Electromagnetic WavesCHAPTER 15 SECTION 1 AND SECTION 2

Electromagnetic Waves• Waves cause something to vibrate

• Electromagnetic waves are produced when electric charges vibrate• The vibrating electric charge is surrounded by changing electric

and magnetic fields

• Unlike Mechanical waves, they travel through both space and matter

• Travel at 300,000 km/s in space

• Travel slower in matter

• Energy from a electromagnetic wave is radiant energy

Anatomy of an Electromagnetic Wave

• Is a combination of a electric field and a magnetic field

• They two field from waves at right angles to the direction the wave travels

• Transverse wave

Electromagnetic Waves as Particles• Electromagnetic waves can behave has both waves and

particles

• The particles are photons

• Photons are localized packets of energy that can behave like particles

• In this modern view, they define light as a collection of one or more photons propagating through space as electromagnetic waves

• Because electromagnetic waves behave as particles, the energy of a wave is measure using frequency.

The Electromagnetic Spectrum• Electromagnetic waves can have a wide range of

frequencies

• The entire range is known as the electromagnetic spectrum

Radio waves• A radio wave does not have rarefactions and

compressions so it cannot be heard

• Low frequency

• High (Long) Wavelength• Can be as short as a few mm to as long as several kilometers

• Shorter wavelength radio waves are microwaves

• Microwaves are used to heat food by exciting water molecules• The vibration of water molecules causes friction and generates

thermal energy

Other Uses of Radio Waves• RADAR• Stands for RAdio Detecting And Ranging

• Measure the time required for waves to bounce off an object and return

• Used by law enforcement to determine vehicle speed, track an aircraft, watercraft, or spacecraft.

• MRI• Allows doctors to produce

pictures of the inside of the body painlessly

Infrared (IR) Waves• Wavelength between 1

mm and 750 billionths of a meter

• Thermal energy is transmitted as infrared waves

• Used in• Remote controls

• Computers to read CDs and DVDs

• All objects emit IR Waves

Visible Light• Can be detected with the eye

• Wavelengths from 750 billionths to 400 billionths of a meter

Ultraviolet Waves• Range from 400 billionths to 10 billionths of 10 billionths

of a meter

• Can enter skin cells

• Can cause skin damage and cancer

• Most UV radiation that reaches Earth is longer wavelength

• Shorter wavelengths cause sun-burn

• Some exposure is necessary to help skin make Vitamin D

X-Ray and Gamma Rays• Shortest wavelengths

• Most energetic

• Doctors and dentists uses low does to get images of internal organs, bones, and teeth

• Really short X-rays are Gamma Rays

• Can penetrate lead by a several centimeters

• Can cause damage to living cells and tissues