M2 ScienceEye and Optics

Enduring Understandings

Science

ESOL

· A medium can refract light.

· Shape determines how lenses form images.

· The eye is a natural optical tool.

· Corrective lenses can improve vision.

Essential Questions

Science

ESOL

· What happens when light strikes an object?

· Why do light rays bend when they enter a medium at an angle?

· What determines the type of images formed by convex and concave lenses?

· How do humans see objects?

· What are the types of lenses used to correct vision problems?

Content

Science

ESOL

· See below

Indicators

Science

ESOL

Students should be able to:

· Trace the path of light as it travels through different shaped lenses

· Describe how lenses produce images

· Understand how the eye forms images

· Identify the lens shapes that correct vision

· Identify parts of the cow/sheep eye and describe functions

· Compare and contrast pinhole camera and human eye

How Light Travels

Light is a form of energy. It travels:

· In waves,

· Through empty space

· Very quickly (186,225 miles per second)

· In straight lines called rays.

What Happens When Light Hits an Object?

A. Reflection

When light rays hit a smooth, shiny surface such as a mirror, they bounce back. You see whatever is in front of the surface. This is called reflection.

B. Refraction

Light rays cannot turn corners. But, they can be bent by things in their path. When a light ray goes through a different substance, such as glass or water, it changes direction. Then they ray comes out on the other side and goes straight on. This is called refraction

Summary

When a ray of light hits a shiny surface it is REFLECTED.

When light passes from one transparent material to another it is REFRACTED (bent).

What do Lenses Do?

· Bend light for other uses. Most lenses are made out of glass

· Examples: camera lenses take pictures, eyeglasses help people to see, contact lenses help people to see, microscope lenses help people see really small things

Types of Lenses:

A. Convex: this makes the light focus to a point

B. Concave: this make the light spread out, like a flood light

The Eye: How Do Your Eyes Turn Light Into What You See?

Your eyeballs are almost round. They have a thin covering called the cornea. The cornea helps to protect your eyes. The black circle in the middle of each of your eyes is the pupil. The pupil is a hole. Light goes through the pupil

The colored part of your eye around the pupil is the iris. The iris changes the size of the pupil to let in the right amount of light. When the light is bright, the iris makes the pupil small. When the light is dim, it makes the pupil large.

Light enters the pupil and goes through the lens. The lens bends light rays so they hit the retina at the back of the eye. The retina is attached to the optic nerve. The optic nerve sends messages to your brain. Your brain sees these messages as pictures.

Label the Eye. Use the words in the vocabulary box.

corneairislensoptic nerve

pupilretinavitreous

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How Do Lenses Correct Eyesight/Vision?

This is an “eye chart.” If you have 20/20 vision, it means that at a distance of 20 feet, you can read a certain line on the chart and your vision is normal. (This line is labeled ‘line 20.’) If you can only see the top line, then your vision is 20/200. That top line is labeled ‘200.’ This means that you can see at 20 feet, what most people can see from 200 feet.

What happens if your vision is not “perfect?” Vision depends on the shape of your eyeballs. The shape of your eyeballs determines where the light rays land. If your vision is not perfect, you will need to get glasses. Let’s look at two types of imperfect vision:

I. Fuzzy – Myopic – Nearsighted Vision

If you have difficulties see things far away from you, then your are myopic, or nearsighted. The light enters your eye, BUT doesn’t reach the retina. You have a slightly longer eyeball. People need a concave lens to “fix” this. (Remember that this makes the light spread out more.) The light will now reach the retina.

II. Fuzzy – Hyperopic – Farsighted Vision

If you have difficulties seeing things close to you, e.g. when reading books, cereal boxes, etc. then you are hyperopic, or farsighted. The light enters your eye, AND goes behind the retina. You have a slightly shorter eyeball. People need a convex lens to fix this. (Remember that this makes the light focus into a point.) The light now reachs just the front of the retina.

The Eye and What Type of Lenses are Needed to Correct Its Vision

Determine if the Eyeball is “Normal,” Myopic, or Hyperopic. Explain why.

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Lenses

You know that light can be refracted or bent. Lenses are used for bending light. They can make objects look small or larger. They can make things that are far away look close. How do lenses work?

Lenses are made of glass or other materials that light can pass through. The two main kinds of lenses are concave lenses and convex lenses. A concave lens is thinner in the middle than it is at the edges. A concave lends bends light rays so that they spread apart. A convex lens is thicker in the middle than it is at the edges. A convex lens bends light rays so that they come together.

Compare concave and convex lenses. Put this information in a chart.

Concave Lenses

Convex Lenses

Lenses have many different uses. People who have trouble seeing wear eyeglasses or contact lenses. Eyeglasses are lenses worn in front of the eyes. Contact lenses are lenses worn on the eye. Contact lenses are made of plastic. Concave lenses help people who have trouble seeing objects in the distance. Convex lenses help people who have trouble seeing objects close to them.

Scientists use lenses in microscopes. The lenses in microscopes make very tiny objects look larger. Scientists use microscopes to study things that are normally too small to see. Scientists also use lenses in telescopes. Telescopes make faraway objects look as if they are closer. Scientists use telescopes to study stars and planets.

Lenses are used in cameras. They focus light on the film. Without lenses, there would not be photographs or movies.

Turn the following into questions. The question must be one that would give an answer like the ones below.

1. Our eyes have over 2,000,000 working parts!

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2. A blink of an eye takes 1/10 of a second.

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3. An average person blinks approximately 17,000 times per day.

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Our eyelashes help keep airborne particles and sweat from entering our eyes.

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An adult’s eyeball is actually the approximate size of a golf ball!

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Match the vocabulary with the definition

Cornea

The colored part of the eye that is a ring of muscles that control how much light is passed in to the eye. It contracts to limit light intake and expands to allow more light intake. A pigment called melanin gives it its color

iris

The white protective area that covers most of the eye

lens

A light-sensitive membrane that lines the inner eyeball and is connected to the brain via the optic nerve

pupil

A thin covering that protects the eye

retina

Lies just behind the pupil and is the area that focuses light that enters the eye

sclera

The opening in the center of the iris, which protects the inside of the eye. It changes depending on the amount of light. In low light, it relaxes allowing more light. In bright light the muscles contract to allow less light

Iris –

Pupil – the opening in the center of the iris that changes depending on the amount of light to protect the inside of the eye. In low light the pupil relaxes allowing more light. In bright light the muscles contract to allow less light

Lens –Retina –

Normal eyesight is present when light rays strike the retina, causing a clear image to form

In myopia (nearsightedness), rays of light focus in front of the retina instead of upon it, causing distant objects to appear blurred www.wangvisioninstitute.com/book/chap-02.html

In hyperopia (farsightedness), rays of light focus behind the retina.

A camera has a convex lens. It focuses light on an electronic imaging sensor or a photographic film.

The image on the sensor or film is upside down. The camera turns the image the right way up on the viewing screen or in the viewfinder.

Lenses are used to correct eyesight when, because of the shape of the eye, the light doesn't focus exactly on the retina.

People who are near sighted have a slightly longer eyeball, so the light focuses just in front of the retina. A concave lens makes the light focus further back so it focuses exactly on the retina and the person sees a sharp image.

People who are far sighted have a slightly shorter eyeball, so the light focuses just behind the retina. A convex lens make the light focus further forwards so it focuses exactly on the retina and the person sees a sharp image.

Fiber optics involves sending light down thin transparent flexible plastic or glass fibers. A fiber optics cable consists of many separate fibers.

Light travels in straight lines inside an optical fiber by reflecting off the internal walls of the fiber.

Telephone messages can be carried by light in a fiber optics cable. Digital messages consist of ones (light on) and zeros (light off). Special electronic devices turn the sequence of ones and zeros into sound. CD players also work by turning light, reflected from the surface of the CD as a sequence of ones and zeros, into sound.

Pictures: www.hobbyprojects.com/general_theory/light.html

· Light is given off in tiny particles called photons. Photons have no mass. They are not matter. Photons travel in waves. Most light waves have so many photons that the separate photons cannot be seen. They look like solid waves of light.

Sound waves of movements of the matter through which they travel. So, wound waves can travel only through matter. But light waves are waves of photons. So light waves can travel through empty space.

Light travels very quickly. It goes through 186,225 miles ( kilometers) of air in 1 second. Light travels much faster than sound. Sound goes only about one fifth of a mile in a second. If you have been in a thunderstorm, you probably saw the lightning before you heard the thunder. The light from the lightning reached you more quickly than the sound did.

Light travels in straight lines called rays.

Long sight. The eye really is too short; the light rays do not meet before striking the retina

The rays of light (A) enter the eye, and are focussed on the retina by the lens

Short sight. In this case the eye is too long from front to back, or the lens is too curved ways read in sufficient light so that it falls upon the work from above and behind. The eyes should never be used at twilight. Flickering gas-jets and lamps are extremely injurious to the eyes. If the eyes are tro uble-some, it is best to use them only in daylight.

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· Explain that our eye is much more complex then the visual part, or front, of our eye that we see when we look in a mirror.

· Explain to students the various parts of the eye, using worksheet 1a:

· Iris – the colored part of the eye that is a ring of muscles that control how much light is passed in to the eye. It contracts to limit light intake and expands to allow more light intake. A pigment called melanin gives the iris its color

· Pupil – the opening in the center of the iris that changes depending on the amount of light to protect the inside of the eye. In low light the pupil relaxes allowing more light. In bright light the muscles contract to allow less light

· Lens – lies just behind the pupil and is the area that focuses light that enters the eye

· Sclera – the white protective area that covers most of the eye

· Retina – a light-sensitive membrane that lines the inner eyeball and is connected to the brain via the optic nerve

· Explain how the eye works:

· Light passes through the cornea and the pupil and is then focused by the lens into the vitreous humor and is projected onto the retina. The retina is like the film in a camera that captures the images.

· Light sensitive receptor cells convert the light into messages that are sent to the brain via the optic nerve.

· The eye is similar to the camera in how it works. With our eyes, light passes through the lens and cornea and bends or refracts. When it refracts the image turns upside down and backward onto the retina. With a camera light enters the lens and turns upside down and backward onto the film.

Definitions of Parts of the eye

Cornea - the clear, dome-shaped tissue covering the front of the eye. Iris - the colored part of the eye - it controls the amount of light that enters the eye by changing the size of the pupil Lens - a crystalline structure located just behind the iris - it focuses light onto the retina Optic nerve - the nerve that transmits electrical impulses from the retina to the brain

Pupil - the opening in the center of the iris- it changes size as the amount of light changes (the more light, the smaller the hole) Retina - sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve Vitreous - a thick, transparent liquid that fills the center of the eye - it is mostly water and gives the eye its form and shape (also called the vitreous humor)

Content From Science Curriculum

Part A

When light passes at an angle from one medium (e.g. air) into a different medium (e.g. water or glass) it is bent. This is why people's legs look shorter when they are standing in a swimming pool.

Lenses are designed to bend light in useful ways. Most lenses are made of glass.

A convex lens focuses light to a point. A concave lens makes the light spread out.

A camera has a convex lens. It focuses light on an electronic imaging sensor or a photographic film.

The image on the sensor or film is upside down. The camera turns the image the right way up on the viewing screen or in the viewfinder.

Lenses are used to correct eyesight when, because of the shape of the eye, the light doesn't focus exactly on the retina.

People who are near sighted have a slightly longer eyeball, so the light focuses just in front of the retina. A concave lens makes the light focus further back so it focuses exactly on the retina and the person sees a sharp image.

People who are far sighted have a slightly shorter eyeball, so the light focuses just behind the retina. A convex lens make the light focus further forwards so it focuses exactly on the retina and the person sees a sharp image.

Fiber optics involves sending light down thin transparent flexible plastic or glass fibers. A fiber optics cable consists of many separate fibers.

Light travels in straight lines inside an optical fiber by reflecting off the internal walls of the fiber.

Telephone messages can be carried by light in a fiber optics cable. Digital messages consist of ones (light on) and zeros (light off). Special electronic devices turn the sequence of ones and zeros into sound. CD players also work by turning light, reflected from the surface of the CD as a sequence of ones and zeros, into sound.

Part B - The Eye

The parts of the eye are cornea, sclera, pupil, iris, lens, retina and optic nerve.

The cornea is the transparent front surface of the eye.

The sclera is the white of the eye.

The pupil is the hole in the iris through which light passes on its way to the retina.

The iris can change the size of the pupil. It regulates the amount of light entering the eye.

The lens focuses light on the retina.

The lens is convex. It can change shape so you can focus light onto the retina from objects at different distances.

The retina senses the light.

The image on the retina is upside down.

The optic nerve is a bundle of neurons that carry messages from the retina to the brain.

The brain turns the image the right way up.

ELL – March 2010Page 3