnetic spectrum..

The electromagnetic spectrum The electromagnetic spectrum includes includes radio waves, infrared rays, radio waves, infrared rays, visible light, ultraviolet rays, X-rays, visible light, ultraviolet rays, X-rays, and gamma raysand gamma rays..

Radio WavesRadio Waves Radio wavesRadio waves are used in radio and are used in radio and

television technologies, as well as in television technologies, as well as in microwave ovens and radarmicrowave ovens and radar..

In In AMAM radio, the stations have radio, the stations have signals with varying signals with varying amplitudesamplitudes..

In In FMFM radio, the stations have radio, the stations have signals with varying signals with varying frequenciesfrequencies..

Radio WavesRadio Waves

The The shortestshortest radio waves are called radio waves are called microwavesmicrowaves..

Microwaves also carry Microwaves also carry cell phonecell phone conversations.conversations.

Infrared RaysInfrared Rays

Infrared raysInfrared rays are used as a source of are used as a source of heatheat and to discover areas of heat and to discover areas of heat differences.differences.

ThermogramsThermograms are color-coded are color-coded pictures that show variations in pictures that show variations in temperaturetemperature..

Visible LightVisible Light

Ultraviolet RaysUltraviolet Rays

Ultraviolet radiationUltraviolet radiation has higher has higher frequencies than frequencies than violetviolet light. light.

Ultraviolet rays have Ultraviolet rays have applicationsapplications in in health and medicine, and in health and medicine, and in agriculture.agriculture.

X-RaysX-Rays

X-raysX-rays have high energy and can have high energy and can penetrate matter that penetrate matter that lightlight cannot. cannot.

X-rays are used in X-rays are used in medicinemedicine, , industry, and transportation to make industry, and transportation to make picturespictures of the inside of solid of the inside of solid objects.objects.

Gamma RaysGamma Rays

Gamma raysGamma rays have the have the shortestshortest wavelengths in the electromagnetic wavelengths in the electromagnetic spectrum, about 0.005nm or less.spectrum, about 0.005nm or less.

Gamma rays are used in the medical Gamma rays are used in the medical field to kill field to kill cancer cellscancer cells and make and make pictures of the pictures of the brainbrain, and in , and in industrial situations as an inspection industrial situations as an inspection tool.tool.

Section 18.2 AssessmentSection 18.2 Assessment

List the kinds of waves included in List the kinds of waves included in the electromagnetic spectrum, from the electromagnetic spectrum, from longest to shortest wavelength.longest to shortest wavelength.

How are AM radio waves different How are AM radio waves different from FM radio waves?from FM radio waves?

What type of electromagnetic waves What type of electromagnetic waves are microwaves?are microwaves?

Section 18.3 – Behavior Section 18.3 – Behavior of Lightof Light

Materials can be Materials can be transparent, transparent, translucent, or opaquetranslucent, or opaque..

A A transparenttransparent material transmits material transmits light, which means it allows most of light, which means it allows most of the light that strikes to the light that strikes to pass through pass through itit..

A A translucenttranslucent material material scattersscatters light. light. An An opaqueopaque material either material either absorbs or absorbs or

reflectsreflects all of the light that strikes it. all of the light that strikes it.

Interactions of LightInteractions of Light

When light strikes a new medium, When light strikes a new medium, the light can be the light can be reflected, absorbed, reflected, absorbed, or transmittedor transmitted..

When light is transmitted, it can be When light is transmitted, it can be refracted, polarized, or scatteredrefracted, polarized, or scattered..

ReflectionReflection An An imageimage is a copy of an object formed is a copy of an object formed

by by reflected (or refracted)reflected (or refracted) waves of waves of light.light.

Regular reflectionRegular reflection occurs when occurs when parallel light waves strike a surface parallel light waves strike a surface and reflect all in the and reflect all in the same directionsame direction..

Diffuse reflectionDiffuse reflection occurs when parallel occurs when parallel light waves strike a rough surface, and light waves strike a rough surface, and reflect in reflect in many different directionsmany different directions..

RefractionRefraction

A A miragemirage is a false or is a false or distorteddistorted image.image.

PolarizationPolarization

Light with waves that vibrate in only Light with waves that vibrate in only one planeone plane is is polarized lightpolarized light..

ScatteringScattering

ScatteringScattering means that light is means that light is redirectedredirected as it passes through a as it passes through a mediummedium..

Section 18.3 AssessmentSection 18.3 Assessment

Explain the differences among Explain the differences among opaque, transparent, and opaque, transparent, and translucent materials. translucent materials.

List and explain three things that List and explain three things that can happen to a light wave when it can happen to a light wave when it enters a new medium.enters a new medium.

What is the difference between What is the difference between diffuse reflection and regular diffuse reflection and regular reflection?reflection?