LIGHT • Light is a kind of energy that travels in waves. • Light can pass through some things, but not others. • Light travels very fast and in straight lines.
Lightning • Light travels faster than sound. • That is why the lightning is seen before the thunder is heard.
WAVE a disturbance that transfers energy • Carries energy from one place to another • Classified by what they move through • Mechanical Wavesthe energy is transferred by vibrations of medium (medium = substance or material which carries the wave)ex/ ocean waves move through water • Electromagnetic waves (EM Waves)the energy moves through disturbances in the electromagnetic field.
Making a pulse MECHANICAL WAVES require amedium(the material through which the disturbance is moving) to transmit energy travel through & gradually lose energy to that medium • Examples: • water, sound, rope, & spring waves • Mechanical Media: • water, air, rope, spring
ELECTROMAGNETIC WAVES Don’t require amedium(the material through which the disturbance is moving) to transmit energy The wave, or "disturbance," is in an invisible thing called the electric force field. Examples: • Radio waves, microwaves, light, x rays, gamma rays They can travel through empty space. For more information and interactives go to http://www.colorado.edu/physics/2000/waves_particles/
Electromagnetic Waves • They travel as vibrations in electrical and magnetic fields. • Have some magnetic and some electrical properties to them. • Called transverse waves, wave motion is perpendicular to the direction the energy moves • http://einstein.byu.edu/~masong/htmstuff/WaveTrans.html • http://hermes.ffn.ub.es/~albert/ones/wavemotion.html
Electromagnetic Waves • Light is an electromagnetic wave • A transverse wave that does not require a medium, therefore it can travel through space • Light can travel through certain media • Light is part of a range of electromagnetic waves known as the electromagnetic spectrum
TRANSVERSE WAVE STRUCTURE AMPLITUDEresting to max peak CREST (peak) WAVELENGTH TROUGH
CHARACTERISTICS OF TRANSVERSE WAVES Waves are described according to their • Amplitudemeasures DISPLACEMENTsize of the disturbance • Wavelength distance of a “repeating unit”Also called a cycle • Velocity vspeed = how fast wave travels
AMPLITUDE • Distance between “rest & crest” or “rest & trough” • Gives indication of “power” or “strength” of wave(magnitude of earthquake = Richter scale) • Does not affect velocity of wave • Determines loudness (sound) or brightness (EM wave)
WAVELENGTH • Distance between any two repeating points on a wavecrest-crest, trough-trough,expansion-expansion, compression-compression • Determines what colorswe see; what notes we hear (pitch) • Shorter wavelengths have more cycles per minute because they aren’t as long
VELOCITY v • Rate at which the energy travels; speed & direction • Depends on medium • Mechanical waves travel faster through dense mediums • EM Waves are faster through less dense mediums
FREQUENCY ƒ • How oftennumber of wavelengths that pass any point per second • measured in wavelengths/second or cycles/secondHertz (Hz) = number of wavelengths in 1 second • Frequency is related to velocity: v = ƒ
Speed of Electromagnetic waves Electromagnetic waves travel VERY FAST – around 300,000 kilometres per second (the speed of light in avacuum ). At this speed they can go around the world 8 times in one second.
Wavelength and frequency • Speed of light in any medium is a constant • Speed = wavelength x frequency • Large wavelength = low frequency • Small wavelength = high frequency
Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency
Notice the wavelength is long (Radio waves) and gets shorter (Gamma Rays)
RADIO WAVES Have the longest wavelengths and lowestfrequencies of all the electromagnetic waves.
Global Positioning Systems (GPS) measure the time it takes a radio wave to travel from several satellites to the receiver, determining the distance to each satellite.
A radio picks up radio waves through an antenna and converts it to sound waves. • Each radio station in an area broadcasts at a different frequency. • # on radio dial tells frequency.
MRI • (MAGNETIC RESONACE IMAGING) • Uses Short wave radio waves with a magnet to create an image.
MICROWAVES Have the shortest wavelengths and the highest frequency of the radio waves.
Used in microwave ovens. • Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.
RADAR (Radio Detection and Ranging) • Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.
INFRARED RAYS Infrared= below red Shorter wavelength and higher frequency than microwaves.
You can feel the longest ones as warmth on your skinWarm objects give off more heat energy than cool objects.
VISIBLE LIGHT Shorter wavelength and higher frequency than infrared rays. Electromagnetic waves we can see. Longest wavelength= red light Shortest wavelength= violet (purple) light
When light enters a new medium it bends (refracts). Each wavelength bends a different amount, allowing white light to separate into it’s various colors ROYGBIV.
ULTRAVIOLET RAYS Shorter wavelength and higher frequency than visible light Carry more energy than visible light
Used to kill bacteria. (Sterilization of equipment)
Too much can cause skin cancer. Use sun block to protect against (UV rays)
X- RAYS Shorter wavelength and higher frequency than UV-rays Carry a great amount of energy Can penetrate most matter.
Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)
Too much exposure can cause cancer • (lead vest at dentist protects organs from unnecessary exposure)
Used by engineers to check for tiny cracks in structures. • The rays pass through the cracks and the cracks appear dark on film.
GAMMA RAYS Shorter wavelength and higher frequency than X-rays Carry the greatest amount of energy and penetrate the most.
Used in radiation treatment to kill cancer cells. Can be very harmful if not used correctly.
Brief Summary A.All electromagnetic waves travel at the same speed. (300,000,000 meters/second) in a vacuum. B. They all have different wavelengths and different frequencies. • Long wavelength-lowest frequency • Short wavelength highest frequency • The higher the frequency the higher the energy.
Visible spectrum Wavelength of visible light ranges from 700nm to 400nm. nm = nanometer (10-9 m) or 0.0000007m to 0.0000004m
Transparent • An object that lets all light pass through it is called transparent. • These objects are transparent: clear glass, eyeglasses, window, fish tank, clear plastics, and transparent tape.
Translucent • An object that lets some light pass through it is called translucent. • These objects are translucent: waxed paper, sunglasses, frosted glass, and thin fabrics.
Opaque • An object that lets no light pass through it is called opaque. • These objects are opaque: rock, metal, wood, fog, aluminum foil, thick paper, and brick.
Refraction • Light interacts with transparent media and refracts or bends • Refraction of light occurs whenever light travels from one transparent medium into another • Light waves travel at different speeds through different media
Refraction • Light waves travel at different speeds through different media when the light changes speeds, it bends
Index of Refraction • The “light slowing factor” is called the index of refraction (n) • glass has n = 1.52, meaning that light travels about 1.5 times slower in glass than in vacuum • water has n = 1.33 • air has n = 1.00028 • vacuum is n = 1.00000 (speed of light at full capacity)