31415Science 8

Unit 2 Optics and Vision

1. Light travels in straight lines. When it leaves a luminous source, it travels outward in every direction so that light “fills” the whole room or area being lit.

When light strikes an opaque object, some of the light is reflected from the surface, and some is absorbed. Examples of opaque objects are your desk and chair, people, and the books on your desk. We see objects because of the light reflected off their surfaces.

When light strikes a transparent object, it passes through the object. It may be bent as it enters and leaves the transparent object. This makes objects appear to bend, as a pencil does in a beaker of water. Some examples of transparent objects are glass and water.

Some objects are translucent. Translucent objects allow some light to pass through, but absorb and reflect some as well. Examples of translucent materials are stained glass, frosted glass, thin fabrics such as chiffon, and tissue paper.

2. Because light travels in straight lines, it produces shadows when its passage is blocked by an opaque object. Shadows have fully shaded areas called the umbra, and partly shaded areas called the penumbra. The penumbra is formed by some of the light near the edges of the object being bent as the light passes by, and by reflection of some light from other objects surrounding the opaque object.

3. A pinhole camera is a simple device that focuses the light from a bright object to produce an image on a screen, such as the translucent lid of a coffee can or Pringles chip can. We can draw ray diagrams to show how the light travels and how the image is formed. A ray diagram shows the path of a single beam of light as it travels from the source of the light.

4. Illuminance is the amount of light reaching a surface per unit area. It can be measured in lumens per square meter. Luminance intensity, or luminous intensity, as it is sometimes called is the brightness of light. Luminance intensity becomes less and less as you move away from a light source.

5. A telescope can receive small amounts of light from far out in space because no matter occupies space and gets in the way of the light from very distant stars. The light that reaches a telescope on earth may have travelled through space for years before it reached the earth.

6. Light pollution occurs when lights from cities, airports, industries, etc. emit light up into the atmosphere where the light reflects off dust particles and cloud and forms a glow above the area. Light pollution makes it difficult to see stars or the Northern Lights in a city.

7. Luminous objects are objects that produce their own light. Examples are the sun and stars, fires, and light bulbs. Non-luminous objects are objects that do not produce their own light, but may reflect light from luminous sources. We see luminous objects because of the light they produce, and we see non-luminous objects because of the light they reflect.

Mirrors

1. Plane mirrors: these are flat mirrors. They are made of glass with a shiny, reflective backing. Early mirrors were made of polished metals or rocks and have been in use for thousands of years. The glass, silver-backed mirrors that we use today were developed in Italy in the early Renaissance.

A plane mirror reflects incoming light back from its surface in parallel undeflected rays, so that the image we see looks exactly like the object in front of the mirror. Right and left sides are reversed, but the image formed appears to be the same size, upright, and an equal distance behind the mirror as the object is in front of the mirror. Images that we see in mirrors are called virtual images. We cannot capture a virtual image on a screen; it always appears to be “behind” the mirror.

When light is directed at a plane mirror, it strikes the mirror at an angle called the angle of incidence. When it reflects from the mirror, it reflects at an equal angle called the angle of reflection. Angles are measured from an imaginary line perpendicular to the mirror surface called the normal. The law of reflection states: “The angle of reflection of light from a plane mirror is equal to the angle of light incident on the mirror.”

Specular reflection occurs when light reflects from a very smooth surface. The light rays are reflected parallel in specular reflection.

Diffuse reflection occurs when light reflects off a shiny uneven surface, such as the ocean, or a lake on a windy day. Because the surface is uneven, light reflects off of it in many directions, and the light is scattered. In effect, the light forms many, many “normals” at many angles.

One application of diffuse reflection is in cut glass or crystal light shades. These shades cause light from the bulb to scatter throughout a room, instead of shining in just one area.

Plane mirrors enable us to study our reflections. We use them to see what we look like. The other uses of mirrors include seeing “around corners”, like a dental mirror, seeing behind us, as in a rear view mirror, and seeing an image on a slide, as in a microscope. In these situations, the main use of the mirror is to send light in a different direction so we can see an image.

In order to see your complete image in a plane mirror, the mirror must be at least one half your height, and it must be hung at the correct height. You can see more of your image and your surroundings if you are further away from the mirror. A plane mirror reverses the right and left side in the image. If you hold a pencil in your right hand, your image will appear to be holding it in the left hand.

2. Curved Mirrors: Concave and Convex Mirrors

a) Concave mirrors: these mirrors dish inwards, so you seem to be looking into a polished bowl. A concave mirror reflects light inward toward a focal point. It can produce two kinds of images: real images that can be seen on a screen, or virtual images that can be seen only in the mirror.

b) Some mirror terms:

1. Principal axis: an imaginary line that is perpendicular to the center of the mirror, like a normal on a plane mirror.

2. Focal point: the point on the principal axis where all the rays striking the mirror come together. A clear image of a bright light forms at the focal point.

3. Center of curvature: if the curved surface of the mirror was continued to form a complete sphere or ball, this would be the very center of the ball. The center of curvature is called C, and C is twice as far from the mirror as the focal point. C = 2 F.

4. Real image: an image that you can see on a screen. All real images from concave mirrors are upside down, or inverted.

5. Virtual image: an image that can only be seen by looking in the mirror. Virtual images appear to be behind the mirror. Virtual images are always right side up. If you place an object between the focal point and a concave mirror, the image will be virtual.

6. Optical bench: an apparatus made of a meter stick, with mirror and lens holders, which can slide on the meter stick. The optical bench is used to find the distance to the object and the image from the center of the mirror.

7. Characteristics of the image: a description of an image formed by a mirror or lens which should include the following information: is the image real or virtual? Is the image larger or smaller than the object? Is the image upright or inverted?

8. Convex mirrors: these mirrors bulge outward in the center. Convex mirrors only form one kind of image: virtual images which are upright and smaller than the objects. This is because a convex mirror scatters light from its surface, and the rays appear to come together or converge behind the mirror. Convex mirrors are often used for security mirrors in businesses. They give a wide view of the surroundings.

9. Convex lens: a convex lens bulges out in the center. Like all lenses, it lets light shine through it. But as the light shines through it, it is bent and focused on a point, in the same way that a concave lens focuses light. Images formed by convex lenses are like images formed by concave mirrors: they are real and inverted.

10. Concave lens: a lens that dishes in in the center, and forms images like a convex mirror: virtual, upright and smaller than the object.

What are the images formed by concave mirrors like?

1. If an object is placed more than two times the focal length from a concave mirror, the image will be real, inverted and smaller than the object itself.

2. If an object is placed at 2F, the object and image will be the same size, the image will be real, and it will be inverted. The image will form at 2F.

3. When the object is placed between F and 2F, the image is real, inverted and larger than the object.

4. When an object is placed at F, no image will form because the light is reflected back in parallel rays that never cross.

5. If the object is placed between F and the mirror, the image will be virtual, upright, and larger than the object.

What are images like from a convex mirror? These mirrors are like the security mirrors in a business. All images that form in these mirrors are the same: they are virtual, upright, and smaller than the objects.

Concave Mirror Lab

In this lab, you will use an optical bench and a concave mirror to find the characteristics of images formed by the mirror.

1. Locate the focal point of your mirror by finding the clear image of the window on your screen. Record the distance from the mirror to the clear image here: focal length = __________________ cm.

2. Calculate the values of (2.5) F, (2.0) F, (1.5) F and (0.5) F and enter them in the data table below.

3. Data Table

Observation # Object Distance Image Distance Characteristics

4. Place your mirror at one end of your optical bench. Place your candle at 2.5 F, and move your screen back and forth to find the best clear image. Record the distance from the mirror to the image in your data table.

5. Repeat step 4 but placing the candle at 2.0 F, and record the image distance again. Repeat for 1.5 F, F, and 0.5 F. Each time, locate the image if possible and record the image distance in your data table.

Questions:

1. At which object distance(s) was it difficult or impossible to see and image of the candle?

2. At which object distance was the image the same size as the candle?

3. At which object distance was the image a virtual image? (When could you only see the image in the mirror?)

4. When was the image larger than the object? When was it smaller than the object?

Uses of Concave and Convex Mirrors

Concave Mirrors

DeviceUse of Concave Mirror

1.

2.

3.

4.

Convex Mirrors

DeviceUse of Convex Mirror

1.

2.

3.

4.

From Air to Glass Activity

(pp 116-117, text)

Q: What happens to light when it passes from air into glass?

Materials: ray box, glass block, paper, ruler, protractor

Procedure:

1. Place glass block in the center of a sheet of paper and trace around it. Mark the center of one side and draw a normal from that point that is perpendicular (90 degrees) to the block surface. Label this line “Normal”.

2. Turn off the lights and shine the ray box at your glass block so that the rays are parallel to each other before they reach the block.

3. Shine the ray directly along the normal and observe where the ray enters and leaves the block. The ray should pass straight through the glass without bending.

4. Shine the light at an angle so it enters the block exactly where the normal touches the block. Mark the ray before the block, and mark where it leaves the block on the opposite side and its pathway after it leaves the block.

5. Repeat this process for 3 more angles, marking the incoming or incident ray, and the outgoing or refracted ray for each angle. Be sure to number the rays as you mark them.

6. Remove the glass block. Connect the points where each ray enters with the point where each ray exits the glass block. See the diagram above. You should have three rays marked on your diagram. Each ray should have arrows to show its direction.

7. Measure the angles of incidence from the normal, and record the angles in the data table. On the opposite side of your glass block draw a new 90 degree normal at the point where each ray leaves and measure the refracted angles for each ray. Record those angles as well.

Data Table

Ray NumberAngle of Incidence Angle of Refraction

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

Do questions 10-14 on page 117 of your textbook.

Convex Lens Lab

Problem:

What are the characteristics and locations of the images formed by an object in front of a double convex lens?

Materials:

Optical bench

Converging lens and holder

Light source

Screen

Procedure:

1. Hold the lens in a dark part of the room so the image of the window is clearly focused on the screen. Record the distance between the screen and the lens as F, the focal length. Reverse the lens so that the light is coming from the opposite direction, and check to make sure that F is equal on both sides.

2. Calculate and record the values of 2.5 F, 2.0 F, 1.5 F and 0.5 F in your data table. These are the distances you will place your candle from the lens.

3. Place the lens in the exact center of the meter stick. Mark the distances you recorded on the meter stick with tape or chalk.

4. Place the object at 2.5 F. Move the screen back and forth until you find the best and clearest possible image. Note and record the image distance, and the size and position (upright or inverted?) of the image.

5. Repeat the process in #4 for the other object distances, and record the image distance, whether it is real or virtual, and the size and position of the image.

6. As you repeat steps 4 and 5, answer these questions:

a) What happens to the size of the image as you move the object closer to the lens, i.e. from 2.5 F to 1.5 F?

b) At what object distance is it impossible to get a clearly focused image?

c) At what object distance does the image become virtual rather than real?

Data Table

Observation #Object DistanceImage DistanceCharacteristics of the Image

SizeAttitudeType

1 2.5F

2 2.0 F

3 1.5 F

4 F

5 0.5 F

7. Which of the object distances would produce the image similar to

a) A photocopier? (same size and real)

b) A magnifying glass? ( virtual and larger)

c) A slide projector? (larger and real)

d) A camera? (smaller and real)

e) A spotlight? (parallel light, no image forms)

Making a Pinhole Camera

A pinhole camera is a simple device that captures light through a pinhole and creates an image on a translucent screen. The image is upside down on the screen.

In its simplest form, a pinhole camera can be made from any opaque container, such as a coffee can, Pringles can, or even a cardboard box. They work best if the inside is painted black. Punch a small hole in the bottom of the container, and cover the open end with its translucent lid or with waxed paper. Measure the height of your camera container, and record the height in the chart below as “di”. Your camera is complete.

To use the camera, in a darkened room, hold the camera at arm’s length in front of yourself, and point the pinhole end at a bright object such as a candle or mini light bulb. Look for the image of the bright object on the translucent lid of the camera. You may have to move closer to or further away from the object to get a clear image. When you have the clearest image of the object, measure the distance from the pinhole to the object and record this distance as the object distance. Also measure the height of the object and the height of the image formed on the lid of your camera.

Observations:

Distance to object, do = __________ Length of camera, di = __________

Height of object, ho = ____________ Height of image, hi = __________

Eyes

Eyes and the ability to see vary greatly from one species to another. Humans are able to see straight ahead and off to each side (peripheral vision) quite well. Owls have very flat faces, so they have poor peripheral vision. However, they can swivel their heads around almost 180 degrees, so they more than make up for their eye position.

Horses and zebras have vision similar to humans, but because their eyes are on the sides of their heads, they are blind directly in front, but have great peripheral vision. Horses see two images of the world around them at all times. Deer have large eyes giving them good vision as well.

Cats and dogs have poor colour vision, but better night vision than humans. Cats and many other animals that hunt at night have a reflecting layer behind their eyes called the tapetum lucidum, which enhances vision in low light levels. All cat species have more rod cells and fewer cone cells than humans. This gives them sharper vision but less colour vision.

Birds of prey such as eagles and falcons have excellent binocular vision allowing them to see their prey from high above and from long distances.

Goats have weird rectangular pupils that give them a field of view of almost 330 degrees. They can see everything except their own backs. This is a protective adaptation that allows them to see predators such as cougars coming from all directions.

Chameleons have eyes that can swivel independently of each other, so they can look ahead with one eye while looking up with the other. They can process two different images at the same time.

Mantis shrimp have amazing vision, due to their compound eyes mounted on stalks. Their eyes are divided into 3 segments so they have trinocular vision, plus they can see 12 colour bands compared to humans who can only see 3!

Dragonflies have compound eyes made of thousands of individual lenses and also have three separate eyes known as ocelli, which help them detect and react to motion much faster than humans. Dragonflies are able to process the information much faster as well, so that it seems that they see in slow motion. This allows the dragonflies to capture mosquitoes and other insects on the fly.

Human eyes are highly effective optical organs, but there are differences in the forms and functions of eyes in all species, making them particularly adapted to that organism’s specific needs.

Human eyes

The parts of the eye and their functions

a) Cornea: clear thin sheet of cells that protects the iris and pupil surface and slightly focuses light as it passes through it.

b) Aqueous humor: a clear watery fluid between the cornea and the lens.

c) Lens: focuses light on the retina; found directly behind the pupil and iris.

d) Iris: regulates the amount of light entering the eye by controlling the pupil size and gives our eyes their colour

e) Pupil: a hole in the center of the iris through which light passes.

f) Vitreous humor: a clear jellylike substance that fills the eyeball from the lens to the retina and gives the eyeball its round shape.

g) Sclera: a tough white outer covering of the eye that covers the whole eye except for the cornea.

h) Optic nerve: this nerve carries messages from the retina to the hypothalamus or other part of the brain.

i) Retina: a delicate, multilayered, light-sensitive tissue that lines the eye, and transmits the images it collects to the optic nerve. The retina contains two kinds of light-sensitive cells: rods, which absorb light and produce a clear image, and cones, which detect colour.

j) Blind spot: this is a section of the back of the eye where the optic nerve is attached to the retina. It has no rod or cone cells, so images do not form there. It is sometimes called the optic disk.

The Camera and the Eye

Cameras perform many of the same functions as eyes. Both collect light to form images. In both the light is focused by a lens. But there are differences as well.

The lens in the eye can change shape to focus light from large or small distances on the retina. The camera needs a shutter to control the length of time the light enters the camera or else the image on the CCD matrix will be overexposed. The retina doesn’t become overexposed, because the image is transmitted through the optic nerve in about 1/24th of a second.

The aperture and the pupil both allow light in. In cameras, the diaphragm changes the size of the aperture, and is similar to the iris of the eye. The shutter opens for a fraction of a second to expose the film to light. Its function is similar to the eyelid of the eye. The CCD matrix of a digital camera receives the image and stores it as digital data on a media card. In the eye, the image formed on the retina is transmitted through the optic nerve to the brain and stored as a memory in the brain.

Light and Colour

Colour is a wonderful thing. Make a list of all the words you can think of that you might use to describe a colour. (“Bright, intense, soft, smoky, . . . . ) From your list circle all the words you used that have to do with light.

Light is necessary in order to see colour. “White” light is made up of all the colours of the spectrum: red-orange-yellow-green-blue-indigo-violet (ROYGBIV)

When we shine a beam of light through a prism, it splits into all the colours of light in the spectrum. We can do the same thing by looking at a bright light source with a spectroscope. If we combine two prisms, one right side up and one upside down, we can first separate the colours and then re-fuse them back together again. The colour spectra we are most familiar with are rainbows and sundogs. Sundogs form when ice crystals in the air act like many tiny prisms, and rainbows form when water droplets in the air do the same thing.

The visible light spectrum (ROYGBIV) produces all of the colours we see. It’s amazing that just these 7 colours of light can produce all the thousands of different colours we can see. When we mix paints together, such as blue and yellow, we get green paint. When we mix blue and red paints, we get purple. Does the same thing happen with colours of light? Read over the lab on page 140-141 of your text, and predict what will happen if you combine different colours of light.

The primary colours of light are red, green and blue. These are the three colours of light that the cone cells in our retinas can distinguish. Combining pairs of these primary colours of light produces the secondary colours of light. R + G = yellow. B + G = cyan. R + B = magenta. Combining all three colours of light produces white light. This is called the addition model of colour, because we create the colours by adding the light together.

The subtraction model of colour is just the opposite. We see the colours of objects because the objects absorb or subtract some colours of light, and reflect the remaining colours to our eyes. We see only the reflected colour. For example, we see green paper because the chemicals in the paper absorb or subtract the red and blue light. Only the green light is reflected to our eyes. We see red paper because the chemicals in the paper absorb or subtract the green and blue light so the red only reaches our eyes. When we see yellow, it is because the blue light is being absorbed and a mixture of the red and green are reflected to our eyes. We see cyan when the red light is absorbed and the blue and green are reflected off the surface. In each case, some of the colours of light are removed by being absorbed by the object. We see the colours that remain because those colours are reflected to our eyes.

When we see black, it is because all the colours of light are absorbed. The colour black is really the absence of light entering your eyes.

When we see something that is white, it means that all of the colours of light are being reflected, and none of the light is being absorbed by the object.

This rule explains why wearing black clothing makes you warmer in summer, and wearing white helps to keep you cool. The light that is absorbed by black clothing is converted into heat energy, making you too warm. The light reflected by white clothing keeps heat energy away from your body, making you cooler.

What are pigments? Pigments are chemical compounds that absorb certain colours of light and reflect others. They subtract part of the light, and reflect the colour of light that we see. The primary colours of pigments are different than the primary colours of light. They are magenta, cyan and yellow. We see magenta when red and blue light are reflected and green light is absorbed by the pigment. We see cyan when green and blue light are reflected and red is absorbed by the pigment.

We see yellow when red and green light is reflected and blue is absorbed. See the diagram on page 147 of your text. How are light colours and pigment colours related? The primary colours of pigments are the secondary colours of light. This is because pigment colours are formed by absorption or subtraction of a colour of light.

Electromagnetic Radiation

The electromagnetic radiation spectrum is the complete range of the wavelengths of electromagnetic radiation, beginning with the longest radio waves (including those in the audio range) and extending through visible light (a very small part of the spectrum) all the way to the extremely short gamma rays that are a product of radioactive atoms.

All electromagnetic radiation can travel through empty space. It travels at the speed of light, which is 300 000 000 m/s, or 300 million meters per second. EMR travels as waves of radiation. Waves have properties including speed, wavelength and frequency.

Wavelength is the distance between one crest or peak of a wave and the next crest or peak. Wavelength is measured in meters.

Frequency is the number of crests that pass a particular point each second, or waves per second. Frequency may be measured in Hertz, Hz. One Hz = one wave/second.

Speed of waves can be found by multiplying wavelength x frequency. Speed is measured in m/s.

Another property of waves is the amplitude of the waves or their height. The greater the amplitude, the greater the energy carried by the wave.

Various forms of electromagnetic radiation have various uses and effects on living organisms. Some, like gamma rays, are very dangerous, while others, such as infrared radiation, are very helpful. Generally, shorter waves with higher frequencies cause more damage to humans and other living organisms.

Remember all you’ve learned about light: light is a form of energy; light travels in straight lines; light can be reflected and refracted; light spreads outward in every direction from a source; light can be split into the colours of the spectrum; light can be detected by our eyes.

Now add this to what you know about light: light is a form of electromagnetic radiation. It travels in waves, through empty space, all the way from the sun to reach the earth. The sun is 150 000 000 kilometers away, and it takes about 8 1/3 minutes for light to reach us from the sun.

Light that we can see is only a tiny part of the complete electromagnetic spectrum. This is called the visible spectrum. The wavelengths of visible light range from about 400 nanometers to 700 nanometers. A nanometer is 1 millionth of the thickness of a dime, a very tiny measurement! Like all electromagnetic radiation, light travels at 300 000 000 m/s. Light waves travel in straight lines, and are reflected and refracted just as we learned earlier.

We cannot see any of the forms of electromagnetic radiation except visible light. We can certainly feel the effects of infrared radiation, because infrared radiation is actually heat. Ultraviolet radiation is on the other side of the visible spectrum, and is the kind of EMR that causes sunburn and skin cancer.

Questions

1. What is electromagnetic radiation? Look this up in a dictionary. It’s not in your notes!

2. What is the electromagnetic radiation spectrum?

3. All electromagnetic radiation can travel through__________________.

4. If we know the wavelength and frequency, how can we find the speed of a wave?

5. How fast does EMR travel in a vacuum?

6. If the waves on a lake are higher on a windy day, does that mean they have shorter wavelengths or greater amplitude?

7. What form of electromagnetic radiation (EMR) has the longest waves?

8. What does AM and FM stand for in radio waves? (see your Text book)

9. What form of EMR has the shortest waves?

10. What is the speed of light?

11. Define the terms: wavelength, speed, amplitude, crest, frequency.

12. Which forms of EMR could be used to cook your food?

13. What form of EMR is used to examine a broken bone?

14. What form of EMR can you hear on Fox radio?

15. What form of EMR is given off by uranium ore?

16. What form of EMR causes sunburn?

17. List the properties of light.

18. What is the common name of infrared radiation?

Test: Outcomes 1 to 3Name: ________________________

True or False. Write the WORD true or false in the blank.

__________ 1. If light strikes a mirror at an angle of 23 degrees, it will reflect back at an angle of 67 degrees.

__________2. As you move away from a lamp, the illuminance becomes less.

__________3. A concave mirror can create a real image.

__________4. All images produced by convex mirrors are virtual images.

__________5. Plane or flat mirrors produce real images.

__________6. In order to see all of your image in a plain mirror, it must be half your height.

__________7. When light passes from air into oil, it slows down.

__________8. A concave lens bends light inward so it focusses on a point.

__________9. A convex lens bends light inward so it focusses on a point.

_________10. Bending of light rays as they enter a different substance is called reflection.

(10 marks)

Fill in the blanks. There is a word box below.

1. A line drawn at 90 degrees to a mirror is called a ________________.

2. A substance that prevents any light passing through it, is _____________.

3. If an image can only be seen in a mirror, it is a _____________ image.

4. Reflection off of smooth surfaces produces regular or _____________ reflection.

5. Light reflecting off of a rough shiny surface produces _______________ reflection.

6. A ________________ image can be seen on an optical screen.

7. A substance like clean water that allows light to pass through freely is called a _________________ substance.

8. When light passes through a triangular prism, it splits into a rainbow or ________________ of colours.

9. The mirror at the back of a drugstore is a ________________ mirror.

10. A microscope uses a series of ___________ to magnify the image of a specimen.

(10 marks)

Short Answer Questions. Answer in the space provided. (3 marks each)

1. Explain how you could increase the amount of light the plants in a flower bed on the north side of your house receive.

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. A student states: “My image in a plane mirror is identical to me”. Is the student correct? Explain your answer.

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Identify three devices that use both convex and concave mirrors and explain how they help to improve the images of objects.

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Diagrams: Use your ruler and protractor to draw a ray diagram of a ray reflecting off a mirror if the angle of incidence is 30 degrees. Label the angle of incidence, the normal, the angle of reflection and the mirror surface. (5 marks)

Word List

TranslucentDiffuseTransparentConvex

ConcaveOpaqueNormalSpecular

SpectrumLensesMirrorsReal

Virtual

Test: Outcomes 4.0-6.0Name: _______________________

Optics and VisionDate: ________________________

I. Multiple Choice. Circle the letter that best completes each sentence.

(10 marks)

1. The height of a wave from its middle rest position is called the

a) Frequency

b) Amplitude

c) Wavelength

d) Crest

2. The distance between the top of one wave and the top of the next wave is the

a) Crest

b) Trough

c) Wavelength

d) Frequency

3. The number of times a wave source vibrates in a certain time is the

a) Crest

b) Trough

c) Wavelength

d) Frequency

4. The highest points of repeating waves are called the

a) Crests

b) Troughs

c) Amplitude

d) Wavelength

5. Electromagnetic waves with the longest wavelengths are

a) Microwaves

b) X-Rays

c) Visible light

d) Radio waves

6. X rays are described as

a) High energy, long wavelength waves

b) High energy, short wavelength waves

c) Low energy, long wavelength waves

d) Low energy, short wavelength waves

7. Sunscreen lotions are used to prevent sunburn and skin cancers from

a) Infrared rays

b) Visible light

c) Ultraviolet light

d) Microwaves rays

8. The ability of fireflies and jellyfish to produce light is called

a) Fluorescence

b) Bioluminescence

c) Chemiluminescence

d) Phosphorescence

9. The openings of the eye and the camera that allow light to enter, in order, are

a) The pupil and the aperture

b) The diaphragm and the iris

c) The eyelid and the lens

d) The optic nerve and the CCD matrix

10. The primary colours of light are

a) Red, yellow, blue

b) Red, cyan, magenta

c) Red, green, blue

d) Cyan, magenta, yellow

II. True or false. Circle the letter T or F. (10 marks)

1. A rainbow is formed as sunlight enters single raindrops. T F

2. Red and green light combine to form blue light.T F

3. When light is reflected from a ripe tomato, the blue and green light is reflected and the red light is absorbed.T F

4. The secondary colours of light are formed by mixing two primary colours of light.T F

5. When you mix all the colours of light together, the resulting colour is black.

T F

6. Another name for ultraviolet light is heat.T F

7. Compact fluorescent lightbulbs produce a lot of waste heat. T F

8. The visible spectrum includes ultraviolet and infrared light. T F

9. EMR that has short wavelengths has higher frequency.T F

10. The camera forms a real image.T F

III. Short Answer Questions. Answer in complete sentences in the space provided.

1. Colour this colour wheel, showing the three primary colours of light, and the secondary colours of light produced where the primary colours overlap. Label all of the colours. (6 marks)

2. Compare the human eye with a camera. State three things that are alike in both, and two things that function differently. (5 marks)

3. There are 7 forms of electromagnetic radiation including infrared, microwaves, X-rays, ultraviolet, visible light, radio waves, and gamma rays. Place these 7 kinds of waves in order, beginning with the waves with the greatest energy and shortest wavelength, and ending with the waves with the lowest energy and longest wavelength. (4 marks)

4. You have three stage lights of equal intensity: red, green and blue.

a) Describe how you could project yellow light onto the white screen at the back of the stage.

b) If a person in a blue coat is standing onstage in the yellow light, what colour will his coat appear? (4 marks)

5. Compare the benefits and drawbacks of using compact fluorescent light bulbs to incandescent light bulbs in your home. (4 marks)