Chapter 18: Chapter 18: Electromagnetic Electromagnetic

WavesWavesSection 1: What are Section 1: What are

electromagnetic waves?electromagnetic waves?Section 2: The Section 2: The

ElectromagneticElectromagneticSpectrumSpectrum

Electromagnetic WavesElectromagnetic Waves• Electromagnetic waves are made by

vibrating electric charges and can travel without matter being present.

• Vibrating electric charges produce magnetic fields and the resulting magnetic fields then produce electric charges.

• Electromagnetic waves travel outward from the source in all directions.

Moving ParticlesMoving Particles• As electromagnetic waves encounter

particles (atoms) the vibrations that they carry are transferred to these particles.

• Electromagnetic waves carried by the Sun cause the particles that make up your skin to vibrate and as a result transfer radiant energy as warmth.

Speed of LightSpeed of Light• All electromagnetic waves travel at the

speed of light in a vacuum (300,000 km/s OR 3.00 x 108 m/s.

• As light travels through air or more dense materials, the speed of the wave decreases somewhat (slows down as density increases).

• In air, the speed of light is slightly less than 300,000 km/s.

Waves as Particles and Waves as Particles and Particles as WavesParticles as Waves

• Through the work of Heinrich Hertz and later work by Albert Einstein, it was discovered that light could behave as a particle called a photon.

• It has also been discovered that particles can behave as waves. If electrons are propelled through small openings, diffraction takes place and the electrons take on patterns associated with wave motion.

The Electromagnetic The Electromagnetic SpectrumSpectrum

• The electromagnetic spectrum goes from waves with a low frequency (larger wavelength) to a very high frequency (very small wavelength).

• Below is the order of the Electromagnetic Spectrum (lowest freq. to highest freq.).

Radio Waves Microwaves Infrared Waves Visible Light Ultraviolet Waves X rays

Gamma raysMnemonic: Rims Make Impalas Very Ugly Xcept

Gold

Radio WavesRadio Waves• Radio waves have the lowest

frequency, but the highest wavelength on the electromagnetic spectrum.

• Radio waves are not audible to us as sounds, it takes special receiver tuned in at a specific frequency to pick up radio waves.

MicrowavesMicrowaves• Microwaves have a wavelength that is slightly

shorter than radio waves. • Microwaves are commonly used for cell

phones, satellite communication and microwave ovens.

• Microwave ovens cook food by rapidly heating water molecules. Microwaves DO NOT cook from the inside out as some people commonly state. The insides of food is cooked by conduction of heat from the outer regions of the food.

• RADAR and MRI (Magnetic Resonance Imaging) are types of microwave transmissions.

Infrared WavesInfrared Waves• Infrared waves are just above the

frequency of the visible spectrum of light.

• Remote controls and CD players are common devices that use infrared waves to operate.

• Infrared imagery (thermogram) is used to detect different temperature regions in objects. Think of the way the alien saw the world in the movie “Predator.”

Visible LightVisible Light• Visible Light is the range of

electromagnetic waves that you can detect with your eyes.

• The visible spectrum begins with the color red and progresses to violet.

• Below is the order from longest wavelength to shortest.Red Orange Yellow Green Blue Indigo Violet

Mnemonic: ROY G. BIV

Ultraviolet WavesUltraviolet Waves• Ultraviolet waves are just below the

wavelength of visible light.• Ultraviolet waves are energetic enough to

enter skin cells.• Overexposure to UV rays can lead to skin

cancer and accelerate the aging of the skin by producing wrinkles.

X Rays and Gamma RaysX Rays and Gamma Rays• X rays are very valuable as an

imaging tool to diagnose problems in the dense regions of the body like bones and teeth.

• Gamma rays can be used medically to kill off cancer cells. Gamma rays have the shortest wavelength but the highest frequency and energy.