Electromagnetic Waves Waves of energy emitted from any accelerating charges Any object that is above absolute zero emits electromagnetic waves The entire range of possibilities is called the “Electromagnetic Spectrum” Still confused? Then click What are electromagnetic waves? To learn about the wavelength of photons click to the next slide. To move onto the EM spectrum click

Electromagnetic Waves Wavelength is : Where, c is the speed of light (3 x 108 m/s in a vacuum) λ is the wavelength in meters f is the frequency in Hertz

What is this “photon” term you’re throwing in there? A photon is a bundle (quantum) of light A photon has energy equal to Recall that h is Plank’s constant ν is the frequency of the radiation (wave)

What does a photon do? Both magnetic and electric forces involve the exchange of photons The photon has zero rest mass, but has momentum, can be deflected gravity, and can exert a force

TYPES OF ELECTROMAGNETIC WAVES GAMMA RAYS Emitted from the nuclei of atoms during radioactive decay or during high-speed collisions with particles. Ionizing Used in cancer treatment and for sterilization Sources: Cobalt 60, the inner core of the sun

X-RAYS Emitted when an electron moves from certain excited states back down to its ground state, or when an electron that is moving very quickly is suddenly stopped Two groups - long wavelength (soft x-rays) and shorter wavelength (hard x-rays) Used for radiography (x-ray photography) and to look at materials in industry for defects Sources:  emitted by heavy atoms after bombardment by an electron

ULTRAVIOLET Above the color violet Three groups - UV A, UV B, and UV C. “A” type: longest wavelength; least harmful UV B and UV C are absorbed by DNA in cells  Used by the body to produce vitamin D, to kill bacteria on objects, and for sun tanning Sources:   Ultra hot objects 5000°C or more

VISIBLE LIGHT White light: combination of all the colors Wavelength interval Frequency interval red ~ 625 to 740 nm ~ 480 to 405 THz orange ~ 590 to 625 nm ~ 510 to 480 THz yellow ~ 565 to 590 nm ~ 530 to 510 THz green ~ 520 to 565 nm ~ 580 to 530 THz cyan ~ 500 to 520 nm ~ 600 to 580 THz blue ~ 430 to 500 nm ~ 700 to 600 THz violet ~ 380 to 430 nm ~ 790 to 700 THz White light: combination of all the colors Rainbow: example of white light that has been separated into a continuous spectrum of colors The names of colors are assigned in order of their wavelengths Used for communications (fiber optics) Sources:   very hot objects

INFRARED Thought of as heat but is not always Far infrared energy is heat energy. All objects that have warmth radiate infrared waves Easily absorbed and re-radiated.  Used in remote controls,  surveillance, therapy of muscles Sources:  Humans, the sun

MICROWAVES 1 mm-1 dm in length Absorbed by water molecules – how microwave ovens heat food Used in telecommunications and power transmission Sources:  electric circuits, many stars, microwave ovens

RADIO WAVES 10 cm- 100,000+m in length Only cosmic waves the reach the surface of the Earth Cause of noise Divided into smaller frequency dependent groups called bands   Used for communications Sources:  transmitters and sparks from motors

Polarization Electric and magnetic fields which make up wave have preferred direction Can be horizontal, vertical, circular, or elliptical Most radio emission is unpolarized To learn more click here

Polarization y Electric Field Electric Field Electromagnetic Wave x y z E Horizontal Polarization Electric Field Magnetic Field Electromagnetic Wave Vertical Polarization x y Electric Field Electromagnetic Wave Magnetic Field

Why Do We Care About Radio Waves? Gadgets- cell phones, microwaves, remote controls, garage door openers Science- radio astronomy, atmospheric research