Physical Science Light and Optics Slides subject to change

Electromagnetic Spectrum

Speed of Light Light in vacuum: c = 299,792,458 meters/second Mt Wilson to Lookout Mountain (adjacent to Mt Baldy) First modern and truly accurate measurement of this fundamental physical constant. Albert Michelson’s measurements in 1926: 299,796 ±4 km/s. Michelson

Mt Wilson Mt Wilson Mt Baldy, Lookout Mountain Mt Baldy, Lookout Mountain 22 Miles

Light Ray A light ray is a straight line that represents one path of light. A light ray is a straight line that represents one path of light. Ray concept is used to study path of light. Ray concept is used to study path of light. A “ray” Incoming waves Outgoing, reflected, waves Reflecting surface

Reflection Angle of reflection equals angle of incidence. θ r = θ i Angle of reflection equals angle of incidence. θ r = θ i Specular reflection: Smooth surface... mirror, car finish. Specular reflection: Smooth surface... mirror, car finish. Diffuse reflection: Rough surface... wall, highway. Diffuse reflection: Rough surface... wall, highway. θiθiθiθi θrθrθrθr

Wall Mirror Object Image A Virtual Image... There is really no light energy behind the mirror. A human eye focuses on the image behind the mirror... but it is looking at reflections. Eye focus

Refraction Incident ray Small Reflected ray Refracted ray Air Some Transparent Medium e.g., Glass or Water A ray bends towards the vertical as it enters a slower medium. The slower the medium, the more it bends.

Index of Refraction Light rays bend because of a change in light speed. Light rays bend because of a change in light speed. Index of refraction n. Index of refraction n. Water: n water = 1.3 Water: n water = 1.3 Glass: n glass = 1.5 Glass: n glass = 1.5 Diamond: n diamond = 2.4 Diamond: n diamond = 2.4

Refraction Incident ray Air Water n = 1.3 Ghost coin seems to be out here refraction video refraction video

Speed of Light What is the speed of light in water? What is the speed of light in water? GivenFormula c = 3x10 8 m/s v = c/n c = 3x10 8 m/s v = c/n n water = 1.3 n water = 1.3 v water = (3x10 8 )/1.3 v water = (3x10 8 )/1.3 = 2.3x10 8 m/s

Speed of Light What is the speed of light in a diamond (in miles per second)? What is the speed of light in a diamond (in miles per second)? n diamond = 2.4 n diamond = 2.4 c = 186,000 mi/s c = 186,000 mi/s v diamond = (186,000)/2.4 v diamond = (186,000)/2.4 = 77,000 mi/s (pokes along about 100,000 miles/s slower than in a vacuum.)

Total Internal Reflection Total Internal reflection. Total Internal reflection. Totally reflected ray. Totally reflected ray. No energy escapes. No energy escapes. Source of ray is in the medium Normal refraction Normal refraction

Fiber Optic Communications Transmit communication signals by total internal reflection. Transmit communication signals by total internal reflection. High data rates, low energy loss. High data rates, low energy loss. Immune to interference. Immune to interference. Long distance glass fiber paths with repeaters every miles. Long distance glass fiber paths with repeaters every miles. Minimal light escapes. Minimal light escapes.

Diamonds Design diamonds for maximum return of all colors—total internal reflection. Design diamonds for maximum return of all colors—total internal reflection. Cut is the most important quality factor, and most challenging. The brilliance of a diamond depends heavily on its cut. Cut is the most important quality factor, and most challenging. The brilliance of a diamond depends heavily on its cut.

Images Images are real if light goes through them. For example, a real image can be formed on a screen. Images are real if light goes through them. For example, a real image can be formed on a screen. Images are virtual if no energy goes through them, where the image appears to converge, such as an image in a wall mirror. Images are virtual if no energy goes through them, where the image appears to converge, such as an image in a wall mirror.

A Virtual Image in a Mirror Virtual Image There is really no light energy behind the mirror. Wall mirror, no focal point (focus is at infinity).

Spherical Lenses Convex lens Convex lens “Converging lens.” “Converging lens.” Concave lens Concave lens “Diverging lens.” “Diverging lens.”

Converging Lens Parallel rays bend towards the focus. Parallel rays bend towards the focus. Ray through center goes straight through. Ray through center goes straight through. Where they cross is the image of the tip of the arrow head. Where they cross is the image of the tip of the arrow head. Convex lens, with object distance greater than focal distance gives a real, inverted image. Convex lens, with object distance greater than focal distance gives a real, inverted image. This is a “real” image

Converging Lens Suppose all the rays are parallel (e.g., from the Sun) Suppose all the rays are parallel (e.g., from the Sun) Intense heat and light at the “focal point.”

Converging Lens A “Magnifying Glass” A “Magnifying Glass” Your eyes focus on large image under the magnifying glass. Your eyes focus on large image under the magnifying glass. ObjectImage Look this way

Human Eye First lens: the cornea. 80% of refraction at air-cornea interface. n = First lens: the cornea. 80% of refraction at air-cornea interface. n = About the thickness of a dime. About the thickness of a dime. Near-sighted - focus inside eye before the retina. Near-sighted - focus inside eye before the retina. Far-sighted - focus behind the eye. Far-sighted - focus behind the eye.

Human Eye Second lens: 20% of refraction. n ~ 1.4. Second lens: 20% of refraction. n ~ 1.4. Crystalline lens is pliable, its thickness adjusted by ciliary muscles. Crystalline lens is pliable, its thickness adjusted by ciliary muscles. Like a transparent onion, ~ 22,000 layers. Like a transparent onion, ~ 22,000 layers. Crystalline lens less pliable with age. When crystalline lens clouds or darkens, it’s called a cataract. Crystalline lens less pliable with age. When crystalline lens clouds or darkens, it’s called a cataract.

LASIK Surgery Open a small flap on surface of cornea. Open a small flap on surface of cornea. Remove microscopic amounts of corneal tissue with ultraviolet laser. Painless. Remove microscopic amounts of corneal tissue with ultraviolet laser. Painless. Either flatten the cornea to treat nearsightedness, or steepen the cornea to treat farsightedness, or make the cornea more spherical to treat astigmatism. Either flatten the cornea to treat nearsightedness, or steepen the cornea to treat farsightedness, or make the cornea more spherical to treat astigmatism.

Polarization Transverse waves can be aligned so tranverse motion is along one axis. Transverse waves can be aligned so tranverse motion is along one axis. Specially processed plastic useful for light polarization. “Polaroid.” (Edwin H. Land 1929.) Specially processed plastic useful for light polarization. “Polaroid.” (Edwin H. Land 1929.) Reflected light is polarized, Polaroid sunglasses cut down glare. Reflected light is polarized, Polaroid sunglasses cut down glare. Internet Encyclopedia of Science

Diffraction A wavefront curves in concentric arcs as it emerges from an opening. A wavefront curves in concentric arcs as it emerges from an opening. As the barrier or opening size gets smaller and closer to the wavelength, the wavefront experiences more and more curvature. As the barrier or opening size gets smaller and closer to the wavelength, the wavefront experiences more and more curvature.

Single Slit Diffraction Wave crests

Two-Slit Interference Lines where crests add to to make a stronger signal (constructive interference) seem to form a pattern. Lines where crests add to to make a stronger signal (constructive interference) seem to form a pattern. Wave crests Strong Signal →

Two-Slit Interference Lines where crests add to to make a stronger signal (constructive interference) seem to form a pattern. Lines where crests add to to make a stronger signal (constructive interference) seem to form a pattern. Sound Waves Sound Waves Sound Waves Sound Waves

Two-Slit Interference

Spherical Mirrors Convex mirror. Convex mirror. “Diverging mirror.” “Diverging mirror.” Concave mirror (“caved in”). Concave mirror (“caved in”). “Converging mirror.” “Converging mirror.” Follow the rays from the tip of the arrow. Follow the rays from the tip of the arrow.

Concave Mirrors Ray toward the center reflects. Ray toward the center reflects. f = focal point Parallel ray along principal axis reflects through focal point. Parallel ray along principal axis reflects through focal point. Object

Convex Mirrors Image is small and upright. Image is small and upright. Ray reflects off, in line with the focal point behind the mirror.

Convex Mirrors Image is small and upright. Image is small and upright. To a person’s eyes, the smaller object looks farther away than the it really is. To a person’s eyes, the smaller object looks farther away than the it really is. Therefore “Objects in mirror are closer than they appear.” Therefore “Objects in mirror are closer than they appear.” Ray reflects off, in line with the focal point behind the mirror.

Concave Mirrors Object Where the rays cross is the focused real image of the tip. Where the rays cross is the focused real image of the tip.