Light travels in straight lines.
Dec 17, 2015
WAVE
• Carries energy from one place to another • Classified by what they move through
1. Mechanical Wavesthe energy is transferred by vibrations of medium (medium = substance or material which carries the wave)ex/ ocean waves move through water
2. Electromagnetic waves (EM Waves)the energy moves through disturbances in the electromagnetic field.
a disturbance that transfers energy
MECHANICAL WAVES
travel through & gradually lose energy to that medium
• Examples:– water, sound, rope, &
spring waves
• Mechanical Media:– water, air, rope, spring
require a medium (the material through which the
disturbance is moving) to transmit energy
Making a pulse
ELECTROMAGNETIC WAVES
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.
Don’t require a medium (the material through which the disturbance is moving) to transmit energy
For more information and interactives go tohttp://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
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 v speed = 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 wave
crest-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
• measured in wavelengths/second or cycles/second
Hertz (Hz) = number of wavelengths in 1 second
• Frequency is related to velocity: v = ƒ
How often number of wavelengths that pass any point per second
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.
Speed of Electromagnetic waves
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
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.
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.
MICROWAVES
INFRARED RAYS
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
lightShortest 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
X- RAYS
Shorter wavelength and higher frequency than UV-raysCarry a great amount of energyCan 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)
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.
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)
Index of Refraction
• The larger the index of refraction, the slower the speed of light in the medium
• The larger the index of refraction, the more the light bends (the bigger the difference between the angle of incidence and the angle of refraction)
Refraction at a plane surface
• Light bends at interface between two media
• Measurethe anglesfrom the normal line(N)
• I=Incidence• R=Refraction
Refraction at a plane surface
• Light bends and makesthe straw look brokenor the root beer glass look thinner than it is(when the glass is inwater, you can see howthick it really is)
Convex Lenses
Thicker in the center than edges. – Lens that converges
(brings together) light rays.
– Magnifies a flat image
Concave Lenses
• Lenses that are thicker at the edges and thinner in the center. – Diverges light rays – Reduces an image
Refraction of light through flat plastic
What the lines really look like.
What the lines look like when viewed through an acrylic semicircle placed between points A and B
Refraction of light through concave or convex lenses
What the lines really look like.
What the lines look like when viewed through an convex or concave lenses placed between points A and B
Reflections• Reflect is when light
or an image bounces back off an object’s surface.
• Light can bounce back off an opaque object.
Law of Reflection
• Light travels in straight lines• Reflection off a flat surface follows a
simple rule:– angle in (incidence) equals angle out
(reflection)– angles measured from surface “normal”
(perpendicular)
Color
Make a Splash with Color http://www.thetech.org/exhibits/online/color/overview/
What wavelength goes with which color?
http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
Color of transparent materials
• Light passes through transparent materials
• Some transparent materials absorb certain wavelengths of light and transmit others, the color we see depends on the wavelengths that are transmitted
• The more light that is absorbed, the less light is transmitted and vice versa
Color of opaque objects
• The color an opaque object appears depends on the colors of light it absorbs and reflects.
For example, a red book only reflects red light. It absorbs all the other wavelengths of visible light.
White
light Only red light is reflected
A white hat would reflect all seven colors:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):
Purple light
White
light
White
light
White
light
Using colored light
• If we look at a colored object in colored light we see something different. For example:
White
light
Shorts look blue
Shirt looks red
In different colors of light things would look different:
Red
lightShirt looks red
Shorts look black(Blue shorts absorb red light)
Blue
light
Shirt looks black(Red shirt absorbs blue light
Shorts look blue
Using filters• Filters can be used to “block” out different colors of light:
Red Filter
Magenta Filter