Section 18.6

Electromagnetic Waves

and the

Electromagnetic Spectrum

Electromagnetic Waves

Electromagnetic Waves

• Electromagnetic waves are transverse waves produced by

the motion of electrically charged particles called photons.

• Electromagnetic waves do not require a medium and are

therefore able to travel at the speed of light.

• The speed of light = 3 x 108 m/s (300,000,000 m/s)

At this speed it can go around the world 8 times in one second.

Electromagnetic Waves

Electromagnetic Waves

Intensity

The intensity of light decreases as energy travel farther from the

source

The Waves of the Spectrum

• The different electromagnetic waves are arranged in the

electromagnetic spectrum.

• The electromagnetic spectrum is arranged in order of

increasing frequency and decreasing wavelength.

• The higher the frequency, the more energy per wave, and the

more potentially harmful the wave is.

Electromagnetic Spectrum

Low Energy High Energy

Electromagnetic Spectrum

Each kind of wave is characterized by a range of increasing

frequency from left to right.

Radio Waves (Low Energy)

Microwaves

Infrared Rays

Visible Light

Ultraviolent rays

X-Rays

Gamma Rays (High Energy)

Radio Waves

Radio waves are the lowest frequency and longest wavelength

in the spectrum.

They are used primarily for communications, such as cell

phones, T.V. and radio transmissions, and cordless devices

such as phones, speakers, etc.

Radio Waves

Include AM and FM radio stations

AM: Amplitude Modulation

The frequency waves stay the same and the amplitude of

the wave is varied

Radio Waves

Include AM and FM radio stations

FM: Frequency Modulation

The amplitude waves stay the same and the frequency of

the wave is varied.

• Microwaves are a type of radio wave.

• They are used in cell phones and microwave ovens.

• At normal levels, microwaves are harmless.

Microwaves

• Infrared radiation transfers energy in the form of heat.

• Examples include heat lamps and the warmth from the sun.

Special types of film and cameras can show infrared

radiation.

Infrared

• Visible light can be separated into 7 different colors

• From lowest frequency to highest, they follow the acronym:

ROY G. BIV

• When all 7 colors are combined together they produce

white light.

• When all 7 colors of the spectrum are absent, then the

“color” black is produced.

Visible Light

• Ultraviolent (U.V.) rays have applications in health and medicine,

and in agriculture.

• U.V. rays are potentially dangerous at high levels or with

prolonged exposure.

• U.V. rays can cause sunburns and skin cancer, and kill bacteria

and healthy cells.

Ultraviolent (U.V.) Rays

• X-Rays are used in medicine, industry, and transportation

to make pictures of the inside of solid objects.

• X-rays are potentially dangerous at moderate levels.

• X-rays can penetrate many materials such as skin, muscle,

and many fabrics

X-Rays

• Gamma radiation is high frequency waves which can be

extremely dangerous.

• Gamma rays are used in the medical field to kill cancer cells and

make pictures of the brain and in industrial situations as an

inspection tool.

• Destructive radiation from nuclear explosions

• Radio waves are the highest frequency and shortest wavelength

in the spectrum.

Gamma Rays

18.6 Assessment

Question #1

How are electromagnetic waves different from mechanical

waves?

Electromagnetic waves do not require a medium

Question #2

What is the speed of light?

3 x 108 m/s

Question #3

How do electromagnetic waves differ from one another?

Question #4

What happens to the intensity of light as energy moves away

from the light source?

The intensity of light decreases as energy travel father

from the source

Each kind of wave is characterized by a range of

increasing frequency

18.6 Assessment

Question #5

List each wave in the Electromagnetic spectrum from lowest

energy to highest energy.

Radio Waves (Low Energy)

Microwaves

Infrared Rays

Visible Light

Ultraviolent rays

X-Rays

Gamma Rays (High Energy)

18.6 Assessment