Chapter 12
Sections 1 & 2
Warm Up:
How is an electromagnetic wave created?
How is an electromagnetic wave different froma mechanical wave?
Warm Up:
How is an electromagnetic wave created?
An electromagnetic wave is made from vibratingelectric charges
How is an electromagnetic wave different froma mechanical wave?
An electromagnetic wave does not need matterto travel like a mechanical wave does
Electric and Magnetic FieldsReview
An electric charge issurrounded by an electricfield
A moving electric chargeproduces a magnetic field
A moving magnetic fieldproduces an electric field
Electromagnetic Waves
When an electriccharge vibrates, itselectric field changes,creating a changingmagnetic field
The changing magneticfield produces achanging electric fieldand the process repeats
Electromagnetic Waves
The pattern of changing fields produces anelectromagnetic wave
Electromagnetic waves
are transverse
waves with specific
wavelengths and
frequencies
Electromagnetic Waves
All Electromagnetic Waves travel at the“speed of light”
3 x 108 m/s
When an EM waveencounters anobject, its fieldsexert forces on thatobject
Waves and Particles
Electromagnetic waves can behave as aparticle, called a photon, whose energydepends on the frequency of the waves
Photons are said tohave a dual nature –they can behave likewaves and particles
The Electromagnetic Spectrum
Electromagnetic waves are categorized by how theyinteract with matter. This depends on their frequency.
The entire range of EM frequencies is theElectromagnetic Spectrum.
RadioWaves
Radio waves are electromagnetic waves withthe longest wavelengths (longer than 1mm)
They are used in communications, radar,microwaves, and MRIs
Microwaves
Microwaves areradio waves withwavelengths lessthan 30 cm butlonger than 1mm
Cell phones andsatellites usemicrowaves
• Microwaves inmicrowave ovenscause water moleculesto rotate, heating yourfood
Infrared Waves
Infrared waves havewavelengthsbetween 1mm and750 billionths of ameter
Thermal energytravels in infraredwaves
• Remote controls and
CD-ROM drives also use
infrared waves
Visible Light
Visible light has wavelengths ranging from750 billionths to 400 billionths of a meter
The spectrum of visible light ranges from red(longest ) to violet (shortest )
Visible Light
(ROYGBIV)
Ultraviolet Waves
Ultraviolet, or UVwaves, havewavelengths of 400billionths to 10billionths of a meter
UV waves can causeskin damage such assunburn, wrinkling,and cancer
Ultraviolet Light
UV light enables your body tomake vitamin D
UV waves can kill bacteria bydamaging its DNA
X-Rays
X-rays have wavelengthsbetween ten billionths of ameter and ten trillionths of ameter
X rays are commonly usedby doctors
and dentists
Gamma Rays
Gamma waves have wavelengths shorter than10 trillionths of a meter
Gamma rays are produced by radioactive decayor other subatomic processes
