Electro- magnetic Waves

Electromagnetic Waves Waves consisting of oscillating electric and magnetic fields that move at the speed of light through space.

Electromagnetic Spectrum Corresponding wavelength and frequency

Light Light is the range of frequencies of the electromagnetic spectra that stimulate the retina of the human eye.

Wavelengths of Light Range from: 400 nm to 700 nm m to m

Speed of Light The story starts with: Galileo Galilei First to hypothesize that light has a finite speed (1564 – 1642)

The story takes off with: Ole Roemer (1644 – 1710) Determined the relative speed of light by viewing the orbital period of Io, a moon of Jupiter. The period varied by 14 seconds, depending on the Earths approach. Jupiter Earth Orbit From this he calculated it took 22 minutes for light to travel across the orbit of the Earth. Today’s accepted value is about 16 minutes

Jump to the twentieth century: Albert Michelson (1852 – 1931) In 1926 Michelson was working at the Mount Wilson Observatory in Pasadena California, when he calculated the time light required to make a round trip between two California Mountains 35 Km apart. Determined the speed of light to be: First American to receive the Nobel Prize

Sources of Light Luminous Bodies – Objects that emit light waves. i.e. - Sun Illuminated Bodies – Objects that reflect light waves. i.e. - Moon Luminous Flux - P – Rate at which light is emitted from a source in all directions. Units Lumen = lm Illuminance – E – Measure of the illumination of a surface. Units Lux = lx Lumens per square meter Candela – cd – Candle Power – Measure of luminous intensity

Sources of Light The Luminous Intensity of a point source is the Luminous Flux that falls on one square meter of a sphere one meter in radius. Thus Luminous Intensity is Luminous Flux divided by 4 Illuminance varies directly with the flux of the light source and inversely with the square of the distance from the source. measured in cd

Transparent Light waves are transmitted through the material Translucent Material that transmits light but distorts the path Opaque Material that does not transmit light

Refraction of Light Refraction – The change in direction or bending of light waves at the boundary between two media. Snell’s Law – A ray of light bends in such a way that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. For a light ray passing from a vacuum into a given medium. This constant n is the index of refraction For two media other than a vacuum

Refraction of Light Indices of Refraction Medium n Vacuum1.00 Air Water1.33 Ethanol1.36 Lucite Plastic1.49 Crown Glass1.52 Quartz1.54 Flint Glass1.61 Diamond2.42 The Larger the index of refraction the greater bending of light

Color is perceived because of a physiological response to excitation by light of the cone receptors in the retina of the human eye. The cones are sensitive to light with wavelength of 400 nm to 700 nm. Different wavelengths of light are perceived by the brain as different colors. Primary Light Colors RED BLUE GREEN Secondary Light Colors MAGENTA CYAN YELLOW

Additive Method of Color Production When light beams of the primary colors (red, blue and green) are projected onto a white screen,, mixtures of them produce other colors. Varying the intensities of the beams allows different colors to be produced. Red + Green = Yellow Green + Blue = Cyan Blue + Red = Magenta Red + Green + Blue = White Hyper Link->

Complementary Colors = Two colors that, when added produce white light Yellow + Blue = White Magenta + Green = White Cyan + Red = White Pigments are colored material that absorb certain colors and transmit or reflect others Example – A tomato absorbs blue and green light and reflects red light, so it appears red. If only blue light was projected on the tomato it would appear black

A pigment that absorbs only one color from white light is called a Primary Pigment Primary Pigments = Yellow, Cyan and Magenta Example: A banana absorbs blue light and reflects green and red, so it looks yellow A Pigment that absorbs two primary colors and reflect one is a Secondary Pigment Note that the primary pigment colors are the secondary light colors and the secondary pigment colors are the primary light colors. Example: The Jolly Green Giant appears green because he absorbs both blue and red light and reflects green light Secondary Pigments = Red, Blue and Green

Polarization Orientation of the transverse oscillations of light waves Partially Polarized – Some preferential orientation Plane or Linearly Polarized – Orientation in only one plane