Transcript Ch. 16 Light

Ch. 16
Light
Milbank High School
Sec. 16.1
Light Fundamentals
• Objectives
– Recognize that light is the visible portion of an
entire range of electromagnetic frequencies
– Describe the ray model of light
– Solve problems involving the speed of light
– Define luminous intensity, luminous flux, and
illuminance
– Solve illumination problems
Let there be light!
• Main way we sense our surroundings
• Natural light
– Sun, flames, sparks, fireflies
• Artificial Light
– Bulbs, lamps, TVs, lasers
Light Fundamentals
• Electromagnetic Wave
– Stimulates the retina in the eye
– Wavelengths between 400 and 700nm
• Exact nature not fully understood
– Waves?
– Particles?
• 3.00 x 108 m/s
• c = λf
Ray Model
• Represents a straight-line representation
of light
– Ignores wave properties
– Used to describe how light is reflected and
refracted
Sources of Light
•
•
Luminous body
Illuminated body
•
Luminous flux, P
– lumen, lm
•
Illuminance, E
– lux, lx
Luminous Intensity
• Luminous flux that falls on 1 m2 of a
sphere 1 m in radius
– candela, cd (candle power)
• E = P/4πd2
• E is illuminance
• P is luminous flux
• d is distance from surface
Questions
• How do we know that light travels through
a vacuum?
• What color of visible light has the shortest
wavelength?
• What are the units for:
– Luminous intensity
– Illuminance
– Luminous flux
Sec. 16.2
Light and Matter
• Objectives
– Explain the formation of color by light and by
pigments or dyes
– Explain the cause and give examples of
interference in thin films
– Describe methods of producing polarized light
Light and Matter
• Transparent
– glass
• Translucent
– Lamp shades
– Frosted light bulbs
• Opaque
– bricks
Color
• Spectrum
• Primary Colors
– Red, green, blue
• Secondary Colors
– Yellow, cyan, magenta
– White
• Same intensities of red, green, and blue
Colors Con’t
• Complementary colors
– Yellow made from red and green light
– Yellow + blue = white
– Thus, yellow is the complementary color
Color by subtraction
• Dye
– Molecule that absorbs certain wavelengths of light
and transmits others
– Pigment
• Primary Colors
– Absorbs one primary color from white light
– Yellow, cyan, magenta
• Secondary Colors
– Absorbs two primary colors
– Red, green, and blue
Formation of Colors in Thin Films
• Soap bubble, oily films
• Results of constructive and destructive
interference of light
– Thin-film interference
Polarization
• The intensity of the light is reduced by half
• Light travels in two planes
– Polarizing material cancels out one of the
planes
Review Questions
• What colors does white light consist of?
• Is black a color?
• Why are the insides of binoculars and cameras
painted black?
• You put a piece of red cellophane over one
flashlight and a piece of green cellophane over
another. You shine the light beams on a white
wall. What color will you see where the two
flashlight beams overlap?