Light and Optics

Section 1: Intro to Electromagnetic Waves

• Intro Questions:1. What is the difference between mechanical

and electromagnetic waves?

2. Name as many types of electromagnetic waves you can

3. What is the speed of light and any other electromagnetic wave in space?

5 Min Video (Electromagnetic Waves)

• https://www.youtube.com/watch?v=cfXzwh3KadE

The Electromagnetic Wave

Elec

tric

Fie

ld

Direction of travel towards

you

Magnetic Field

• Characteristics:– Require no medium– Transverse waves of oscillating electromagnetic fields– Transverse waves move perpendicular to the direction the

wave moves– The electric and magnetic fields are at right angles to each

other– All electromagnetic waves travel at 3.0 x 108 m/s

Wavelength Decreases

Frequency Increases

Energy Increases

More Penetration and Dangerous

Velocity = 3.0 x 108 m/sFor All Electromagnetic Waves

V = λ • f3.0 x 108 = λ • f

The Electromagnetic Spectrum

Activity 1

1. Label all the parts of the electromagnetic spectrum in order of increasing frequency.

2. Radio Waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-rays, Gamma Rays

3. Label the trend lines as well

Activity 11. Label all the parts of the electromagnetic spectrum in order of increasing

frequency.2. Radio Waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-rays,

Gamma Rays3. Label the trend lines as well

1 Radio waves

2 Microwaves

3 Infrared

4 Visible Light

5 Ultra Violet 6 X-Rays 7 Gamma Rays

Wavelength Decreases

Frequency Increases

Energy Increases

More Penetration and Dangerous

Section 2: Electromagnetic Wave Math

Speed of light distance-time calculations

• Velocity = 3.0 x 108 m/s for all electromagnetic waves

• If you see any of these you have an electromagnetic wave and v = 3.0 x 108 m/s

• Radio Waves, Microwaves, Infrared, Visible Light, Ultra Violet, X-rays, Gamma Rays

V = λ • f

Example 1

The AM radio band extends from 5.4 x 105 Hz to 1.7 x 106 Hz. What are the longest and shortest wavelengths in this frequency range?

Example 1

The AM radio band extends from 5.4 x 105 Hz to 1.7 x 106 Hz. What are the longest and shortest wavelengths in this frequency range?

Example 2

What is the frequency of an electromagnetic wave if it has a wavelength of 1.0 km?

Example 2

What is the frequency of an electromagnetic wave if it has a wavelength of 2000 m?

Example 3

How long does it take for light from the sun to reach Earth if the sun is 1.5 x 1011 m away?

Example 3

How long does it take for light from the sun to reach Earth if the sun is 1.5 x 1011 m away?

CW/HW

• CP and Honors:• Work on section 1 & 2 of the worksheet

packet

• Honors:• Pg 756 (10,14,15)

Intro

1. What are the primary colors of light?2. List the colors of the rainbow in order3. What do all the colors of the rainbow add up

to?

Section 3: Visible Light and Colors

• Characteristics– “White” light is a combination of red, orange,

yellow, green, cyan, blue, and violet– A prism can separate these colors out• By refraction of different wavelengths of color

Visible Light

Visible Light

Red:• Longest

Wavelength• Lowest

Frequency• Least Energy

Violet:• Shortest

Wavelength• Highest

Frequency• Most Energy

Red orange yellow green cyan blue violet400 nm700 nm

Activity 2• List the colors of the rainbow in order

from lowest to highest frequency• Color this at home

________ ________ ________ ________ ________ ________ ________

VISIBLE LIGHT

Lowest Frequency

HighestFrequency

Activity 2• List the colors of the rainbow in order

from lowest to highest frequency• Color this at home

Red orange yellow green cyan blue violet

VISIBLE LIGHT

Lowest Frequency

HighestFrequency

• Primary Colors– Red– Blue– Green

Red

Blue

Green

• Secondary Colors: Mixture of 2 Primary Colors– Magenta (Blue and Red)

– Cyan (Blue and Green)

– Yellow (Red and Green)

• A mixture of all three primary colors produces white light

Blue

Red Green

Blue

GreenBlue

Green

Red

Red

Magenta

Cyan

Yellow

Blue

White

• Primary Colors– Red– Blue– Green

Red

Blue

Green

• Since secondary colors are a mix of two primaries:

• Mixing primary and secondary colors produces white light

White Light = Primary Color + Secondary Color• White Light = Blue + Yellow• White Light = Green + Magenta• White Light = Red + Cyan

Red

Blue

Green

Activity 3

• Color and label the color mixture diagramWhite Light = Primary Color + Secondary Color

White Light= ___________+ ____________

White Light= ___________+ ____________

White Light= ___________+ ____________

Activity 3

• Color and label the color mixture diagram

White

White Light = Primary Color + Secondary ColorWhite Light = Blue + YellowWhite Light = Green + MagentaWhite Light = Red + Cyan

Primary colors of light

Primary pigments (ink)

Red Blue Green

Magenta Cyan Yellow

• Primary colors (light)– Red– Blue– Green

• Primary pigments (ink)– Magenta– Yellow– Cyan

Red

BlueGreen

Yellow

MagentaCyan

YellowMagenta

Cyan

GreenRed

Blue

are secondary pigments

are secondary colors

Primary colors add up to white light

Primary pigments (ink) adds up to

black

Intro

• Do section 3 of your worksheets as your intro today

Section 4: Refraction of Light

• Optics is the science that describes the behavior and properties of light and the interaction of light with matter.

• Refraction- Bending of light as it travels from one medium to another.

• Refraction occurs because lights velocity changes in another medium.

• Light does not need a medium but it is affected by it.

Key items for refraction• Light travels from the object to the observers

eyes• Light travels at different speed indifferent

medium• Terms to know:– Normal line– Angle of incidence Θi

– Angle of refraction ΘrSlower Medium

Normal Line

Θi

Θr

• As light moves into a new medium, part of it is reflected and part is refracted

• When light moves from a slow to fast medium it refracts bending away from the normal line

• When light moves from a fast to slow medium it refracts bending towards the normal line

Faster: Lower index of refraction (n) valueAir n = 1.0

Slower: Higher index of refraction (n) valueWater n = 1.33

• Objects appear to be in a different position due to refraction– An object “appears” to be straight ahead– Light always travels from the object to the

observers eyes, bending into the new medium

Cats Perspective Fishes Perspective

• Index of refraction (n)- the ratio of speed of light in a vacuum to speed of light in that substance.– Always greater than 1 because light in a vacuum is

the fastest (n = 1.00 for a vacuum)– Has no unit

n = index of refractionc = speed of light in a vacuumv = speed of light in medium

Example 4

• Tom, a watchmaker, is interested in an old timepiece that’s been brought in for a cleaning. If light travels at 1.90 x 108 m/s in the crystal, what is the crystal’s index of refraction?

Example 4• Tom, a watchmaker, is interested in an old timepiece that’s been brought

in for a cleaning. If light travels at 1.90 x 108 m/s in the crystal, what is the crystal’s index of refraction?

Example 5

• How fast does light travel in fluorite (n=1.434)?

Example 5

• How fast does light travel in fluorite (n=1.434)?

• Snell's Law- a formula that describes the angle of incidence and angle of refraction

(ni)(sin Θi) = (nr)(sin Θr)

ni = index of refraction of first medium (incidence side)

Θi = angle of incidence

nr = index of refraction of second medium (refracted side)

Θr = angle of refraction

(ni)(sin θi) = (nr)(sin θr)

Can be rearranged to solve for ni

Can be rearranged to solve for nr

(ni)(sin θi) = (nr)(sin θr)

Can be rearranged to solve for Θi

Can be rearranged to solve for Θr

Example 6

A light ray traveling through air (n=1.00) strikes a smooth, flat slab of crown glass (n=1.52) at an angle of 30.0° to the normal. a. Find the angle of refractionb. Draw a picture and label it

Example 6

• A light ray traveling through air (n=1.00) strikes a smooth, flat slab of crown glass (n=1.52) at an angle of 30.0° to the normal. Find the angle of refraction.

Example 7

Find the angle of refraction for a ray of light that enters a calm lake at an angle of 25° to the normal. (nair = 1.00 and nwater = 1.33)

Example 7

Find the angle of refraction for a ray of light that enters a calm lake at an angle of 25° to the normal. (nair = 1.00 and nwater = 1.33)

Section 5: Critical Angle

• What happens when you increase the angle of incidence when going from a slow to a fast medium?

• Remember: slow to fast bends away from the normal• What happens if you increase the angle of incidence

beyond here?• Total internal reflection

Θi

Θrnr = 1.00 (faster)

ni = 1.33 (slower)

Click on the picture for a critical angle animation

• Critical angle- Angle at which there would be no refraction; only total internal reflection.

• Critical angle equation (θc = critical angle)

Θi

Θrnr = 1.00 (faster)

ni = 1.33 (slower)

Example 8

• A jeweler must decide whether the stone in Mrs. Harder’s ring is a real diamond or a less-precious zircon. He measures the critical angle of the gem and finds that it is 31.3°. Is the stone really a diamond or just a good imitation? (ndiamond = 2.41, nzircon = 1.92, nair = 1.00 )

nair always the smaller n in critical angle problems

n in question: solve for this

Example 8

• A jeweler must decide whether the stone in Mrs. Harder’s ring is a real diamond or a less-precious zircon. He measures the critical angle of the gem and finds that it is 31.3°. Is the stone really a diamond or just a good imitation? (ndiamond = 2.41, nzircon = 1.92, nair = 1.00 )

Intro

Work on section 5 and 6 of your worksheets

Intro1. You are looking at this Red

Pac-Man looking thing in glass (n=1.55) at an angle of 15°. What is the angle of refraction here? (you are in air n=1.00)

Draw a diagram and solve

2. Why can you see a reflection in some materials but not all?

Section 6: Reflection and Intro to Mirrors

• Why can you see a reflection on the surface of one object

• It depends on how smooth the surface isbut not on the surface of another?

L i g ht i s refl e c te d i n t h e s a m e d i re c ti o n h e re

L i g ht i s refl e c te d a l l o ve r h e re

Reflections• Planar reflection -off of a smooth surface

• Diffuse reflection - reflection off of a rough of textured surface. Does not reflect an image

Planar reflection

Diffuse reflection

Intro1. Why cant you see clear reflections on all

surfaces?2. Rough surfaces give a ___________

reflection3. Smooth surfaces give a _____________

reflectionLook at the mirror on your desk look at your reflection on each side4. In what ways is your reflection (image) different on either side of the mirror?

Types of Mirrors

– Plane Mirror – flat mirror– Concave mirror - curved in – the reflecting surface

is inside the sphere– Convex mirror - curved out – the reflecting surface

is outside the sphere

Concave Mirror Convex MirrorPlane Mirror cave

Plane Mirrors

• A plane mirror is a flat mirror• Plane mirrors produce images

that are:– Virtual - image that appears

behind the plane of the mirror.– Upright – Up in the mirror is the

same as the object– Non-magnified – Appear the

same size as if the object was that distance away

– Reversed

Concave (Converging) mirror Produce two types of images depending on where the object is located relative to the focal point• Real inverted images (object beyond focal point)• Magnified virtual upright images (object between focal

point and surface of mirror)

Concave (converging) mirror Why two names?– Concave: name because of shape– Converging: name because of what light does• bends inward or converges

Bends inward toward the object

Convex (diverging) mirror• Only produce virtual, upright, and smaller

images

Convex (diverging) mirror Why two names?– Convex: name because of shape– Diverging: name because of what light does• bends outward or diverges

Bends outward away from the object

• What kind of mirror would water act like?• Why? (What kind of image is formed here)

• What kind of mirror would this be like?• Why? (What kind of image is formed here)

• What kind of mirror would this be like?• Why? (What kind of image is formed here)

Section 7: Planar Ray Diagram

A Ray Diagram• A drawing allows you to determine the size and

orientation of an image formed with a mirror or lens.• The real side of the mirror is the side the object is on

The real side of a mirrorThe virtual side of a mirror

Mirror

Activity 4: Drawing a Ray Diagram in a planar mirror

1. First draw the object, the mirror plane, label p and h. (the object is traditionally drawn as an arrow)• do is the distance to the mirror from the object

• ho is the height of the object

Object

ho

do

Drawing the Rays1. Draw a ray perpendicular to the mirrors surface and include its

reflection2. Draw a single ray going at an angle away from the object to the

mirror (Include its reflection)3. Since the rays don’t cross on the real side of the mirror, after

the reflection, extend them until they meet on the virtual side.4. This is where the image would appear, draw the image, with

the top being where the rays intersect 5. Then finish the labeling

Object

1

23

4ho hi

do di

Variables you need to know• do is the distance to the mirror from the object

• di is the distance from the mirror to the image of the mirror

• ho is the height of the object

• hi is the height of the image

Object Image

ho

do di

hi

Now we can analyze the imageThe image formed in a planar mirror is1. Virtual2. Same size3. Upright

Object

1

23

4

Virtual: on this side of a mirror

ho and hi are equal

Facing up

ho

do di

hi

Example 9

• Law of Reflection Review• Mary sees a reflection of her cat sparkles in the

living room window. The image of Sparkles makes an angle of 40° with the normal, at what angle does Mary see Sparkles reflected?

Θi = 40°

Θr = ?

Example 9

• Law of Reflection Review• Mary sees a reflection of her cat sparkles in the

living room window. The image of Sparkles makes an angle of 40° with the normal, at what angle does Mary see Sparkles reflected?

Θi = 40°

Θr = 40° At 40° to the normal line

Intro

a. __________________ What is line C called above?

b. __________________ What would be the angle or reflection be in the diagram above?

c. __________________ What would be the angle of refraction be in the diagram above?

d. __________________ What would be the critical angle above be for the light beam in a substance(n=1.59) shown above?

Intro

a. __________________ What is line C called above?b. __________________ What would be the angle or reflection be in the

diagram above?c. __________________ What would be the angle of refraction be in the

diagram above?

d. __________________ What would be the critical angle above be for the light beam in the substance (n=1.59) shown above?

Section 8: Concave Mirror Ray Diagram

Curved Mirror Ray Diagram• More variables you need to know for a curved

mirror– Center of curvature (C) – the center of the curve if

it was a sphere– Focal Point (F) – ½ from the mirror to the center

of curvature– Principal axis- the line that the base of the arrow

is on.

C FPrincipal axis

C F

Rules for Drawing Reference Rays (Concave Mirror)

Ray Line drawn from object to mirror

Line drawn from mirror to image after reflection

1. Parallel to principal axis Through focal point F

2. Through focal point F Parallel to principal axis

The image appears where all rays intersect

Activity 5

object

image

• Now analyze the image just formed• Its:– Smaller (hi is less than ho)– Inverted (upside down)– Real (on the object side of a mirror)

ho

hi

Activity 5

• A concave mirror produces many different types of images

• Click picture for concave mirror animation

C F

Rules for Drawing Reference Rays (Concave Mirror)

Ray Line drawn from object to mirror Line drawn from mirror to image after reflection

1. Parallel to principal axis Through focal point F

2. Through focal point F Parallel to principal axis

The image appears where all rays intersect

Activity 5

object

image

• Now analyze the image just formed• Its:– Not magnified (ho = hi)– Inverted (upside down)– Real (on the object side of a mirror)

hoC F

Activity 5

C F

Rules for Drawing Reference Rays (Concave Mirror)

Ray Line drawn from object to mirror Line drawn from mirror to image after reflection

1. Parallel to principal axis Through focal point F

2. Through focal point F Parallel to principal axis

The image appears where all rays intersect

Activity 5

object

image

• Now analyze the image just formed• Its:– magnified (ho < hi)– Inverted (upside down)– Real (on the object side of a mirror)

C F

ho

hi

Activity 5

C F

Rules for Drawing Reference Rays (Concave Mirror)

Ray Line drawn from object to mirror Line drawn from mirror to image after reflection

1. Parallel to principal axis Through focal point F

2. Through focal point F Parallel to principal axis

Activity 5

• Now analyze the image just formed• Its:– No image formed– Does not intersect on the real or virtual side

C F

Activity 5

C F

Rules for Drawing Reference Rays (Concave Mirror)

Ray Line drawn from object to mirror Line drawn from mirror to image after reflection

1. Parallel to principal axis Through focal point F

2. Through focal point F Parallel to principal axis

Activity 5

object

• Now analyze the image just formed• Its:– magnified (ho < hi)– upright– Virtual (on the virtual side of a mirror)

C F

image

hiho

Activity 5

Section 9: Convex Mirror Ray Diagram

Rules for Drawing Reference Rays (convex mirror)

Ray Line drawn from object to mirror

Line drawn from mirror to image after reflection

1. Parallel to principal axis Through focal point F (away from the mirror)

2. Through focal point F Parallel to principal axis

3. Follow the arrow tips away from the mirror back with virtual lines until they intersect

CF

This is where the image appearedActivity 6

• Now analyze the image just formed• Its:– Smaller (hi is less than ho)– Upright– Virtual (on the other side of a mirror)– A convex mirror always produces this type of

image

This is where the image appeared

WS

• Work on section 7-9 problems 1,2,3,4• Go back and work on anything incomplete

from the worksheet packet when you are done

Intro• Do the following ray diagrams:

• 1.

• 2.F

F C

C

3. List the objects that arePlane Mirrors

Concave Mirror

Convex Mirrors

Section 10: Mirror Math

Lens/ Mirror Math Cheat SheetTake out a piece of paper and copy all of this

+ Real imageor

- Virtual image

+ Real imageor

- Virtual image

Mirror Math Equations

If M is negative then the image is inverted

• The object side is always positive for lenses and mirror math

• The image sign depends on image location• The image here would have a positive value• The image here would have a negative value

Positive object sidePositive image side of mirror

do di

di

Positive focal side of mirror

• The focus is on the side of the center of curvature

• The concave mirror always curves to the real side and has a positive F

Positive focal side of mirror

F

• The focus is on the side of the center of curvature

• The convex mirror always curves to the virtual side and has a negative F

Positive focal side of mirror

F

Example 10

A concave mirror has a focal length of 10.0 cm. Locate the image of a pencil that is placed upright 30.0 cm from the mirror. a. Find the magnification of the image.b. Draw a ray diagram of the situation

FC

Example 10• A concave mirror has a focal length of 10.0 cm.

Locate the image of a pencil that is placed upright 30.0 cm from the mirror.

a. Find the magnification of the image.

Example 10

A concave mirror has a focal length of 10.0 cm. Locate the image of a pencil that is placed upright 30.0 cm from the mirror. b. Draw a ray diagram of the situation

FC

Example 11

Mark is polishing his crystal ball. He sees his reflection as he gazes into the ball from a distance of 15 cm.a. what is the focal length of Mark’s crystal ball

if he sees her reflection 4.0 cm behind the surface?

b. Is the image real or virtual

Example 11Mark is polishing his crystal ball. He sees his reflection as he gazes into the ball from a distance of 15 cm.a. what is the focal length of Mark’s crystal ball if he sees her reflection 4.0 cm

behind the surface?b. Is the image real or virtual

Example 12

You look into an empty water bowl from 6.0 cm away and see a reflection 12 cm behind the bowl. a. What is the focal length of the bowl?b. What is the magnification of the image?

Example 12• You look into an empty water bowl from 6.0 cm away and see a reflection

12.0 cm behind the bowl. a. What is the focal length of the bowlb. What is the magnification of the image?

Section 11: Intro to Lenses

• Mirrors work because they reflect light.• Lenses work because they refract light.

Types of lenses

• Convex (converging) lens• Concave (diverging) lens

A magnifying glass is a convex lens also called a converging lens

Convex (converging) LensWhy two names?– Convex: name because of shape– converging: name because of what light does• bends inward or converges

Near side bends outward away from the object

Concave (diverging) LensWhy two names?– Concave: name because of shape– Diverging: name because of what light does• bends outward or diverges

Near side bends inward toward the object

The Lens• do – distance to object

• di – distance to image

• ho – height of object

• hi – height of image• F’ – virtual focal point• 2F’ – double virtual focal point• F – focal point• 2F – double focal point

ObjectImage

di

ho

hiReal side in lensesVirtual side in lenses

F’ F

2F

2F’

do

Section 12: Concave Lens Ray Diagram

Rules for Drawing Reference Rays (concave/diverging lens)

Ray Line drawn from object to lens Line drawn from mirror to image after refraction

1. Parallel to principal axis Through focal point F’

2. Through center of lens Continue straight

3. Follow the arrow tips back to the virtual side where they intersect

F’ F 2F2F’

The image appears where all rays intersect

Activity 7

Concave/diverging lens• Always produces a:– Virtual– Upright– Smaller image

Section 13: Convex Lens Ray Diagram

F’ F

2F

2F’

Rules for Drawing Reference Rays (convex/converging lens)

Ray Line drawn from object to lens Line drawn from mirror to image after refraction

1. Parallel to principal axis Through focal point F

2. Through center of lens Continue straight

3. Place the image head where the rays intersect or trace the rays to the virtual side if they don’t intersect

Activity 8

Convex/converging lens• Image produced:– Outside focal point (F’):• Real and inverted• Outside 2F’: smaller• At 2F’: same size• Between 2F’ and F’: magnified

– Inside focal point (F’)• Virtual and upright

F

F’

CW/HW

• Do section 11-13 lens ray diagrams

Section 14: Lens Math

Intro

1. Label the real(+) and virtual(-) side of this lens2. Draw the ray diagram and describe the image

F’ F

Lens Math

• The object side is always positive for lenses and mirror math

• The virtual and real image sides are different for lenses• The other side of the lens is positive for the image– The image here would have a positive value– The image here would have a negative value

Positive object side

Negative image side Positive image side of lens

do

di

di

do

• To determine the sign of the focal point• Determine which way the front of the lens curves

or just remember these two facts:– A convex lens always has a positive focal length• Curves to the real side of a lens

– A concave lens always has a negative focal length• Curves to the virtual side of a lens

Negative image and focal side of lens

Positive image and focal side of lens

Example 13

An object is placed 5.00m away from a convex lens which produces a real image 1.00 awaya. What is the focal length of the lens?b. Draw a ray diagram of the situation

F’ F

Example 13When Sally holds a convex lens 1.00 m from a snow-covered wall, an image of a 5.00 m distant igloo is projected onto the snow.a. What is the focal length of the lens?

Example 13

When Sally holds a convex lens 1.00 m from a snow-covered wall, an image of a 5.00 m distant igloo is projected onto the snow.b. Draw a ray diagram of the situation

F’ F

Example 14A concave lens is placed 5.0 cm in front of a doll.a) What is the focal length of the lens if the doll’s

image appears 2.0 cm on the same side of the lens?b) Draw a ray diagram of the situation

F’ F

Example 14A concave lens is placed 5.0 cm in front of a doll.a) What is the focal length of the lens if the doll’s

image appears 2.0 cm on the same size of the lens?

Example 14A concave lens is placed 5.0 cm in front of a doll.a) What is the focal length of the lens if the doll’s

image appears 2.0 cm on the same size of the lens?b) Draw a ray diagram of the situation

F’ F

Example 15

A coin collector is looking at a rare coin 1.0 cm behind a magnifying glass (convex lens) with a focal length of 5.0 cm. a. What is the distance to the image?b. What is the image’s magnification?

Example 15

A coin collector is looking at a rare coin 1.0 cm behind a magnifying glass (convex lens) with a focal length of 5.0 cm. a. What is the distance to the image?

Example 15

A coin collector is looking at a rare coin 1.0 cm behind a magnifying glass (convex lens) with a focal length of 5.0 cm. a. What is the distance to the image?b. What is the image’s magnification?

-

CW/HW

• Do section 14 of the worksheet packet

Intro1. You are looking at yourself from 5cm away in a concave

mirror that has a focal length of 15cm. A. What is the distance to the image?B. What is the magnification?

2. You do the same as in #1 but in a convex mirrorC. What is the distance to the image?D. What is the magnification?

3. You are looking through a convex lens at an object 5cm away. The image is projected 15 cm on the same

E. What is the focal length of the lens?F. What is the magnification?

Intro1. You are looking at yourself from 5cm away in a concave

mirror that has a focal length of 15cm. A. What is the distance to the image?B. What is the magnification?

Intro2. You do the same as in #1 but in a convex mirror

A. What is the distance to the image?B. What is the magnification?

Intro3. You are looking through a convex lens at an object 5cm

away. The image is projected 15 cm on the same A. What is the focal length of the lens?B. What is the magnification?

4. A ray of light is coming from a penny at the bottom of the water and hitting the surface at an angle of 34ᵒ what is the angle of refraction. (nair =1.00 nwater =1.33)

4. A ray of light is coming from a penny at the bottom of the water and hitting the surface at an angle of 34ᵒ what is the angle of refraction. (nair =1.00 nwater =1.33)

4. A ray of light is coming from a penny at the bottom of the water and hitting the surface at an angle of 34ᵒ what is the angle of refraction. (nair =1.00 nwater =1.33)

Section 15: Common Optical Instruments

Common Optical Instruments• Camera- A simple camera consists

of a convex lens and a light sensitive film

• The diaphragm and shutter regulates how much light gets to the film.

• The diaphragm controls the size of opening the light passes through

• Most cameras use more than one lens today

Common Optical Instruments• Telescope- Uses two lenses to enlarge an

image far away.

• You see an image of an image. The eyepiece lens forms an enlarged virtual image of the real image formed by the objective lens.

The Eye• How the eye focuses:

– The ciliary muscle around the eye changes the shape and thickness of the lens, which changes the focal length of the lens

– In both cameras and the eye the image is inverted. The brain has learned to turn the image around.

Defects in Vision

• Farsighted (Hyperopia)- trouble focusing on objects close. The eyeball is too short or the cornea is too flat. – Focus is behind the retina without correction

Defects in Vision

• Nearsighted (Myopia)- trouble focusing on objects far away. The eyeball is too long or the cornea is too curved.

• Focus is in front of the retina

Fixing defects• Converging/convex lenses are used to correct

farsightedness.

• Diverging/concave lenses are used to correct nearsightedness.

Section 15: Dual Nature of Light

Dual Nature of LightWave Particle Duality

• Light acts as a wave (through space) and a particle (when it interacts with matter)

– Waves are energy carried in the disruption of medium. Have interference patterns when they go through each other.

– Particles have a mass and could not occupy the same space.

Remember Interference

• Within an interference pattern wave amplitudes may be increased, decreased, or neutralized

Constructive Interference Causes Reinforcement

Destructive Interference Causes Cancelation

Interference with Waves in Water

• Reinforcement and cancelation can be seen here

• Huygens Principle– Huygens states light acts as a wave– Every point acts as a source of a new wave

Wave Properties of Light

• Single slit diffraction on visible light.• Light has Huygens property of a wave• Light fans out and actually appears wider than

it should be.

Young’s Interference Experiment

• Young further demonstrate the wave properties of light with a double slit film.

• When a monochromatic light source is used a pattern of fringes result

• Young shows that light has interference based on its wave properties

Particle Nature of Light• Light acts like a stream of particles when it

interacts with matter

• Photoelectric Effect- Ejection of electrons from certain metals when light falls upon them.– Requires a high frequency of light

Dual Nature of Light Video Clip

Section 16: Other Light Phenomenon

Laser Light• Incoherent light- crests and troughs don’t line

up

• Coherent light- crests and troughs line up (same frequency, phase, and direction)

• Laser- Produces coherent light with the aid of a crystal

Laser Light

Light sabers and Laser beams

Rainbows are produced by the refraction of light

Thin Films

• Light from one side of a bubble cancels out light from the other side showing color from white light

• Diffraction Grating can be used to disperse light into colors like a prism– A prism used refraction to disperse light– Diffraction gradients use the interference of light

to produce colors

Diffraction and Polarization Clip

Polarization of Light

• Light is an electromagnetic wave• These waves produce an electric field at a

right angle to the magnetic field• Usually the rays are unpolarized which means

they are oscillating in random directions.

Polarized Light• Some crystals can cause unpolarized light to

pass through and produce polarized light which has its electromagnetic fields aligned in the same direction.

• Transmission axis- line along which light is polarized

• Transmission axis- line along which light is polarized

• Light at 90º to the transmission axis cannot pass through.

How polarized sunglasses work• Glare– When light reflects off the ground (a horizontal

surface) it is polarized horizontally.• Sunglasses stop glare– They are polarized vertically so that horizontal glare

cannot get through