Chapter 18: Electromagnetic Waves Section 1: What are electromagnetic waves? Section 2: The Electromagnetic Spectrum

Electromagnetic 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 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 Light All electromagnetic waves travel at the speed of light in a vacuum (300,000 km/s OR 3.00 x 10 8 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 Particles 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 Spectrum 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 rays Mnemonic: Rims Make Impalas Very Ugly Xcept Gold

Radio 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.

Microwaves 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 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 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 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 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.