Topic 4: Lenses and Vision Topic 5: Extending Human Vision...

Light and Optics

Topic 4: Lenses and Vision

3. Investigate and explain the science of image formation and vision, and interpret relatedtechnologies

Topic 5: Extending Human Vision


Top7-TheW veMo4 Iofi.ight


Topic 8 - Beyond Light


How do lenses work?Lenses are used in cameras, telescopes, and other instruments

to refract and to focus rays of light. Lenses used as eyeglasses

help people with poor eyesight to see better.

Convex and concave lensesMost lenses are converging lenses. This means that light rays

passing through them are refracted and come closer together,

or converge. The lenses in some cameras, in some eyeglasses,

and in your eyes are converging ones. The simplest sort of

converging lens is thicker in the middle than at the edges.

Both surfaces of the lens curve down toward the edges. Lenses

like this are called convex. Converging lenses are used to

make things look bigger, or magnified.

Concave lenses are thicker at the edges than in the middle.

Their surfaces curve up toward the edges. They make light

rays spread out, or diverge. These lenses are often called

smaller. Astronomers use large telescopes with both convex

and concave lenses.

How do convex lenses refract light?You can see how convex lenses refract the light passing

through them by doing this experiment.

2. Poursome water and afew drops

of milk into the bottle or jar, and

place it about 6 inches (15cm) fromthe edge of a table. Switch on your

flashlight, and switch off the lights.

02iFind out more by looking at

pages 26—27

30—31

•1

ED

You will need:

a piece of cardboard, about

4inches(lOcm) x Binches(l5cm)

scissors

water and milk

modeling clay

a bright flashlight

a glass bottle or jar

1. Cut a pair of thin slits in the

cardboard. Each slit should be 2

inches (5cm) long. Leave 0.5 inch

(1 .25 cm) of space between slits.

Cl

33

Convex lensLook at an object, such asafly,

through a convex lens. The fly will

be magnified and appear bigger

than it really is.

Concave lensLook at a fly through a concave lens

and it will appear smallerthan it

really is.

convex lens

large image of a fly

concave lens

small image of a fly

3. Use the modeling clay to stick the

cardboard against the edge of the

table. Shine the flashlight through

the slits towards the bottle or jar. The

milky water makes the light rays

from the slits come closer together.

ocuses them like a converging

S.

Repeatthe experiment and aska

friend to hold the flashlight. Put your

eye where the two rays meet. What

do you see? Record your

observations in your notebook.

____

Tppjç 4: Lenses and VisionConcave lens•

_______

and

________

in the middlethan around theedges• light passing through , more curved areas willbend

________

than light passing throughareas•_light rays w or diverge after assIngthrough the lens

4.

:1

_______________

-

Convex lens

• thicker in the

________

than the

__________

• light rays will

________ __________

or converge afterpassing through the lens

Co rgr rays

A’.)

rfhg j- Cbj&t Light ryc

The amazing eye

The colored ring in your eye is aband of muscle called the iris.

Your eyes have a part called thelens, just like a camera. The lenshelps to bring everything you look atinto focus, so that details are asclear as possible.

The outer eye is covered by atransparent tissue called thecornea. The cornea focuses lightthrough the pupil.

The pupil looks like a black circle,but it is a hole in a ring of muscle.The pupil opens upto let in morelight at night and closes uponbright, sunny days.

Light travels through your pupil tothe retina at the back of your eye.The retina contains special cells,called rods and cones, whichrespond to light and color. Nervescarry messages from these cells toyour brain.

Your eyes are like two tiny movie cameras inside your head.They are sending a steady stream of pictures back to yourbrain, like a television camera sending live pictures back to aTV screen.

I

I \III

Changing shape

Rods and conesHuman beings are luckier than many other animals because

they see in color. Some other animals, such as birds and

butterflies, can also see colors.

To see colors, we have special cells in the eye called cones.

They share the work of seeing with other cells called rods.

Rods do not detect the difference between colors and don’t

need as much light as cones to make them work. So at times,

rods are more useful to you than cones, such as at night when

the light is very dim.

Have you ever been for a walk in the moonlight and noticed

how pale, silvery, and colorless everything seems?

Photographers can take pictures by moonlight which are just

as colorful as pictures taken by day. So the colors are still

there by moonlight, but we can’t see them. Can you think whynucleus

this is?

The cones help us to see color, but moonlight doesn’t

provide them with enough light to function well at night.

Muscles pull/on the lens to change its shape.

This allows you to look at something far awayand then to focus on an object close by. As youlook from the far-away object to the nearbyone, your lens changes shape. A sharp pictureof the object is focused onto the back of theinside of your eyeball. When you lookbackatthe far-away scene, the lens changes back toits original shape so quickly that you don’teven notice.

C

;_-

_& -,,—

The rods and cones in your retina

absorb the light which enters your

eye. They pass messages about the

flghtthrough nerves to your brain.

35

C)erve nerve

the lens isround and thick

light

the lens isflat and thin

far-away object

EyesThe human eye is a lens and focuses light on the

Problems with the eye:Near-sighted-trouble seeing objects, eyeball is toocorrected by

__________

lens

:0Myopia

zjQ

Myopia With Corredlon

Far-sighted-trouble seeing objects , eyeball is too

________

corrected by

__________

lens.

-,..,oeHyperopla With Corroction

Parts of the ye_: colored ring that control the opening of

the lens, pupil

_______________

natural adjustment in size of pupils

opening where light passes through to thelens

light rays bend as they pass through the lensfocusing the image

a1ightsensmveareaat the back of the eye

place where the retina is connected tonervous system; sends messages from the eye to the brain

protective outer covering of the eye

point where the optic nerve enters theretina and does not have any light-sensing cells

_____________

the shortest distance at which an object is in focus.

_____________

the longest distance at which an object is infocus, infinity.

Keeping it in Focus

-in order to keep objects in focus as they become closer to orfarther from the lens,

________________

to the

________

mustbe made.

-________

_________

change the shape of the lens so that0 things far away are in focus as well as objects that are close up

-accommodation:

N

With age the lens stiffens and loses its ability to change shapemaking it hard to focus on objects close up, resulting in readingglasses.

Different animals have their eyes in

differentpositions on their head.

Why do we have two eyes?Look at the pictures of the woodcock and the boy on thispage. What do you notice about the position of their eyes?

Why do you think the woodcock has its eyes on the sides of itshead? If you watch a woodcock feeding, you will see why.The woodcock has to keep a constant lookout for enemiessuch as foxes, so it needs to be able to see all around. In fact,many birds can see all around them, to help protect them fromdanger.

A woodcock has eyes atthe side of its head.

A human being has eyes atthe front of the head.

right visual field left visual field

IFind out more by looking at

pages 34—35

stereoscopic vision

©46 Animals and lightYour view of the world is very different fromthat of a cat, a dog, an owl, or an insect.Different species of animals have differentkinds of eyes to suit the way they live.

Night-huntersOwls hunt for food at night. They need tomake use of all the available light. They mustalso be able to judge distances accurately sothat they can swoop onto their prey. Owlshave huge eyes that face forwards.

Owls sometimes feed on rabbits. Rabbitshave eyes on the sides of their head for anall-around view. They need to keep alert forsigns of danger, such as a hunting owl.

The cat also has good nighttime vision.When a cat has just come in from the dark, itseyes look black. Its pupils are wide open tocatch every possible ray of light.

Fields of vision

When itis dark, the pupils in theowl’s eyes are very large, to let in asmuch llghtas possible.

When you look steadily at an object,everything that you see straight ahead of youand to the sides is in your field ofvision.Animals whose eyes are on the sides of theirhead, such as rabbits, have a large field ofvision. They can see almost all around them,which helps them to escape from predators.

Humans and some animals, such as owls,have a smaller field of vision because theireyes face forwards. Their field of vision hasan area of blindness called the blind spot.Animals with eyes at the sides of their headhave no blind spot.

owl

field of visionof right eye

blind spot

field of visionof left eye

47

rabbit

Compound eyesThe eyes of most insects are quite differentfrom ours. Each eye is made up of many tinylenses set at different angles. The eyes ofsome insects are made up of thousands ofthese lenses. This type of eye is called acompound eye. Although insects cannotmove or focus their eyes, some can see allaround them.

The bee also sees ultraviolet light, which isinvisible to our eyes. The petals of someflowers, particularly yellow ones, haveelaborate patterns which show up underultraviolet light. These patterns attract thebees to the flowers. Bees are unable to see thecolor red.

The bee notices moving objects

when light orshade moves across

differentparts ofits compound eyes.

human

Topic 4 Quiz

1. Complete the diagram to show what happens when light passesthrough

a. a concave lens b. a convex lens

fFtnthb1anks.

0a. When light rays pass through a concave lens they

When light rays pass through a convex lens they

b. If a person is near sighted, they cannot see

_____________

Their eyeball is

______________

than normal and will focus

objects

______________

the retina. This can be fixed using a

_______________

lens.

c. If a person is far sighted, they cannot see . Their

eyeball is

______________

than normal and will focus objects

_____________

the retina. This can be fixed by using a

_______________

lens.

d. In a

_______________

telescope, light from a distant object is

collected and focused by a

____________lens

called the objective

lens.

e. A

_______________

telescope uses a

____________mirror

called

the primary or objective mirror to collect rays of light from a

distant object.

f. Reflecting and refracting telescopes must have a large collector

(either a

__________

or a

__________)

in order to gather as much

light as possible from the distant object.

g. Binoculars are actually two

_______________

telescopes mounted

sidebystde;

3. The following is a list of parts of an eye. Give a description ofthe function of each.

a. retina

b. cornea

C. iris

d. pupil

e. optic nerve

4. Each of the following diagrams shows an eye which has visionissues. bescribe the problem, cause of the problem, and how tocorrect the problem.

HHEEEEEZE:E

5. The human eye and a camera have many similarities. Choose twoparts of a camera and compare them to the parts of the eye whichperform a similar function.

Topic 5: Extending Human Vision

There are a variety of tools which humans use to extendvision all based on understanding of light, mirrors andlenses

Telescopes -

Refracting telescopes- light from distant objects is

collected and focused by a

_______

lens (objective lens).

The eyepiece lens

_________

the image.

Reflecting telescope-

__________

mirror (objective mirror)

used to collect rays from distant object. The eyepiece lens

___________

the image.

1

4

\

________

rir

[ J(;

s of a Primary Focus Telescope

Looking through telescopesHave you ever looked through a telescope? It makes farawayobjects seem much nearer. You may even have your owntelescope. If so, it probably is a refracting telescope.

Retracting telescopesA refracting telescope has a piece of glass, called a lens, ateach end of a narrow tube. The large lens at the front of thetube bends, or refracts, the light that enters it. It produces animage at the other end that you can view through a secondlens, called the eyepiece.

Refracting telescopes are simple, but their strength is limitedby the size of the lens inside. The world’s largest refractingtelescope has a lens that measures about 40 inches (1 meter)across.

/

/F.,

•1

I

\

To make a huge mirror fora telescope, workersIUdU UIUUI (Ji yidb. IIILU d (fIWV IIIUIU. I IdIy,

rotating oven heats the mold, which melts the glassin the shape required fora telescope mirror.

1

I

Reflecting telescopesAstronomers normally use reflecting telescopes. These

contain curved mirrors as well as lenses. The mirrors are able

to collect more light than the lenses. This is important when

astronomers are looking at very distant stars and planets. The

world’s largest reflecting telescope has a curved mirror that

measures 20 feet (6 meters) across, It’s so good at gathering

light that you could use it to see a candle flame 15500 miles

(25,000 kilometers) away!

The mirror in a reflecting telescope is concave. This means

that its surface is shaped like the inside of a dish, When the

telescope is pointed at an object, light rays from the object are

ç)llected, or focused, by the mirror. The rays are then

reflected onto one or more other mirrors before being reflected

into the eyepiece, so that the image can be viewed,

Astronomers look at the stars with

this reflecting telescope. Before

they can do this, they have to open

partof the dome on top ofthe

building, so they can point the

telescope at the sky.

• ‘

• [

•.,• 3 • ••

What are the two main types of telescopes?

The two main types of telescopes are the refracting telescope and the reflectingtelescope. A refracting telescope uses only lenses, but a reflecting telescope uses acombination of lenses and mirrors.

Study the diagrams below. Look closely at the arrows that show the path of lightthrough each telescope and then answer the questions on the next page.

Refracting Telescope

Reflecting Telescope

Copyright © Re:ource Development Services, Edmonton Public Schools, 2004.

0

light fromdistantobject

1\

light fromdistantobject

Grade 8 Light and Optical Systems

22

Write the word refracting or reflecting in the blanks in each of the followingsentences to make them correct.

1. Arefof light.

— —— ting telescope uses a concave, circular mirror that collects rays

2. A ref — — — ting telescope has two lenses—one on each end of a longtube.

3. In a ref — — — ting telescope, light only moves in one direction.

4. In a ref — — — ting telescope, light moves in three different directions.

5. In a ref — — — ting telescope, a large lens catches the incoming light andbrings the light’s rays close together and focuses them on the lens in theeyepiece.

6. In a ref — — — ting telescope, a large mirror reflects the incoming light to amirror under the lens in the eyepiece that brings the light rays close togetherand focuses them.

Did you know?The Hubble Space Telescope is a moving observatory in outer space that was built forbenefit of the international astronomical community by the European Space Agency(ESA) and the National Aeronautics and Space Administration (NASA).

Grade 8 Light and Optical Systems

secondary mirror

light shield

mirror

Copyright © Resource Development Services, Edmonton Public Schools, 2004.

23

Binoculars

- Binoculars are made up of two

__________

telescopes- The telescopes are shortened by placinginside which act as a

__________

mirror.- Light is reflected and refracted in the short tube.

Porro-Prism Binocularsrain QCUS

(tharnbsoew)

Lht Path

Microscopes. Telescopes. and Scientific Knowledge- A compound microscope has an objective lens that forms areal image of the object that can be focused using theeyepiece

• /

objactivo

How do cameras work?Cameras can be very expensive to buy or theycan be very cheap. You can even buy a camerathat you throw away when you have used upthe film! But all cameras have the same mainparts. This drawing shows the importantparts of a camera. You can find out how eachpart helps in taking a photograph.

The film inside the camera is

sensitive to light. It is coated with

chemicals that change when lighti shines on them. These chemicals

change more quickly on some films

than on others.If you are taking photographs on a

cloudy day or indoors, you use a“fast”film, which isverysensitivetoNht.OnahtnnYoseJ

-

The inside lining of the cameracase is colored black so that nounwanted light reaches the film.

The shutter is like a small gate thatopens to let in the light and thencloses again. Adjustable shutterspeed allows the gate to remainopen for different lengths of time.

IThe viewfinder shows you thepicture you are about to take withthe camera. Some viewfinders allowyoutolookthroughthem andthecamera lens at the same time.Many viewfinders have a mechanismto let you know if there is enoughlight to take a picture.

/.,

0

_:

The focus setting is turned to alter

the position of the lens until the

object is in focus. Some cameras

focus on an object automatically.

I

35

LFind out more by looking at

pages 26—27

I

The lens refracts light that comes

from an object and focuses it as a

sharp image on the film. With some

cameras, the lens can be adjusted

focus on objects at different

distances.

The aperture is the opening that is

made when the shutter opens. The

aperture control adjusts the size of

the opening to allow different

amounts of light into the camera.

Part K: How are our eyes like film cameras?

ciliarymuscle

retina

The iris is the coloured part of the eye. The black part in the middle is the pupil. Thepupil is an opening controlled by a circle of muscles that open and close to adjustthe amount of light passing into the eye. When the light goes into the eye, it passesthrough a convex lens that brings the light rays together and focuses them. Thefocused light hits the retina at the back of the eye. The retina is like a movie screenthat is attached to the brain by the optic nerve. The image that is projected ontothe retina is actually an upside-down version of what the eye is looking at. The brainis-able-to-figure-outthat the image is upside down.

lens

The lens of a camera is on the front. Light shines through the convex lens that bringsthe rays together. The light then passes through the hole in the diaphragm(di-a-fram) that opens and closes to let light in. The image is projected onto thecamera film. The image is upside-down but, with photographs, at! the developerneeds to do is flip it the other way to see it properly!

Did you know?

Different kinds of optical technology use lenses in a way that flips images upside down. You can Acheck this by drawing the letter “e” on a piece of paper and looking at it under a microscope.

Copyright © Resource Development Services, Edmonton Public Schools, 2004. Grade 8• Light and Optical Systems

iris

cornea

lens

opticnerve

shutter

27

Use what you have learned to answer these questions.

1. Match the parts of the eye with their partner” part of a film camera.

a. pupil

___developer

b. lens

____

film

c. retina

___

diaphragm

d. brain

____

lens

2. Complete this Venn diagram to compare our eyes to a film camera.

-,-a a —

-, , .—4

4 -, Ot

‘. —,

(4

S

‘aa,

I

__

r I II II I II I II I II I

SS

3. When a person has to wear glasses, what part of their eyes is probably notworking properly? Why do you think so?

.Copyright © Resource Development Services, Edmonton Public Schools, 2004. Grade 8 Tight and Optical Systems

28

New biscoveriesScientist are able to further their understanding of cancer,genetics and cellular activities because of our increasedability to see and study microscopic activities, based on ourknowledge of light, mirrors and lenses.

Question - How would life be differentwithout the discovery of one of the previousdevices used to extend human vision?

Topic 7 - The Wave Model of Light

Looking at Wavelength

Wavelength Terminologytrow4icrest

I — wavelength

0The high parts of the wave are called

______________

The low parts of the wave are called

_______________

The distance from crest to crest is called

_____________

(the distancefrom one complete crest and one complete trough).

The height of the crest or the depth of the trough from rest position iscalled the

_______________

The

________________

is the rate at which the crest and the troughmove up and down.

The number of cycles in a period of time - which is usually measured in

__________

or cycles per second.

The Wave Model of Light

The wave model of light pictures

______

traveling as a wave. Itdoesn’texplain everything about how light

________

but it helps us visualize it.

behavior, like when light curves around a opening.

When light passes through a small opening, the waves

________________•

If the wavelength is

________,

the waves spread out

__________

whereas

_______

wavelengths spread out

________

Light Waves in Action

Sunsets can be explained using the wave model of light. As lightwaves from the sun travel through Earth’s atmosphere, they strikeparticles of different sizes, including dust and other elements.

1’

The longer wavelengths of the reds and oranges tend to pass aroundthese particles, whereas, the shorter wavelengths of blue and violet,strike the particles and reflect and scatter. At sunset, the light we seepasses through about 700 kms of the Earth’s atmosphere. There aremany more particles in the atmosphere at this time of the day, due tothe activity going on during the day - so many more blue and violetwaves are reflected away. Red and orange are the vibrant colors wesee at sunset.

Making a Sunset - Page 245

Laser Light

In 1966, Theodore H. Maiman, a physicist at Hughes AircraftCompany in California became the first person to use aprocess called...

Tightamplification by thestimulatedemission ofradiation

or

________

light

Incandescent lights give off many different colors andtherefore have many different

_________

and

The waves are

__________

and crestsfrom one wavelength might overlap thetrough of another, making the waveswork against each other. This type oflight is

__________

Laser light is quite different. It gives off a(frequency) of

______________

light.wavelength

f

C

Lasers have many useful applications:

• Scanners (bar codes in retail shops are scanned to give theprice)• Digitized data are read by a laser on a compact disk (CD)• Lasers are use by law enforcement officers to detect thespeed of vehicles.

beam. In either form, it is so powerful, that it can make preciseQ cuts through metal and can also be used in surgery, as a Q

scalpel - or, to instantly seal broken blood vessels, because itproduces such intense heat.• Eye surgeons use lasers to correct vision defects (shaving offareas of the cornea - to correct problems caused byirregularities in the shape of the eyeball)• They can also ‘spot weld’ a detached retina• One day dentists may use lasers to vaporize cavities, insteadof drilling into them.

0

DATE: NAME: CLASS:

FOPIC 7BLM 3-23

SKILL BUILDER i Riding the Waves

Goal • Review wave concepts.

What To DoAnswer each question in the space provided. Refer to pages 238 and 239 of your textbook if youneed to review.

1. (a) Label the diagram below using the following terms: trough, amplitude, crest,wavelength, rest position.

2. The number of cycles per second is the

___________________.

This is measured in

_______(Hz).

3. Calculate the frequency of a wave that goes up and down 8 times in 4 s.

_______________

4. (a) Examine the diagram below. How many wavelengths apart are the two ducks?

starts here• ends here

(b) How many wavelengths are shown in the diagram?

0

Copyright © 2001, McGrawHil1 Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved.1 92 This page may be reproduced for classroom use by the purchaser of this hook without the written permission of the publisher.

Topic 8 - Beyond Light

The sun emits both visible and invisible energy. The light wesee is the visible energy the sun emits. All forms of radiantenergy, including light energy, exist on the electromagneticspectrum.

decreasing wavelength

increasing frequency

V

infrared I I

g

AM radio te[svisionchannels

shortwave FM radarradio radio

microwave:radio waves

F

ultraviolet X rays gamma rays

Fiqure 3.62 The 9: Etr. etL. CtrLI

Electromagnetic Spectrum - Invisible Energy

Where does itotherfall on the

interestingWhat is it? Where is it used?electromagnetic

things?spectrum?

InfraredRadiation

Radio Waves

UltravioletRadiation

X rays

Gamma Rays

Topic 4: Lenses and Vision Topic 5: Extending Human Vision...

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