16.1  Light Fundamentals Visible light is part of a very broad range of frequencies called

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16.1 – Light Fundamentals Visible light is part of a very broad range of frequencies called The Electromagnetic Spectrum. Visible light ranges from 700 nm to 400 nm

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16.1 – Light Fundamentals

Visible light is part of a very broad range of frequencies called

The Electromagnetic Spectrum.

Visible

light

ranges

from

700 nm

to

400 nm

ROYGBIV

Radio – microwaves – infrared – visible – ultraviolet – x rays – Gamma rays.

Longer wavelength Shorter Wavelength

Lower freq, Lower energy (E=h.f) Higher Freq, High Energy

Speed of light, c = 3x108 m/s

C = λ.f

E/M radiation follows the inverse-square law

Roemer - determined in 1670

- Careful measurement of period of Io. 14 sec longer period

when earth moving away, 14 sec faster than towards.

By 1676 figured it took 22 min to cross earth’s diameter.

Came up with 220,000,000m/s, ~ 3/4 present value.

By 1926 measuring time between 2 mtns, at 2.997996x108 m/s.

Transparent- Materials light passes thru undistorted

Translucent- light passes thru distorted

Opaque- Light cannot pass thru

*White light is made up of all wavelengths of visible light: ROYGBIV

-It can be separated by a prism or by Filters.

Primary colors of light:

RED GREEN BLUE

Primary pigment colors:

CYAN MAGENTA YELLOW

-pigments absorb colors of light

Ex1) Magenta: Reflects ______,______ absorbs _______

Cyan: Reflects _____,______ absorbs ______

Yellow: Reflects ______,______ absorbs ______

Red paint: Reflects _______ absorbs ______,______

Complimentary colors – add together to form white light.

Ex2) Comp. to magenta is ______

Comp. to red is ______

Comp. to yellow is ______

Ch16 HW#1 1-11

Lab16.1 – Light Intensity

- due tomorrow

- go over Ch16 HW#1 at beginning of period

Chapter 16, HW#1

1. What is the frequency of yellow light if the wavelength is 556nm?

2. What is the wavelength of red light if its frequency is 4.28 x 1014 Hz?

3. Convert 700nm, the wavelength of red light, to meters

4. The sun is 1.5x1011 m from Earth. How long does it take for

the sun’s light to reach us?

5. The distance to the moon can be found with the help of mirrors left on

the moon by astronauts. A pulse of light is sent to the moon and returns to Earth in 2.562s. Using the defined speed of light, calculate the distance from Earth to the moon.

Chapter 16, HW#1

1. What is the frequency of yellow light if the wavelength is 556nm?

2. What is the wavelength of red light if its frequency is 4.28 x 1014 Hz?

3. Convert 700nm, the wavelength of red light, to meters.

700nm = 0.000000700m = 7x10-7m

4. The sun is 1.5x1011 m from Earth. How long does it take for

the sun’s light to reach us?

5. The distance to the moon can be found with the help of mirrors left on

the moon by astronauts. A pulse of light is sent to the moon and returns to Earth in 2.562s. Using the defined speed of light, calculate the distance from Earth to the moon.

d = v.t = (3x108m/s)(2.562sec)=

6. The intensity of light at a distance of one meter from a 100 W light bulb

is 140 lux. (What the lux you ask? Well it’s the amount of luminous flux

per square meter, of course! Since that doesn’t probably make any sense to you, don’t worry about the units. Just answer this question:)

What would be the intensity at a distance of 2 meters?

7. A red apple is red because it absorbs what primary color(s) of light,

and reflects what primary color(s) of light?

8. My school colors were cyan and magenta. If you are looking at

the magenta color on the school building, what color(s) are being

absorbed? What color(s) are being reflected?

How about with the cyan color – what’s absorbed

and what’s reflected?

6. The intensity of light at a distance of one meter from a 100 W light bulb

is 140 lux. (What the lux you ask? Well it’s the amount of luminous flux

per square meter, of course! Since that doesn’t probably make any sense to you, don’t worry about the units. Just answer this question:)

What would be the intensity at a distance of 2 meters?

Inverse square law: double distance = 4X less light = 35 lux

7. A red apple is red because it absorbs what primary color(s) of light,

and reflects what primary color(s) of light?

Red absorbs blue, green, reflects red.

8. My school colors were cyan and magenta. If you are looking at

the magenta color on the school building, what color(s) are being

absorbed? green What color(s) are being reflected? blue,red

How about with the cyan color – what’s absorbed red

and what’s reflected? blue,green

mix to make a blue pigment?

10. You put a piece of red cellophane over one flashlight and a piece

of green cellophane over another flashlight. You shine the light beams

on a white wall. What color will you see where the two flashlight beams overlap?

11. You now put both the red and green cellophane pieces over one

flashlight. If you shine the flashlight beam on a white wall, what color will

you see?

mix to make a blue pigment?

Mix cyan and magenta

10. You put a piece of red cellophane over one flashlight and a piece

of green cellophane over another flashlight. You shine the light beams

on a white wall. What color will you see where the two flashlight beams overlap?

11. You now put both the red and green cellophane pieces over one

flashlight. If you shine the flashlight beam on a white wall, what color will

you see?

mix to make a blue pigment?

Mix cyan and magenta

10. You put a piece of red cellophane over one flashlight and a piece

of green cellophane over another flashlight. You shine the light beams

on a white wall. What color will you see where the two flashlight beams overlap? red + green = yellow

11. You now put both the red and green cellophane pieces over one

flashlight. If you shine the flashlight beam on a white wall, what color will

you see?

mix to make a blue pigment?

Mix cyan and magenta

10. You put a piece of red cellophane over one flashlight and a piece

of green cellophane over another flashlight. You shine the light beams

on a white wall. What color will you see where the two flashlight beams overlap? red + green = yellow

11. You now put both the red and green cellophane pieces over one

flashlight. If you shine the flashlight beam on a white wall, what color will

you see? red doesn’t allow blue or green

green doesn’t allow blue or red

= nothing gets thru: black

Ch16.2 – Reflection, Diffraction, Polarization

Reflection:

Θi Θr

Law of Reflection:

Angle of Incidence = Angle of Reflection

Θi = Θr

Ex1) A light ray strikes a mirror at a 53˚ angle to the normal.

A. What is the angle of reflection?

B. What angle does the incident ray make with the reflected ray?

Ch16.2 – Reflection, Diffraction, Polarization

Reflection:

Θi Θr

Law of Reflection:

Angle of Incidence = Angle of Reflection

Θi = Θr

Ex1) A light ray strikes a mirror at a 53˚ angle to the normal.

A. What is the angle of reflection? 53˚

B. What angle does the incident ray make with the reflected ray? 106˚

What colors of light reflect off a mirror?

What colors of light reflect off a sheet of white paper?

Polarization of Light

Most light sources produce unpolarized, or incoherent light.

Polarization of Light

Most light sources produce unpolarized, or incoherent light.

A polarizing filter will cut out all light rays that don’t line up with

the filter’s orientation.

Polarization of Light

Most light sources produce unpolarized, or incoherent light.

A polarizing filter will cut out all light rays that don’t line up with

the filter’s orientation.

If a 2nd filter is added, that is parallel to the first, light still gets thru both.

Polarization of Light

Most light sources produce unpolarized, or incoherent light.

A polarizing filter will cut out all light rays that don’t line up with

the filter’s orientation.

If a 2nd filter is added, that is parallel to the first, light still gets thru both.

If a 2nd filter is added that is perpendicular to the 1st, no light gets thru both.

Polarization of Light

Most light sources produce unpolarized, or incoherent light.

A polarizing filter will cut out all light rays that don’t line up with

the filter’s orientation.

If a 2nd filter is added, that is parallel to the first, light still gets thru both.

If a 2nd filter is added that is perpendicular to the 1st, no light gets thru both.

Diffraction – bending of light around barriers

AM Radio Waves can bend over mountains

Diffraction – bending of light around barriers

Light waves can bend when passing thru small openings.

Double slit interference – proved light is a wave.

Diffraction – bending of light around barriers

Light waves can bend when passing thru small openings.

Double slit interference – proved light is a wave.

Less Bright

Dark

Bright

Dark

Brightest

Dark

Bright

Dark

Less Bright

Ch16 HW#2

Lab17.1 Reflection

- due tomorrow

- Ch16 HW#2 due at beginning of period

Ch16 HW#2

12. Light coming from the sun is coherent or incoherent?

What does this mean?

13. When 2 polarizing filters are placed so that they both are aligned

vertically, will light pass thru?

14. Polarizing filters are placed perpendicular to each other, will light

pass thru?

15. Incident ray strikes a plane mirror at 25˚ to the normal.

What is the angle of reflection?

Ch16 HW#2

12. Light coming from the sun is coherent or incoherent?

What does this mean?

Incoherent. It propagates outward as transverse waves in every

plane, and at many wavelengths.

13. When 2 polarizing filters are placed so that they both are aligned

vertically, will light pass thru?

14. Polarizing filters are placed perpendicular to each other, will light

pass thru?

15. Incident ray strikes a plane mirror at 25˚ to the normal.

What is the angle of reflection?

Ch16 HW#2

12. Light coming from the sun is coherent or incoherent?

What does this mean?

Incoherent. It propagates outward as transverse waves in every

plane, and at many wavelengths.

13. When 2 polarizing filters are placed so that they both are aligned

vertically, will light pass thru?

Yes

14. Polarizing filters are placed perpendicular to each other, will light

pass thru?

No

15. Incident ray strikes a plane mirror at 25˚ to the normal.

What is the angle of reflection?

Θi=25˚

Ch16 HW#2

12. Light coming from the sun is coherent or incoherent?

What does this mean?

Incoherent. It propagates outward as transverse waves in every

plane, and at many wavelengths.

13. When 2 polarizing filters are placed so that they both are aligned

vertically, will light pass thru?

Yes

14. Polarizing filters are placed perpendicular to each other, will light

pass thru?

No

15. Incident ray strikes a plane mirror at 25˚ to the normal.

What is the angle of reflection?

Θi=25˚Θr=25˚

Ch16 HW#2

16. An incident ray strikes a mirror at an angle of 50˚ to the mirror surface.

What is the angle of incidence and angle of reflection?

50˚

Ch16 HW#2

16. An incident ray strikes a mirror at an angle of 50˚ to the mirror surface.

What is the angle of incidence and angle of reflection?

40˚ 40˚

50˚

Ch17.2 – Refraction

Light bends as it passes from one medium to another.

- the more optically dense a material, the more it bends light.

- when passing from a less dense medium to a more dense medium

light bends towards the normal.

- when passing from a more dense to less dense medium

light bends away from normal

Index of refraction - a measure

(n = 1.0) of how much a material bends light.

Air ΘiFor this chapter:

Air: 1.0 water: 1.33 glass: 1.53

diamond: 2.42

(table pg397

Glass or internet)

(n = 1.53)

Air

(n = 1.0)

Ch17.2 – Refraction

Light bends as it passes from one medium to another.

- the more optically dense a material, the more it bends light.

- when passing from a less dense medium to a more dense medium

light bends towards the normal.

- when passing from a more dense to less dense medium

light bends away from normal

(n = 1.0)

Air ΘiΘreflection

Glass Θrefraction

(n = 1.53)

Θ

Air

(n = 1.0) Θ

Snell’s Law ni×sinΘi = nr×sinΘr

Ex1) A light ray passes thru air at an angle of 30˚ to an unknown transparent material at an angle of 19˚. What's the index of refraction ff the unknown material?

30

n = 1

nr = ?

19

Ex2) Light passes from air at an angle of 45˚ to diamond which has an index of refraction of 2.42. What angle does it pass thru the diamond at?

45

ni= 1

nr = 2.42

Θ

Snell’s Law ni×sinΘi = nr×sinΘr

Ex1) A light ray passes thru air at an angle of 30˚ to an unknown transparent material at an angle of 19˚. What's the index of refraction ff the unknown material?

AIR UNKNOWN

(1.0)×sin30 = nr×sin19

nr = 1.53

30

n = 1

nr = ?

19

Ex2) Light passes from air at an angle of 45˚ to diamond which has an index of refraction of 2.42. What angle does it pass thru the diamond at?

(1.0)×sin45˚ = (2.42)×sinΘr

Θr = 17˚

45

ni= 1

nr = 2.42

Θ

ni×sinΘi = nr×sinΘr

Ex3) A light ray passes from water (n = 1.33) at an angle of 40˚ into

glass (n = 1.53). What angle does it pass thru the glass?

40˚

ni = 1.33

nr = 1.53

Θ

ni×sinΘi = nr×sinΘr

Ex3) A light ray passes from water (n = 1.33) at an angle of 40˚ into

glass (n = 1.53). What angle does it pass thru the glass?

AIR UNKNOWN

(1.33)×sin40 = 1.53×sinΘ

nr = 34˚

40˚

ni = 1.33

nr = 1.53

Θ

Index and the Speed of Light

speed of light in a vacuum

(c = 3 x 108 m/s)

index of refraction

in that material speed of light in that

material

Ex4) Find the speed of light in water.

Index and the Speed of Light

speed of light in a vacuum

(c = 3 x 108 m/s)

index of refraction

in that material speed of light in that

material

Ex4) Find the speed of light in water.

Ch17 HW#1 1 – 6

Lab17.2 Refraction

- due tomorrow

- Ch17 HW#1 due at beginning of period

Ch17 HW#1 1 – 6

1. Light in air is incident on a piece of glass (n = 1.52) at an angle of 45˚.

Find the angle of refraction.

2. A ray of light passes from air into water (n = 1.33) at an angle of 30˚.

Find the angle of refraction.

45˚

ni = 1.0

nr = 1.52

Θ

30˚

ni = 1.0

nr = 1.33

Θ

Ch17 HW#1 1 – 6

1. Light in air is incident on a piece of glass (n = 1.52) at an angle of 45˚.

Find the angle of refraction.

2. A ray of light passes from air into water (n = 1.33) at an angle of 30˚.

Find the angle of refraction.

45˚

ni = 1.0

nr = 1.52

Θ

30˚

ni = 1.0

nr = 1.33

Θ

Find the angle of refraction. (Compare to #1)

4. A block of unknown material is submerged in water. Light in the water

is incident on the block at an angle of 31˚. The angle of refraction is 27˚.

Find the index of refraction of the block.

45˚

ni = 1.0

nr = 2.42

Θ

30˚

ni = 1.33

nr = ?

27˚

Find the angle of refraction. (Compare to #1)

4. A block of unknown material is submerged in water. Light in the water

is incident on the block at an angle of 31˚. The angle of refraction is 27˚.

Find the index of refraction of the block.

45˚

ni = 1.0

nr = 2.42

Θ

30˚

ni = 1.33

nr = ?

27˚

Find the angle of refraction. (Compare to #1)

4. A block of unknown material is submerged in water. Light in the water

is incident on the block at an angle of 31˚. The angle of refraction is 27˚.

Find the index of refraction of the block.

45˚

ni = 1.0

nr = 2.42

Θ

30˚

ni = 1.33

nr = ?

27˚

5. What is the speed of light in:

a. ethanol (n = 1.36)

b. quartz (n = 1.54)

6. What is the index of refraction of a plastic where the speed of light

is 2 x 108 m/s.

5. What is the speed of light in:

a. ethanol (n = 1.36)

b. quartz (n = 1.54)

6. What is the index of refraction of a plastic where the speed of light

is 2 x 108 m/s.

Ch17.3 – Applications of Light

Total Internal Reflection - Occurs when light passes from more dense

to a less dense medium. (Light rays bend away from normal)

Air, n = 1

Water,

n = 1.33

Critical Angle - angle where Θr = 90˚

Ex1) Find the critical angle for diamond into air.

Air, n = 1

Diamond,

n = 2.42

Ex2) Find the critical angle for glass into air.

Air, n = 1

Glass,

n = 2.42

Ex1) Find the critical angle for diamond into air.

Air, n = 1

Diamond,

n = 2.42

Ex2) Find the critical angle for glass into air.

Air, n = 1

Glass,

n = 1.52

Apparent Depth

Refraction makes objects appear closer than they actually are.

Blue skies and red sunsets

Refraction in the atm

bends and scatters

light. Higher freqs

scatter more.

Rainbows

Water droplets refract light like little prisms, reds bend less,

violets bend more, light colors meet at ur eyes from different drops.

Mirages

Hot temps refract light.

Ch17 HW#2

Lab17.3 – Total Internal Reflection

- due tomorrow

- Ch17 HW#2 due at beginning of period

Ch17 HW#2 7 – 14

7. Why are pages rough rather than smooth and glossy?

8. A light ray strikes a boundary between 2 transparent media.

What angle(s) is/are there no refraction?

9. Find unknown index

30˚

ni = 1.0

nr = ?

19.2˚

ni = 1.0

30˚

Ch17 HW#2 7 – 14

7. Why are pages rough rather than

smooth and glossy? Diffuses light

8. A light ray strikes a boundary between 2 transparent media.

What angle(s) is/are there no refraction?

9. Find unknown index

30˚

ni = 1.0

nr = ?

19.2˚

ni = 1.0

30˚

Ch17 HW#2 7 – 14

7. Why are pages rough rather than

smooth and glossy? Diffuses light

8. A light ray strikes a boundary between 2 transparent media.

What angle(s) is/are there no refraction?

Perpendicular

9. Find unknown index

30˚

ni = 1.0

nr = ?

19.2˚

ni = 1.0

30˚

Ch17 HW#2 7 – 14

7. Why are pages rough rather than

smooth and glossy? Diffuses light

8. A light ray strikes a boundary between 2 transparent media.

What angle(s) is/are there no refraction?

Perpendicular

9. Find unknown index

30˚

ni = 1.0

nr = ?

19.2˚

ni = 1.0

30˚

changes?

11. Light ray strikes a mirror at an angle of 53˚ to the normal.

a. What is the angle of reflection?

b. What is the angle between the incident and reflected rays?

changes?

As n gets bigger, v gets smaller

11. Light ray strikes a mirror at an angle of 53˚ to the normal.

a. What is the angle of reflection?

b. What is the angle between the incident and reflected rays?

changes?

As n gets bigger, v gets smaller

11. Light ray strikes a mirror at an angle of 53˚ to the normal.

a. What is the angle of reflection? 53˚

b. What is the angle between the incident and reflected rays?

106˚

12. Critical angle for glass.

13. Critical angle for diamond.

14. Speed of light in diamond.

Air, n = 1

Glass,

n = 2.42

Air, n = 1

Diamond,

n = 2.42

12. Critical angle for glass.

13. Critical angle for diamond.

14. Speed of light in diamond.

Air, n = 1

Glass,

n = 1.52

Air, n = 1

Diamond,

n = 2.42

12. Critical angle for glass.

13. Critical angle for diamond.

14. Speed of light in diamond.

Air, n = 1

Glass,

n = 2.42

Air, n = 1

Diamond,

n = 2.42

12. Critical angle for glass.

13. Critical angle for diamond.

14. Speed of light in diamond.

Air, n = 1

Glass,

n = 2.42

Air, n = 1

Diamond,

n = 2.42

Ch16,17 Review

1. Freq of a microwave with a wavelength of 3.0cm?

2. How many meters to a distant mountain if a light flash returns in 0.1s?

3. Red light + blue light =

4. Green plant absorbs _______ and reflects ________

5. Magenta paint and yellow paint are mixed, what color seen?

6. Red light and cyan light =

7. Red apple what color under: red light: _________

blue light: __________ magenta light: __________

8. Yellow banana what color under: white light: _________

yellow light: _________ red light: __________

blue light: _________ magenta light: __________

with the mirror. What is the angle of reflection?

10. A ray of light travels from air into a liquid, incident at 30˚

and refracted at 22˚. What is the index of refraction?

11. Light ray enters crown glass at 35˚. What angle does it pass thru?

What angle does it come out the other side?

n = 1.0

n = 1.53

n = 1.0