ELECTROMAGNETIC WAVES AND THEELECTROMAGNETIC SPECTRUM

Chapter 12 Sections 1 & 2

Electric and Magnetic Fields

An electric charge is surrounded by an electric field

A moving electric charge produces a magnetic field

A moving magnetic field produces an electric field

Electromagnetic Waves

When an electric charge vibrates, its electric field changes, creating a changing magnetic field

The changing magnetic field produces a changing electric field and the process repeats

Electromagnetic Waves

The pattern of changing fields produces an electromagnetic 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 wave encounters an object, its fields exert forces on that object

Waves and Particles Electromagnetic waves can behave as

a particle, called a photon, whose energy depends on the frequency of the waves Photons are said to

have a dual nature – they can behave like waves and particles

The Electromagnetic Spectrum Electromagnetic waves are categorized by how they interact with matter. This depends on their frequency.

The entire range of EM frequencies is the Electromagnetic Spectrum.

Radio Waves

Radio waves are electromagnetic waves with the longest wavelengths (longer than 1mm)

They are used in communications, radar, microwaves, and MRIs

Microwaves

Microwaves are radio waves with wavelengths less than 30 cm but longer than 1mm

Cell phones and satellites use microwaves

• Microwaves in microwave ovens cause water molecules to rotate, heating your food

Infrared Waves

Infrared waves have wavelengths between 1mm and 750 billionths of a meter

Thermal energy travels in infrared waves

• Remote controls and CD-ROM drives also use infrared waves

Visible Light Visible light has wavelengths

ranging from 750 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 UV waves, have wavelengths of 400 billionths to 10 billionths of a meter

UV waves can cause skin damage such as sunburn, wrinkling, and cancer

Ultraviolet Light

UV light enables your body to make vitamin D

UV waves can kill bacteria by damaging its DNA

X-Rays

X-rays have wavelengths between ten billionths of a meter and ten trillionths of a meter

X rays are commonly used by doctors

and dentists

Gamma Rays

Gamma waves have wavelengths shorter than 10 trillionths of a meter

Gamma rays are produced by radioactive decay or other subatomic processes