Download Science 8Optics and Vision

Science 8 – Optics and Vision
In this unit we will study light and all of its properties to help explain how we see, how colours form and
how lenses and mirrors work. During the study of this unit, you will need to bring a ruler, protractor,
pencil, and a light source to class for the labs and demonstrations.
Lesson 1 – What is Light?
These notes are taken and adapted from: http://www.edquest.ca/component/content/article/184/
Simply stated, light is the form of energy you can see. This energy can be produced naturally by the sun or fire,
or artificially by light-producing technologies, like batteries. Radiation is the wave like transfer of light from its
source in all directions. Light is often called radiant energy.
Light is a form of energy that can be absorbed and transformed into other types of energy.
? into electrical energy
? into thermal energy
? into chemical energy
Solar cells change light into
Cameras change light into
Trees convert light energy into
electricity
thermal images
food (chemical energy)
The amount of energy a surface receives depends on the intensity of the light.
The more intense the light, the more light can be absorbed.
Sources of Light
Natural Light Sources
Sun
Artificial Light Sources
Incandescent
(heat causing a filament of metal
to glow - visible light)
Electrical energy ---? Thermal
energy ---? Visible light energy
Candles or Oil
Lamps
Florescent
(ultraviolet light is absorbed by
fabric particles, which in turn
emit some of the energy as light glowing)
Ultraviolet light ---? Energy
absorbed ---? Visible light
energy by particles energy
Wood (fire)
Phosphorescent
(light energy is stored and
released later as visible
light)paint
Bioluminescence(li
ght produced by
living organisms)
Chemiluminescent
(light energy released by chemical
reactions)glow sticks
Chemiluminescence Movies
(Shackwave/Flash)
firefly light
Chemical energy ---? Visible light
energy
UV Light Technologies Light and
Color
Other sources of Light Energy can come from the Earth's minerals including:
THERMOLUMINESCENCE and TRIBOLUMINESCENCE
Light travels in straight lines, which allows us to use the ray model of light to explain certain properties.
A ray has a start point, from the light source, and moves in a straight line away from the source until it strikes
a surface.
If the surface is transparent, the light will continue in a straight path through the object
If the surface is translucent, the light will be diverted (refracted) after it passes through
If the surface is opaque, the light will be blocked and not allowed through the object
Light, Prisms, and the Rainbow Connection
Did you know that the light from the sun or from white electric lights is made up of all the
colors that can be seen by the human eye? In this activity you will use a prism to prove that
this is true. You will find that when you shine a light in just the right way on a prism, the light
enters the prism, bends (or refracts), and spreads out, showing us all of the beautiful colors
of a rainbow.
The rainbows we sometimes see in the sky work in the same way. When sunlight shines on raindrops in
just the right way, the sunlight is bent as it moves through the drops. It spreads out and is reflected back
to us as a colorful rainbow in the sky.
The group of colors that we can see with a prism or in a rainbow is called the color spectrum. These
colors always appear in the same order: red, orange, yellow, green, blue, indigo, and violet. An easy way
to remember the order of colors of the spectrum is to remember the name ROY G. BIV. Each letter of
the name is the first letter of a color.
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Science notebook
Prism
Convex lens
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Flashlight
White paper
Activity Directions
1. Before you begin, try to guess exactly how you will make a color spectrum with a flashlight,
prism, convex lens, and a piece of white paper. Answer these questions in your science
notebook and then share your predictions with your partner or group.
Where on the prism should you shine the light?
Where on the paper will you see the spectrum?
2. Now use your materials to make the color spectrum appear on a piece of white paper. This
works best when the room is very dark and the flashlight very bright. Can you identify all of the
ROY G. BIV colors in your spectrum?
3. Compare your color spectrum with the spectrums other students have made. Which is the
brightest?
4. In your science notebook, write a description of the best way to make a color spectrum with a
prism. Draw a picture showing the flashlight, prism, convex lens, paper, and the color spectrum.
5. Using an encyclopedia, science books, or the Internet, find out exactly how rainbows are
formed. In your science notebook, describe in writing how light moving through raindrops can
make a rainbow. Include a diagram.
6. In your science notebooks, write down any questions you still have about rainbows and how
rainbows are formed.
Lesson 2 - Shadows
When light hits an object, the light will either pass through it, be absorbed by it or bounce off it.
Steps:
1. Go outside on a really nice sunny day.
2. Find a nice sunny spot to stand. Make sure you find an open area where there are no objects such as
buildings or trees in the area.
3. Locate the position of the Sun in the sky and turn away from it so that your back is to it.
4. Look for your shadow in front of you.
5. Record the time and write what your shadow looks like. Is it a long shadow or is it and short shadow.
6. Go outside to the same position a few more times in the day and record the time and observation of
your shadow.
7. Be sure to go outside in the evening when the Sun has set and look for your shadow. Record your
findings.
If the Sun is low in the sky your shadow will look long.
If the Sun is high in the sky your shadow will look short.
Transparent materials will allow most of the light to pass through it.
Translucent materials will allow a lot of the light to pass through it.
Opaque materials will not allow any light to pass through it.
Please use the following link to learn about shadows:
http://www.schorsch.com/en/kbase/glossary/penumbra.html
http://www.mreclipse.com/Special/LEprimer.html
Lesson 3 – Reflection of Light
To learn about the reflection of light, we are going to start with a few lab/demo exercises. Please be
sure to following directions in each one and remember that we are using a light source, not necessarily
the laser light each one asks for.
Lab 1: Mirrors and Images
What is it that lets us see objects? Some objects, such as the sun, give off their own their own light.
Most objects, however, do not. These objects must reflect light in order to be seen. For instance, the
walls in the room do not put out their own light; they simply reflect light from overhead lights or from
sunlight that enters the room through a window. Smooth, polished surfaces, like mirrors, are very good
at reflecting light.
When you place an object between two hinged mirrors, light from the object bounces back and forth
between the mirrors before it reaches your eyes. An image is formed each time the light bounces off a
mirror. The angle between the two hinged mirrors has a special relationship with the number of images
you see. Try to find out what it is!
Required Materials

Science notebook, A pencil or some other object, such as a coin or paper clip, 2 4 x 6-inch
mirrors, Masking tape, Paper, Protractor
Activity Directions
1. Work with a partner. Take two mirrors and place them together with the shiny sides facing one
another. Tape them along the side to form a hinged door. The mirrors should be able to open
freely like a book.
2. Take a piece of paper or cardboard. Using a protractor, measure and mark angles (by drawing a
line) of 180 degrees, 90 degrees, 60 degrees, 45 degrees, 36 degrees, 30 degrees, and 20
degrees.
3. Place the hinged mirrors at each of these angles and put an object (it could be a coin, a pencil,
an eraser, or some other item you may have at your desk) between them as close to the mirrors
as possible.
4. Count the number of images you see and record your observations in your science notebook.
5. When you are finished, answer the following questions in your science notebook:
What happened to the number of images you saw as you changed the angle from 60
to 45 degrees between the mirrors?
What happened to the number of images you saw as you changed the angle from 30
degrees to 60 degrees?
Can you now make a statement about how the angle between the mirrors determines
how many images will be produced?
Compare your findings with the findings of other groups. Is the information the same?
If not, then what do you think might be the reason for them being different?
If you were to do this experiment again, what would you change and why?
Lab 2: Mirror, Mirror on the Wall: Angles of Reflection
Have you ever wondered why you can see your face in a mirror? This occurs because mirrors are very
smooth and shiny. Light bounces, or reflects, off of the smooth and shiny surface of mirrors. When you
see your face in a mirror you are seeing light from your face reflecting off of the mirror.
The way light bounces off mirrors is very much like the way a ball bounces against a hard surface. You
can throw a ball straight down, and it will bounce straight back at you. Or, you can bounce a ball at an
angle and it will bounce off the floor at the same angle away from you. Light reflects the same way off of
a mirror. In other words, light reflects from a mirror at the same angle as it arrives.
Required Materials
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Science notebook
4 x 6-inch mirror
Masking tape
Paper
Activity Directions
1. You need to work with a partner to do this activity. Find a place where there is a wall with plenty
of space around it. Attach the mirror at eye level on a wall with masking tape. Cover the mirror
with a piece of paper.
2. Now, both you and your partner should try to guess where you both need to stand to see each
other's reflection on the mirror. When you both agree on the places, mark them on the floor
with 6-inch pieces of masking tape.
3. Remove the paper from the mirror. Stand at your chosen place to determine if you can see each
other in the mirror.
4. If you can't see each other, try different places until you can. Mark the places that work with the
6-inch pieces of masking tape.
5. Next, place long pieces of masking tape on the floor from the center of your 6-inch place
markers to the wall straight under the center of the mirror. These should be straight lines.
6. Look at the angles made by the taped lines on the floor and the wall to see if they are the same
size. Remember that light bounces off a mirror at the same angle that it arrives. Therefore,
when the light from your face travels to the mirror on the wall, it should bounce off the mirror
at the same angle to the eyes of your partner.
7. In your science notebook, write a description of what you did in this activity. Include a diagram
with lines showing how light reflects off a mirror.
Lab 3
Materials Required:
Plane mirror with a vertical mount; protractor (or photocopy of a protractor); light.
Description of Procedure:
A plane mirror is placed in an upright orientation on a photocopy of a protractor. It is carefully
aligned so that its reflecting surface is flush with the line on the bottom of the protractor. A
leveling laser is set to LINE setting and placed with its flattest edge on the sheet of paper. The laser
line is directed at the origin of the protractor and reflects off the mirror. The path of the light is
clearly evident on the paper since the LINE setting is being used. Students somehow document the
path of the laser on their paper. The process is repeated for other angles of approach until
sufficient evidence has been accumulated in order to answer the question posed in the Purpose of
the lab.
Lab 4
Materials Required:
Plane mirror with a vertical mount; cardboard sheet; push pin; laser light; sheet of paper; ruler or
straight-edge.
Description of Procedure:
A line is drawn across the middle of a sheet of paper. The sheet of paper is placed on the cardboard
sheet. A plane mirror is placed in an upright orientation on the sheet of paper. The reflecting
surface of a plane mirror is aligned with the line. A push pin is pushed through the paper into the
cardboard at a location of about 8-10 cm from the mirror. A leveling laser is set to LINE setting and
placed with its flattest edge on the sheet of paper. The laser line is directed such that it passes
through the push pin, hits the mirror and reflects. The path of the light is clearly evident on the
paper since the LINE setting is being used. Students document the path of the both the incident
and the reflected light on their paper. The process is repeated for two other unique laser paths.
The laser is turned off and the mirror is removed. The three reflected rays are traced backwards to
an intersection point. Students make measurements of the image distance and the object distance
and answer the question posed in the Purpose of the lab.
Lab 5
Materials Required:
Laser; plane mirror; piece of paper; plane mirror; water mister or fog in a can.
Description of Procedure:
Students obtain a laser and set it to BEAM setting (as opposed to LINE setting). A plane mirror and a
sheet of paper are placed on the table; the mirror is facing the ceiling. The laser beam is directed at the
mirror. The location of contact is carefully observed. Students look at the ceiling and view the
appearance of the laser on the ceiling. The procedure is repeated for the mirror. Observations are
recorded in words and/or a diagram. When requested by students, the teacher visits the table and uses
a spray bottle of water to spray mist into the air in order to illuminate the incident and reflected rays for
the mirror and for the paper. Observations are made of the beams and of the presence or absence of a
laser dot on the ceiling. Students document all their observations using words and/or a diagram
So at all of these stations we used a mirror and looked at the angle of incidence (light going into the
mirror) and the angle of reflection (light coming from the mirror). We used a protractor to measure the
angles in some cases and we should have found the angles are equal.
http://www.photoflexlightingschool.com/Lighting_Principles/Secondary_Reflectors/Angle_of_Reflectio
n___Angle_of_Incidence/1113348874_r1.jpg
How do we use the reflection of light in real life? For instance, mirrors on a car?
Please complete Line master 2-8, and 2-9.
We reflected light with the use of mirrors which are clear, smooth surfaces. Would it make a difference
if we used rough surfaces? Say we used different colour surfaces?
To test this, you will try to reflect light off of a smooth piece of tin foil, and crinkled piece of foil. While
completing this, we will try to fill in line master 2-10 after we create a plan for us to complete this
experiment.
When the light hit the smooth tin foil, the reflection is called specular because the reflection occurred
according to the law and the angle of incidence equalled the angle of reflection. The crinkled foil did not
seem to follow this, but rather the light scattered a little more. This is called diffuse reflection. This
scattering of light allows you to see images on a page because when light hits white paper and reflects in
all directions, it reaches your eyes and you see white paper. An ink letter on the page does not reflect
any light, so no light from the ink reaches your eye, meaning you will see the letter against the white
background.
Light coming from a light source is called an incident ray and the light that bounces off the surface is
called a reflected ray. A line that is perpendicular ( 90o with the surface) to the plane mirror is called
the normal line. The angle between the incident ray and the normal line is called the angle of
incidence ( i ). The angle between the reflected ray and the normal line is called the angle of
reflection ( r ).
Using Reflections
Reflectors help to make bicycles and cars visible at night. A reflector is made up of hundreds of tiny, flat
reflecting surfaces arranged at 90o angles to one another. These small surfaces are packed side by side
to make the reflector. When light strikes the reflector the light bounces off the tiny surfaces and
bounces back toward the light source. Pool players use the law of reflection to improve their game. Like
a light ray, a pool ball travels in a straight line. In a 'bank shot' the cue ball is bounced off the cushion at
an angle which enables the player to hit the target ball. This angle is calculated as the angle of contact
(with the cushion) is equal to the angle of impact (with the target).
Lesson 4 – Refraction of Light
To begin learning about refraction, you will need a 500ml beaker mostly filled with water and a pencil.
While holding the beaker at eye level, you will move the pencil around from the front of the beaker
(closest to your eye), to each side, to the back of the beaker. At each spot, you will need to make an
observation of the relative size of the pencil compared to the other spots. What did you notice about
the size of the pencil?
Now, we will do the same thing but keep the pencil on the outside of the beaker. Start with it in front,
look through the beaker to see the pencil behind and look for it on either side. Did the size appear to
change?
Please complete the refraction labs.
Taken and adapted from: http://www.edquest.ca/component/content/article/186/
Refraction is the process in which light is bent, when it travels from one medium to another. The light
will bend because the mediums have different densities, meaning the particles are packed together at
different amounts. How tightly the particles are packed changes the path of the light because in a
more dense medium the light moves slower. The Law of Refraction states that as light travels from
one medium to a more dense medium, the light will bend towards the normal. If light travels to medium
that is less dense, it will bend away from the normal. The new direction of the light is called the angle of
refraction. Refraction can also occur when light travels through air at different temperatures because
warm air is less dense than cool air and this refraction in air is called a mirage. The pools of water you
see on a hot summer day are often caused by this effect, because the air closer to the ground is hotter
than the air above it. As you approach these pools, they disappear - because they were never there.
Refraction Diagram
i - angle of incidence
r - angle of partial reflection
R - angle of refraction
Light slows down as it passes from air to glass, and so bends toward the normal. Glass is a more optically dense medium.
Light speeds up as it passes from glass to air, and so bends away from the normal.
When light passes from one medium to another at 0°, or directly along the normal, no refraction occurs.
Is That All There Is To Light?
What happens when light strikes a surface? ......
Type of behavior
Absorption
Reflection
Refraction
What happens to light striking a
surface
Energy Transformation
Bounces off
Travels through in a new direction
Nature of surface
What else happ
rough, dark, opaque
smooth, shiny
different transparent medium
some light is ref
some light is ab
some light is ref
Lesson 5 – Images
An image will form in a mirror because the incident ray, the normal line and the reflected ray all lie in
the same plane (an imaginary flat surface). The light reflects off all points on the object being observed
in all directions and the rays that reach your eyes appear to be coming from a point behind the mirror.
Your brain interprets the pattern of the light and the image appears to be the same size and the same
distance from the mirror as the object. This is true for all flat mirrors.
We know that many mirrors are curved. Convex mirrors are those that bulge out, while concave mirrors
are those that cave in. Please complete Line Maser 2-12 with the use of the mirrors in the classroom.
What purposes do these mirrors serve for us?
Convex mirrors – images appear smaller and farther away than the object, reflect from a large area and
are useful in security devices.
Concave mirrors – images appear closer than actually are and can reflect from a large area and often
used as mirrors on cars.
We do not always use only mirrors to form images, we can also use lenses. We will use this link to start
looking at lenses:
http://www.pa.msu.edu/courses/2000spring/phy232/lectures/lenses/images.html
Please note that lenses are listed the same as mirrors in that convex means the lens bulges out, while
concave means the lens will cave in. They are also termed converging (convex because all rays of light
pulled to a focus after the lens) and diverging (concave because rays of light are spread apart). Which
type of image, real or virtual, goes with each lens?
Please complete the image labs.
Please complete the pinhole camera lab.
How do we use images and image creation in medicine? (Think of a an MRI)
Converging &Diverging Lens Diagram
optical centre (O) - the geometric centre of the lens
principal axis - a line drawn through the optical centre perpendicular to the lens surface
principal focus (F) - point where distant parallel light rays pass through a lens and come to a focus (or
appear to diverge from a focus in a diverging lens).
secondary focus (F') - a focal point on the opposite side of a lens from the principal focus. Since light can
pass from either direction or a lens may be flipped around, there are focal lengths on both sides of the
lens.
focal length - distance from the optical centre and the principal focus
focal plane - all focal points lie on the focal plane
Types of Converging Lenses
All converging lenses are thicker in the centre and thinner at the edges.
Diverging Lens


Principal focus (F) - is virtual because it is in front of the lens and the image cannot be projected
onto a screen.
Light rays appear to focus at F, but really diverge outward from the lens.
Types of Diverging Lenses
All diverging lenses are thicker at the edges and thinner in the centre.
Lesson 6 – Human Vision, Eye and Colour
To discuss how the human eye enables you to see things, we must first start with what the human eye
looks like.
Image courtesy of National Eye Institute, National Institutes of Health
Ciliary muscles - together with the suspensory ligament control the size of the pupil which lets in
variable amounts of light.
Suspensory ligaments - together with the ciliary muscles control the size of the pupil which lets in
variable amounts of light.
Cornea - the outer, transparent, dome-like structure that causes the initial refraction of light.
Iris - the colored ring of tissue behind the cornea and in front of the lens. The iris regulates the amount
of light passing by changing the size of the pupil.
pupil - the black aperture (hole) in the iris that lets light pass to the lens.
lens - a clear structure that refracts light onto the retina. The lens shape is controlled by the ciliary
muscles and suspensory ligaments.
sclerotic - the tough white surface of the eyeball
retina - the light sensitive region at the back of the eye that transmits the images you see to the brain. It
is composed of rods (sensitive to dim light) and cones (sensitive to bright light and color). There are 3
types of cones - ones sensitive to red, ones sensitive to blue and ones sensitive to green.
fovea - the concave centre of the retina that has the most concentrated area of rods and cones.
macula - part of the retina that is the central focusing spot. It is responsible for seeing details (such as
reading) and also for color vision.
optic nerve - a bundle of nerves that transmits the images from the retina to the brain.
blind spot - a spot at the back of the eye where the optic nerve is located. There is no retina at this point
so an image that forms here will not be seen.
vitreous humour - a clear jelly-like substance found inside the eye cavity.
A few question to consider:
1.
2.
3.
4.
5.
What kind of lens is found in our eye?
What controls the amount of light coming in?
Where is the image formed?
What kind of image is formed?
Can you draw a quick diagram to show how the image is formed?
How does this compare to how a camera makes an image?
As you can see from the diagram of the pinhole camera, an image is formed in a manner very similar to
that of your eye. In both cases, there is a lens and the image is a real image in the back of the eye or the
camera.
How do we see colours?
Colours get produced in two main manners, the additive and subtractive models. The subtractive
model gets started with this animation:
http://www.saskschools.ca/curr_content/physics20/optics/subtractive.htm
In subtractive colour models, white light hits an object and the majority of the light waves are absorbed.
The colour that is not absorbed, gets reflected back at you and is the colour you see. If all colours are
absorbed, you see black, not because it is reflected to you, but because no light has been reflected back
to you.
In additive colour models, primary colours are emitted directly from a source in some combination to
make you see other colours. Usually, the primary colours used are red, green and blue which when
mixed in equal proportions give you white light. The ratio of the mixture of the colours emitted
determines the colour that you see. This is how things like a computer monitor or TV work.
Based on these definitions, why do you think your clothes appear the colour that they do?
How do dyes work?
Can you explain how the human eye perceives the colours that you see?
http://www.ehow.com/how-does_5483906_human-eye-perceive-color.html
For information on colour blindness, we will use the following link:
http://www.saskschools.ca/curr_content/physics20/optics/color_blind.htm
Do all human eyes work the same? Of course not, we know this from looking around the room and
seeing that some people where glasses or have had some other corrective procedure done. I have had
laser eye surgery to correct my vision.
http://www.lasersite.com/Eyeworks/
How do we correct the problems? We use corrective lenses as follows:
Info taken and adapted from: http://www.saskschools.ca/curr_content/physics20/optics/eye.htm
The diagram below shows what happens with myopia or near sightedness.
The distance between the lens and the retina is too large (eyeball too long) or cornea-lens combination
refracts the light too much.
Distant objects are focused in front of the retina causing blurry vision. However, close objects usually
focus fine.
Corrected
A diverging lens in eyeglasses or contact lenses refracts light outward slightly.
Outward refracted rays are then bent by the cornea-lens combination so distant objects focus clearly on
the retina
The following diagrams shows what happens with far sightedness or hyperopia.
The eyeball is too short or the lens is too flat causing the light to not be refracted enough.
The image would appear behind the retina, thus near objects appear blurry. Distant objects focus fine.
Corrected
A converging lens in eyeglasses or contact lenses refracts the light slightly inward.
The cornea-lens combination then refracts the light so the image forms clearly on the retina.
These lenses can be put in front of the eye with the use of a set of glasses or contact lenses. When a
person get corrective eye surgery, the shape of the cornea is actual altered so that the image is focused
on the back of the eye.
Assignment: Please research one of the following topics and explain how it is used by people as well as
the process behind it. How are they able to work as they do?
1.
2.
3.
4.
5.
Night vision glasses
Snow Goggles
Telescopes
Polarized Sunglasses
Binoculars
6.
Lesson 7 – Impact of Electromagnetic Radiation
Notes are taken and adapted from: http://www.edquest.ca/component/content/article/191/
Light travels in straight lines. Sir Isaac Newton tried to explain why when he proposed that light beams
are made of streams of extremely tiny, fast-moving particles. These tiny particles of light, he suggested,
could only travel in straight lines, not around objects. When light passes through a small opening, it
spreads out around each side of the opening. To explain this, Dutch scientist Christiaan Huygens (16291695) suggested that light travels in a wave, not as a stream of fast moving particles.
The high parts of the wave are called crests, while the low parts of the wave are called troughs. The
distance from crest to crest is called wavelength (the distance from one complete crest and one complete
trough). The height of the crest or the depth of the trough from rest position is called the amplitude.
The Frequency is the rate at which the crest and the trough move up and down. The number of cycles in
a period of time - which is usually measured in hertz, or cycles per second.
Light Waves In Action
Sunsets can be explained using the wave model of light. As light waves from the sun travel through
Earth's atmosphere, they strike particles of different sizes, including dust and other elements. The longer
wavelengths of the reds and oranges tend to pass around these particles, whereas, the shorter
wavelengths of blue and violet, strike the particles and reflect and scatter. At sunset, the light we see
passes through about 700 kms of the Earth's atmosphere. There are many more particles in the
atmosphere at this time of the day, due to the activity going on during the day - so many more blue and
violet waves are reflected away. Red and orange are the vibrant colours we see at sunset.
Laser Light
In 1966, Theodore H. Maiman, a physicist at Hughes Aircraft Company in California became the first
person to use a process called ...
light
amplification by the
stimulated
or laser light.
emmission of
radiation
Incandescent lights give off many different colours and therefore have many different frequencies and
wavelengths. The waves are jumbled and crests from one wavelength might overlap the trough of
another, making the waves work against each other. This type of light is incoherent.
Laser light is quite different. It gives off a single wavelength (frequency) of coherent light.
Lasers have many useful applications:
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Scanners (bar codes in retail shops are scanned to give the price)
Digitized data are read by a laser on a compact disk (CD)
Lasers are use by law enforcement officers to detect the speed of vehicles.
Laser light can be released in pulses or in a continuous beam. In either form, it is so powerful,
that it can make precise cuts through metal and can also be used in surgery, as a scalpel - or, to
instantly seal broken blood vessels, because it produces such intense heat.
Eye surgeons use lasers to correct vision defects (shaving off areas of the cornea - to correct
problems caused by irregularities in the shape of the eyball)
They can also 'spot weld' a detatched retina
One day dentists may use lasers to vaporize cavities, instead of drilling into them.
Radiation in the Environment
Radiation is a natural part of our environment. Humans have always lived on earth in the presence of
radiation. Natural radiation reaches earth from outer space and continuously radiates from the rocks,
soil, and water on the earth. Background radiation is that which is naturally and inevitably present in our
environment. Levels of this can vary greatly. People living in granite areas or on mineralized sands receive
more terrestrial radiation than others, while people living or working at high altitudes receive more
cosmic radiation. A lot of our natural exposure is due to radon, a gas which seeps from the earth's crust
and is present in the air we breathe.
Radiation and Life
Radiation is energy travelling through space. Sunshine is one of the most familiar forms of radiation. It
delivers light, heat and suntans. We control its effect on us with sunglasses, shade, air conditioners, hats,
clothes and sunscreen. There would be no life on earth without lots of sunlight, but we have increasingly
recognised that too much of it on our persons is not a good thing. In fact it may be dangerous. so we
control our exposure to it. Sunshine consists of radiation in a range of wavelengths from long-wave infrared to shorter wavelength ultraviolet. Beyond ultraviolet are higher energy kinds of radiation which arc
used in medicine and which we all get in low doses from space, from the air, and from the earth.
Collectively we can refer to these kinds of radiation as lonising radiation. It can cause damage to matter,
particularly living tissue. At high levels it is therefore dangerous, so it is necessary to control our
exposure.
http://school.discoveryeducation.com/lessonplans/interact/electromagneticspectrum.html
Infrared Radiation
Red light has a wavelength of about 700 nanometers, but it could be stretched out to 100 nm, it would
become heat radiation, or infrared radiation. It would become invisible to the eyes, but you could sense it
with your skin. Anything that is warmer than its surroundings emit infrared rays.
Practical applications include:
motion sensors
burglar alarms
heat lamps
Radio Waves
If you could stretch the infrared wave out even further, so it became a few millimeters long, you could
get radio waves. Radio waves have a longer wavelength and a lower frequency than visible light. Different
types of radio waves have different uses.
Microwaves have the shortest wavelength and the highest frequency of the all the radio waves.
Microwaves have three characteristics that allow them to be used in cooking:
they are reflected by metal;
they pass through glass, paper, plastic, and similar materials;
and they are absorbed by foods.
Microwaves are used to detect speeding cars, to send telephone, satellite and television
communications, and to treat muscle soreness. Industry uses microwaves to dry and cure plywood, to
cure rubber and resins, to raise bread and doughnuts, and to cook potato chips. But the most common
consumer use of microwave energy is in microwave ovens. Microwave ovens have been regulated since
1971.
Remote Imaging Technologies
Radio waves are around us all the time. The signals from radio stations, television stations, cell phones
and even distant stars pass through your body every day.
LANDSAT is another
RADARSAT is a Canadian
Canadian satellite that
telecommunications satellite, which,
records how different
from time to time, sweeps the ground
parts of the light from
below it with radio waves, penetrating
the Sun reflect back to
fog, haze, clouds and rain. Their
the satellite. It's most
reflection back to the satellite give
important use is for
scientists information they can use in
agriculture, monitoring
their studies of the Earth.
crops for damage by
disease, pests and
drought.



Monitoring ice floes, which can
endanger ships
Search possible sites for
minerals, oil and natural gas.
Monitoring a flood, so that
sandbagging efforts can be
maximized where it is needed
most.
Ultraviolet Radiation
Just beyond the violet part of the visible spectrum are wavelengths of about 200 nm. , known as
ultraviolet (UV) radiation. This radiation is very energetic. It causes tanning, but it can also do irreparable
damage to us.
UV rays can ... damage the cornea of the eye (fogging which can lead to a slow loss of vision)
In more recent years, more UV radiation is reaching us because the ozone layer in the atmosphere (which
protects us from the damaging radiation by absorbing the UV rays) is being thinned. This thinning of the
ozone layer is speeded-up by the use of aeorsol sprays and Freon gas, which break up the ozone particles.
X-Rays
Even shorter wavelengths with higher frequencies are the X-rays. These waves pass through tissue (skin
and muscle) and are absorbed by the bones. This radiation always stays in the bone and builds up over
time. Therefore people who work as technicians taking the x-rays must protect themselves, by leaving
the room where the xray is taken and also protect the patient's other areas of the body with lead vests to
prevent over-exposure.
Gamma Rays
Gamma rays have the shortest wavelength and the highest frequency of all the waves in the
electromagnetic spectrum. Gamma rays result from nuclear reactions and can kill cells. This can be useful
if the cells being destroyed are harmful - like cancerous cells. The cancerous growth of cells and tissue
can be radiated, using gamma rays, and is known as radiation therapy.
Are there risks to the use of cell phones?
http://cprnews.com/articles/cnncancer/WHO:-Cell-phone-use-can-increase-possible-cancer-risk.html
http://news.cnet.com/8301-1035_3-20067724-94/cell-phones-and-the-radiation-risk-roundup/
http://www.cnn.com/2011/HEALTH/05/31/who.cell.phones/index.html