Light Holt chap 13-14

Electromagnetic Spectrum higher frequency higher the energy

Speed of light c = f What is the frequency of an electromagnetic wave if it has a wavelength of 1.0 km? C = speed of light = 3 X 10 8 m/s F = c / = 3 X 10 8 m/s / 1000 m F = 300,000 Hz = 3 X10 5 Hz

Galileo Tried to make a measurement of light by covering and uncovering lanterns and measuring how long it takes for the light to be seen Conclusion: The speed of light is 10 X the speed of sound

Roemer Made the first calculation of the speed of light using data for astronomical observations Roehmer method- measured the time differences of an eclipse of one of Jupiters’s moons to calculate c Conclusion : c = 200,000 km /s

Michelson Used a rotating mirror and plane mirror placed km apart (created better optical equipment to use and used Galileo experiment as a basis) Conclusion: c = X 10 8 m/s

Illuminance E = I / d 2 E = illuminance- lux (lumen/ m 2 ) I= luminous intensity – lumen d = distance – m

Illuminance Example What is the illuminance of a 100 lumen light source that is 50 m away? E = I / d 2 E = 100 lumen / (50 m) 2 E = 0.04 lux

Regular Reflection Law of reflection angle of incidence = angle of reflection If the angle of incidence is 30 o then the angle of reflection is also 30 o

Irregular Reflection EX: Sand, water- this how you get glare and a bad sun burn

Flat mirrors (plane mirrors)

Concave Spherical Mirrors

Images Real Image (di =+) image is upside down and can be projected on a screen Virtual Image (di =-) image is right side up and can not be projected on a screen

Mirror Equation do – object distance (p is often used) di- image distance (q is often used) F- focal length = 1 do di f

Magnification Equation hi- image height ho – object height di- image distance do- object distance Magnification = hi = di ho do

Ray diagrams Concave mirror with the object beyond C

Concave Mirror with the object between C and f

Concave mirror with object between f and the mirror

Convex Mirror

Which picture fits with what ray diagram? Concave Concave Convex Real image virtual virtual image image

EX 1: Concave Mirror - Real Image An object is 3 cm high and is 6 cm away from a concave mirror having a radius of 10cm. A. Where is the image located? B. What is the height of the image? C What type of image is formed and is it right side up or upside down?

EX1: Use the 1/x (x -1 ) key Do = 6 cm f = 5 cm(1/2 the radius) Ho = 5 cm 1 = di f do 1 = di 5 6 di = + 30 cm to the left of the mirror ( beyond the radius or the center of curvature)

EX1: Example of Magnification The term magnification does not mean that the image is necessarily larger hi = di hi = 30 ho do 3 6 hi = 15 cm ( image is larger than object)

EX 1: The image is real because it is positive. The object is upside down and on the same side as the object

EX 2: Concave Mirror - Virtual An object is 3 cm high and is 4 cm away from a concave mirror having a radius of 10cm. A. Where is the image located? B. What is the height of the image? C What type of image is formed and is it right side up or upside down?

EX 2: Use the 1/x (x -1 ) key Do = 4 cm f = 5 cm(1/2 the radius) Ho = 5 cm 1 = di f do 1 = di 5 4 di = -20 cm to the right of the mirror ( “behind” the mirror)

EX 2: Example of Magnification The term magnification does not mean that the image is necessarily larger hi = di hi = - 20 ho do 3 4 hi = - 15 cm ( image is larger than object)

EX 2: The image is virtual because it is negative. The object is right side up and appears in or “behind” the mirror

EX 3:Convex Mirror Problems A pencil is placed 10 cm in front of a convex mirror that has a focal length of 8.00 cm. The pencil is 5 cm high. A.Where if the image formed? B.How tall is the image of the pencil? C.What type of image is formed and is it rightside up or upside down?

EX 3: Use the 1/x (x -1 ) key Do = 10 cm f = - 8 cm Ho = 12 cm 1 = di f do 1 = di di = -4.4 cm to the right of the mirror ( “behind” the mirror)

EX 3: Example of Magnification The term magnification does not mean that the image is necessarily larger hi = di hi = ho do 5 10 hi = cm ( image is smaller than object)

All images from a Convex mirror are virtual The image will be negative and smaller.

Parabolic Mirrors All light converges at focal pt Sperical Aberration - light converges away from focal pt

Color- ROYGBIV

Sir Isaac Newton- light breaks into a light spectrum Spectrum – orderly arrangement of colors after passing through a prism

Seeing color To see a color it must be reflected into your eye If Green is reflected ( all others are absorbed), the you see green White is when all the colors are reflected Black is when all the colors are absorbed

Primary Colors of Light Red, Green and Blue light Mix them together and you get white light

Secondary Light Cyan, magenta and yellow Red yellow Magenta Green CyanBlue

When cyan, magenta and yellow are combined you get black. They are also known as primary pigments

Polarized Light Light normally travels in multiple directions or dimensions Polarized light waves orientated to a particular plane ie: vertical or horizontal Ex: polarized sun glasses

Misc. Vocab Luminous- produces its own light ex: sun Illuminated- reflected light only ex: moon Transparent- can see through clearly ex: clear glass Translucent- cannot see through clearly ex: frosted glass Opaque- cannot see through at all ex: wall

Refraction Bending of a wave as it passes between different substance of different densities

Index of Refraction n = c / v n= index of refraction C = speed of light in a vacuum V = speed of light in medium

Snells Law n- index of refraction I- incidence n i r- refraction  - angle n r n i sin  i = n r sin  r ii rr INDICES OF REFRACTION MEDIUM n VACUUM1.00 AIR1.00 WATER1.33 ETHANOL1.36 CROWN GLASS1.52 QUARTZ1.54 FLINT GLASS1.61 DIAMOND2.42

Optical Density The property of a medium that determines the speed of light in a medium

Example of Snell’s Law A ray of light is incident upon a diamond at 45 o. What is the angle of refraction? n i sin  i = n r sin  r 1 ( sin 45 o ) = 2.42 (sin r) r = 17 o

Lenses Converging light comes together Diverging light spreads

Types of Lenses

Lens Problem Mathematically, done exactly like mirrors Real image is on the right side of the lens Virtual image is on the same side of the lens as the object (left)

Converging Lenses-Real Image Object beyond 2f

Converging Lens- Virtual Image Object is between f and the lens

Diverging Lens

EX: Converging Lens- Real An object is 3 cm high and is 10 cm away from a converging having a focal point of 4 cm. A. Where is the image located? B. What is the height of the image? C What type of image is formed and is it right side up or upside down?

EX: Converging Lens- real Do = 10 cm f = 4 cm Ho = 3 cm 1 = di f do 1 = di 4 10 di = cm to the right side of the lens

EX: Converging Lens- real The term magnification does not mean that the image is necessarily larger hi = di hi = 6.67 ho do 3 10 hi = 2 cm ( image is smaller than object)

EX: Converging Lens- real The image is real because it is positive. The object is upside down and on the right side of the lens

EX: Converging Lens- Virtual An object is 3 cm high and is 4 cm away from a converging having a focal point of 6 cm. A. Where is the image located? B. What is the height of the image? C What type of image is formed and is it right side up or upside down?

EX: Converging Lens- Virtual Do = 4 cm f = 6 cm Ho = 3 cm 1 = di f do 1 = di 6 4 di = -12 cm to the right side of the lens

EX: Converging Lens- Virtual The term magnification does not mean that the image is necessarily larger hi = di hi = -12 ho do 3 4 hi = -9 cm ( image is larger than object)

EX: Converging Lens- Virtual The image is virtual because it is negative. The object is right side up and on the left side of the lens ( same side as object)

Eye

Parts of the Eye Sclera- white part of the eye Iris - colored part of the eye (theorized that it attracts light into the eye) Cornea - clear covering over a pupil Lens – focuses image on retina Retina – contains cells that transform light waves into electrical waves Optic nerve – carries electrical wave to the brain where it is translated

Eye Problems Farsighted -can’t see close up

Color Blindness Red-Green – do not see red or green Blue –Yellow – do not see blue or yellow Monochromatic – see only black and white

Total Internal Reflection Light bounces inside without refracting through the transparent cable

Fiber Optics

Communication- cables Medical- surgery “scopes” Entertainment goods- toys, Xmas trees

Rainbows Refraction- reflection- refraction

Mirages Refraction and reflection

LASER Light Amplification Stimulated Emissions Radiations Monochromatic - one color Coherent – light is parallel Minimum Divergence- light spreads very little