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PHY205H1F Summer

Physics of Everyday Life

Class 10: Colour, Optics

• Color in Our World

• Mixing Colored

Light

• Why the Sky Is

Blue

• Why Sunsets Are

Red

• Law of Reflection

• Virtual Image Formation

• Image Reversal

• Concave Mirrors

• Diffuse Reflection

• Refraction

• Total Internal Reflection

• Lenses

Recall from Chapters 25 and 26…

A changing electric field creates a field, which then changes in just the right way to recreate the field, which then changes in just the right way to again recreate the field, and so on.

This is an electromagnetic wave.

E

M

What property of a light wave mainly

determines its colour?

A. Its frequency

B. Its amplitude

C. Its timbre

D. A mix of all of the above

Why Sunsets Are Red

CHECK YOUR NEIGHBOR

Color we see depends on frequency of light.

High Frequency,

Short

Low Frequency,

Long

𝑓

𝜆

Color

0.4 𝜇m 0.7 𝜇m

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Selective Reflection

A red ball seen

under white light.

Only is

reflected, other

colors are absorbed.

A red ball seen

under red light.

A red ball seen

under green

light.

There is no

source of red

light to reflect!

Mixing Colored Light

The spectrum of sunlight is a graph of

brightness versus frequency.

A beam of white light, when shone through a

prism, will end up many different colours.

What will happen if a green laser is shone

through a prism?

A. It will spread into a small range of

colours.

B. It will change to a single colour other

than green.

C. It will stay green.

Why Sunsets Are Red

CHECK YOUR NEIGHBOR Rods and cones contain stacks of membranes. Rhodopsin is a transmembrane protein complex.

Cone Rod

Light Light

Rhodopsin

Retinal

(pigment)

Opsin

(protein

component)

The retinal molecule inside rhodopsin changes shape when retinal absorbs light.

Light

trans conformation

(activated)

Opsin

cis conformation

(inactive)

0.5 µm

Opsin

Slide courtesy of Ross Koning, Biology Department, Eastern Connecticut State University

http://plantphys.info/sciencematters/vision.ppt

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Slide from http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colcon.html

Response Curves for the three types of cones in

the retina of the human eye.

Use both eyes, stare at area shown in blue for 15 seconds or so

What do you see on this blank white slide? Blink if needed!

This is called an “after image”

Does it move around as you move your gaze?

Use both eyes, stare at the parrot’s eye for 15 seconds or so Stare at the bird’s eye for 10 seconds without tilting your head.

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What colour is

the afterimage

bird?

A. orange

B. green

C. blue

D. yellow

E. None of

the above

Bird Was Red Use both eyes, stare at the parrot’s eye for 15 seconds or so Stare at the bird’s eye for 10 seconds without tilting your head.

What colour is

the afterimage

bird?

A. red

B. orange

C. blue

D. violet

E. None of

the above

Bird Was Green Use both eyes, stare at the parrot’s eye for 20 seconds or so Stare at the bird’s eye for 10 seconds without tilting your head.

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What colour is

the afterimage

bird?

A. red

B. orange

C. yellow

D. green

E. None of

the above

Bird Was Blue

Additive Primary Colours (light bulbs)

and Subtractive Primary Colours (ink)

Discussion Question

• Why is this square red?

A. The light bulbs in the projector emit light with

blue frequencies

B. The light bulbs in the projector emit light with

green frequencies

C. The light bulbs in the projector emit light with

red frequencies

D. Both A and B

Discussion Question

• Why is the red folder in Harlow’s hand

red?

A. The pigments in the paper absorb light

with blue frequencies

B. The pigments in the paper absorb light

with green frequencies

C. The pigments in the paper absorb light

with red frequencies

D. Both A and B

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• When the colour yellow is seen on the

screen of your computer, what are the

lights being activated in that region of your

screen?

A. Mainly yellow

B. Blue and red

C. Green and yellow

D. Red and green

Discussion Question : Using the

colour wheel..

• If an object is blue, which of the coloured

lights below would make the object appear

most black?

A. blue

B. cyan

C. yellow

D. magenta

Discussion Question : Using the

colour wheel..

• If an object is red, which of the coloured

lights below would make the object appear

not appear red?

A. red

B. orange

C. white

D. cyan

Discussion Question : Using the

colour wheel..

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Why the Sky Is Blue For small scattering particles, like nitrogen or oxygen molecules, frequency blue light is scattered much more readily than lower frequency red light.

Why the Sky Is Blue

𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦

If molecules in the sky scattered orange light

instead of blue light, the sky would be

A. orange.

B. yellow.

C. green.

D. blue.

Why Sunsets Are Red

CHECK YOUR NEIGHBOUR Doppler Shift for Light

• When a light source is moving from

you, the spectrum is shifted toward the red.

• When a light source is moving you,

the spectrum is shifted toward the blue.

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Doppler Shift for Light

• The Doppler shift can be observed with carefully obtained spectra of very fast moving objects like stars

• There is a slight shift in “absorption lines”

Why Sunsets Are Red

Light that is least scattered is light of low

frequencies, which best travel straight through air.

If molecules in the sky scattered orange light

instead of blue light, sunsets would be

A. orange.

B. yellow.

C. green.

D. blue.

Why Sunsets Are Red

CHECK YOUR NEIGHBOUR

Why Clouds Are White

• Clouds are clusters of various sizes of water droplets

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Why Clouds Are White

Size of clusters determines scattered

cloud color.

• Tiny clusters produce bluish clouds.

• Slightly large clusters produce greenish clouds.

• Larger clusters produce reddish clouds.

• Overall result is white clouds.

• Slightly larger clusters produce a deep gray.

• Still larger clusters produce raindrops.

What does a white sky indicate?

A. The atmosphere has mostly particles smaller

than the wavelength of light

B. The atmosphere has mostly particles larger

than the wavelength of light

C. The atmosphere has a mixture of particle sizes

D. The atmosphere has a lot of water vapour

E. The atmosphere is filled with pollutants.

Why Sunsets Are Red

CHECK YOUR NEIGHBOR

Law of Reflection The angle of reflection equals the angle of incidence.

© 2010 Pearson Education, Inc.

Mirror

• A dentist uses a mirror to

look at the back of a

second molar (A).

• Next, she wishes to look

at the back of a lateral

incisor (B), which is 90°

away.

• By what angle should she

rotate her mirror?

A. 90°

B. 45°

C. 180°

A

B

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Virtual Image Formation

No light rays actually pass through or even near the image, so it is “virtual”.

Two plane mirrors form a right angle.

How many images of the ball can the

observer see in the mirrors?

A. 1

B. 2

C. 3

D. 4

• Which picture is most likely a mirror image of

Harlow? • Alice looks at Bob’s image a mirror and sees he has a

red shoe on the foot to Alice’s left.

• Then she asks Bob to turn and face her, so she can

compare the image to what Bob looks like in real life.

• Bob takes a couple of steps forward, turns around and

faces Alice.

Virtual Image Formation

• Alice notes that the red shoe is now

on the foot on the .

• Alice concludes: “Mirrors reverse left

and right, not up and down.” Is this

true? Can you see any flaws in

Alice’s reasoning?

mirror real

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Bob in Mirror

Bob turns to

face Alice

• Bob chooses to rotate around a vertical axis,

and therefore he looks flipped left-to-right.

• But if Bob wants to turn to face Alice, is there

any other way to do it?

Virtual Image Formation • What really happens is the image is reversed

front-to-back

Refraction

When light bends in going obliquely from

one medium to another, we call this process

refraction.

Cause of Refraction • Bending of light when it passes from one medium

to another

• Caused by change in of light

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Dry Land

Mud

Dry Land

1

2

A soldier wants to get from point 1 to

Point 2 in the shortest amount of time.

Marching through mud is much

slower than marching on dry land.

Which might be the best path?

A B C

Refraction

Light travels in glass than in air, so it

minimizes the time it spends in the glass.

© 2010 Pearson Education, Inc.

A fish swims below the surface of the water.

An observer sees the fish at:

A. a greater depth than it really is.

B. its true depth.

C. a smaller depth than it really is.

air

water

Dispersion

• Process of separation of light into colors arranged by frequency

• Components of white light are dispersed in a prism (and

in a diffraction grating).

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Rainbows

Rainbows are a result of dispersion by many drops.

• Dispersion of light by a single drop

Rainbows

Antisun

Radius of circle is about 41°

Double-

rainbow

The second rainbow

has blue on the top,

and a radius of about

53°

Total Internal Reflection

• Total reflection of light traveling within a medium that strikes the boundary of another medium at an angle at, or greater than, the angle

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Discussion Question

• Light waves with speed v1 are incident upon the flat

surface of a material in which they have speed v2.

• For what condition is total internal reflection possible?

A. v2 > v1

B. v2 < v1

C. v2 = v1

D. All of the above

An Optical Fibre

Speed of light in cladding is than

speed of light in core.

Medical Fibrescopes

Video-

laryngoscopy

with a flexible

fiberscope

Converging Lens

Focal Point

, f

NOTE: Focal length is defined

for initially parallel rays.

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Diverging Lens

Virtual Focal

Point

Negative

, -f

Rays appear to emerge

from Virtual Focal Point

Diverging rays through a Converging Lens

, f

If an object emits rays at the focal point, they

end up being parallel on the other side of the

converging lens.

What will happen to the rays emerging to the

right of the lens if the face is moved a little

further away from the lens?

A. They will remain parallel.

B. They will diverge (spread out).

C.They will converge (toward a focus).

f Real Image Formation

, f

Light rays actually pass through the image, and a screen can be placed there, so it is “real”.

image

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The Camera

• A camera “takes a picture” by

using a lens to form a real, inverted

image on a light-sensitive detector

in a light-tight box.

• We can model a combination lens

as a single lens with an

focal length (usually called

simply “the focal length”)

• A zoom lens changes the effective

focal length by varying the spacing

between the converging lens and

the diverging lens.

This is the end!!!!

The final exam, will be:

Wed. June 26 at 1:00pm sharp! (not 1:10!)

Rooms TBA

Test will begin promptly at 1:00 and will be 2 hours

long.

Please bring a calculator, and, if you wish, a letter-

sized aid sheet upon which you may write anything

you wish

This is the end!!!!

The final exam will cover the entire course, including all of the assigned reading plus tutorial materials and what was discussed in class.

Approximately even spread over the course material

Final Exam: First Page

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