Light Holt 2006- chap 13-14. Electromagnetic Spectrum higher frequency higher the energy

Light

Holt 2006- chap 13-14

Electromagnetic Spectrumhigher 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 X105 Hz

Galileo

• 1667- 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• 1675 -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 = 2.997924562 X 10 8 m/s

Illuminance E = I / d2

• E = illuminance- lux (lumen/ m2)• 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 / d2

E = 100 lumen / (50 m)2

E = 0.04 lux

Regular Reflection

Law of reflection angle of incidence = angle of reflectionIf the angle of incidence is 30o then the angle of

reflection is also 30o

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 + 1 = 1

do di f

Magnification Equation

hi- image height

ho – object height

di- image distance

do- object distance

Magnification = hi = di

ho do

Ray diagramsConcave 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 = 1 - 1 di f do

1 = 1 - 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 cm1 = 1 - 1

di f do

1 = 1 - 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 cmHo = 12 cm

1 = 1 - 1 di f do

1 = 1 - 1 di -8 10

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 = - 4.4

ho do 5 10

hi = - 2.2 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

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 Cyan Blue

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 ni

r- refraction

- angle nr

ni sin i = nr sin r

i

rINDICES OF REFRACTION

MEDIUM n

VACUUM 1.00

AIR 1.00

WATER 1.33

ETHANOL 1.36

CROWN GLASS 1.52

QUARTZ 1.54

FLINT GLASS 1.61

DIAMOND 2.42

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 45o. What is the angle of refraction?

ni sin i = nr sin r

1 ( sin 45o) = 2.42 (sin r)

r = 17o

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 cmHo = 3 cm

1 = 1 - 1 di f do

1 = 1 - 1 di 4 10

di = + 6.67 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 cmHo = 3 cm

1 = 1 - 1 di f do

1 = 1 - 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

Fiber Optics

• Communication- cables

• Medical- surgery “scopes”

• Entertainment goods- toys, Xmas trees

Rainbows• Refraction- reflection- refraction

Mirages

• Refraction and reflection

LASERLight Amplification Stimulated Emissions Radiations

• Monochromatic - one color

• Coherent – light is parallel

• Minimum Divergence- light spreads very

little