SNC 2D Light and Geometric Optics HOMEWORK Page 5 of 9
LIGHT AND THE ELECTROMAGNETIC SPECTRUM
1) In terms of heat transfer, how is radiation different from conduction and convection?
a. Radiation – occurs when energy (ie: heat) moves in waves in empty space; usually as electromagnetic waves
b. Conduction – occurs when heat moves from one object to another through direct contact with solids
c. Convection – transfer of heat through the movement of fluids; usually in liquids or gases
2) Write the electromagnetic waves in order from lowest energy to highest energy: infrared light, X-rays, red light, gamma rays, and microwaves
a. Microwave, infrared, red (visible) light, x-ray, gamma ray
3) Sunscreen, if used properly, can protect you from getting a sunburn. From which electromagnetic waves must sunscreen protect the skin?
a. Ultraviolet rays
4) List the seven colours that Newton identified in the visible spectrum of white light.
a. Violet, Indigo, Blue, Green, Yellow, Orange, Red
5) List some devices that you have used or plan to use today that involve electromagnetic waves.
a. Answers will vary.
6) Match each electromagnetic wave from column A with the term from column B that is most closely related:
COLUMN A
X- rays – baggage screening
ultraviolet light – vitamin D
radio waves - radar
infrared light - DVD remote control
microwaves - telecommunications
gamma rays - cancer treatment
visible light - theatre/concert effects
7) Briefly describe how you could demonstrate that white light is composed of many different colours.
a. White light can be separated into its different colors thorough a prism. Blue light refracted most; red light refracted least.
SOURCES OF LIGHT
1) In grade 9 science, you studied the differences among stars, planets, and moons. Which are luminous, and which are non-luminous? Explain why this second group is classified as non-luminous.
a. Second group is non-luminous because they do not produce their own light.
2) Why is an incandescent bulb a very inefficient light source? Only 5-10% is converted to visible light.
3) Name the process of producing light by passing an electric current though a gas. Electric Discharge
4) What is the main difference between phosphorescence and fluorescence?
a. Phosphorescence contains phosphorus containing compounds
b. Fluorescent lights contain mercury, more energy efficient
5) a) Do fluorescent whiteners, or optical brighteners, in detergents really make clothes cleaner? No, they make clothes ‘brighter.’
b) There is concern that extra additives in detergents can have negative health and environmental impacts. Is it wise to use detergents containing these additives? Explain. Answers will vary.
6) Predict whether or not a fluorescent material would glow if it was illuminated by infrared light.
7) Why is chemiluminescence also called “cold light”. – Little or no heat is produced. Ie: glow sticks
8) Predict whether or not a light stick would be a good light source in a potentially explosive environment. Explain your prediction.
9) State several reasons why living organisms might use bioluminescence. To lure prey, attract mates, defence mechanism.
10) What are two differences between LEDs and incandescent bulbs? LEDs are more energy efficient and have many uses. Ie: Christmas lights, traffic lights, indoor lights.
11) LEDs are considered an even better alternative to CFLs to replace incandescent bulbs. Compare CFLs with LEDs. Are LEDs a better alternative? Be sure to consider environmental, health, and economic factors. See Comparison Chart below:
LED / CFL / IncandescentLight bulb projected lifespan / 50,000 hours / 10,000 hours / 1,200 hours
Watts per bulb (equiv. 60 watts) / 6 / 14 / 60
Cost per bulb / $35.95 / $3.95 / $1.25
KWh of electricity used over
50,000 hours / 300 / 700 / 3000
Cost of electricity (@ 0.20per KWh) / $60 / $140 / $600
Bulbs needed for 50k hours of use / 1 / 5 / 42
Equivalent 50k hours bulb expense / $35.95 / $19.75 / $52.50
Total cost for 50k hours / $95.95 / $159.75 / $652.50
RAY MODEL OF LIGHT
1) What is the ray model of light?
a. It is a model of light that describes how light travels. It states that light travels in a straight line. A ray represents a single unit of light and is drawn as a straight single arrow.
2) Draw a simple ray diagram of light rays travelling out from a light bulb. See below:
3) What are two properties of light that you can show using a ray diagram?
a. Path the light is travelling
b. Direction of light
4) What three things can happen with light strikes an object?
a. Depending on type of material, light can be transmitted or absorbed:
5) Use a labeled ray diagram to show the difference between transparent, translucent, and opaque objects. See diagram above.
6) What determines how light rays behave when they strike an object?
a. Type of material ie: glass window vs. concrete wall
7) a) Name the two parts that make up most mirrors. Glass and a thin reflective film.
b) What is the purpose of each part? To allow for light to reflect.
8) Clearly explain what is meant by the term geometric optics.
a. Geometric optics is the study of the use of light rays to determine how light behaves when it strikes objects.
9) Classify each of these materials as transparent, translucent, or opaque: a textbook (opaque), frosted glass (translucent), a single sheet of thin tissue paper (translucent), a clean sheet of glass (transparent), a rock (opaque), clean air (transparent), apple juice (transparent or translucent), sunglasses (transparent).
10) What has historically been the main use for plane mirrors? To reflect images.
11) A basketball does not give off light. Explain with the aid of a ray diagram how you are able to see a basketball.
12) Explain why a piece of metal would make a better reflector than a piece of wood. The surface of a piece of metal is more likely to be smooth, leading to specular reflection. The surface of a piece of wood is more likely to be rough, leading to diffuse reflection. Both would absorb light.
13) Explain, with the help of ray diagrams, why the shadow created by your hand on a wall grows larger when you move your hand toward the light source.
14) Under what conditions can a transparent material become translucent or even opaque? A thin sheet of plastic is transparent. However, if several sheets of plastic are layered on top of one another they will become translucent due to the way that light will bend. If these sheets are increased in number, they may even become opaque.
15) A spotlight shines on an actor on a stage. Describe the type of shadow the actor is likely to cast. The further the spotlight is from the actor, the smaller (and fainter) the shadow will be.
LAWS OF REFLECTION AND PLANE MIRRORS
1) In your own words, clearly distinguish between the terms normal, angle of incidence, and angle of reflection.
a. Normal – Perpendicular line to a mirror surface
b. Angle of incidence – Angle between incident ray and normal
c. Angle of reflection – Angle between the reflected ray and normal
2) Using a diagram, distinguish between the incident ray, the reflected ray, and the normal.
3) Clearly state the two laws of reflection.
a. The angle of incidence equals the angle of reflection, i=r
b. The angle of incidence and angle of reflection are always measured from the normal and not from the surface of the object
4) a) What is the difference between specular reflection and diffuse reflection? Specular reflection is reflection of light from a smooth surface ; diffuse reflection is reflection of light from an irregular surface.
b) Provide some examples of both specular reflection and diffuse reflection other than those given. Specular: glass, wall, table; Diffuse: any rocky surface, grass
5) a) If you were painting the walls in your classroom, would you want the walls to exhibit specular or diffuse reflection? Explain.
b) Given your choice, should you use gloss or matte paint? Answers will vary.
6) a) What would be the angle of reflection for an angle of incidence of 32o? 32 degrees.
b) What would be the angle of incidence for an angle of reflection of 47o? 47 degrees.
c) What would the angle of reflection be if the incident ray was 40o from the reflecting mirror surface? 50 degrees.
7) Specular reflection and diffuse reflection are concepts that can be applied to every room that you have ever been in. Describe how these concepts can be applied to your kitchen, bathroom, and bedroom. Answers will vary.
8) Draw a ray diagram and locate the virtual image of each object:
CONCAVE MIRRORS
Concave Mirrors Worksheet*****
1) List examples of how concave mirrors might be used at your school.
a. Science experiments
b. entrances and hallways – to avoid bumping into others
2) Describe the difference between a real image and a virtual image.
a. Real image – formed when light rays actually meet at the image
b. Virtual image – an image formed in a location where light does not actually reach. Ie: reflection in a mirror
3) Use a diagram to locate the focus in a concave mirror. The focus is the midpoint of C and V:
4) In your own words, state the imaging rules for concave mirrors. Answers will vary.
5) You are looking at your image in a makeup or shaving mirror. Where is your head located with respect to the focus (F).
a. Images in these mirrors will be magnified and virtual, so it would have to be between V and F.
CONVEX MIRRORS
Convex mirrors worksheet *****
1) List examples of how convex mirrors might be used at your school.
a. Answers will vary.
2) Why will a diverging (convex) mirror never produce a real image? Include a diagram in your explanation.
a. The rays of light will always meet behind the mirror. As a result, the image will always be virtual.
3) What is the relationship between type and the attitude of an image?
a. Convex mirrors will always have an upright and virtual iamge.
4) a) Why are convex mirrors placed on sharp turns in parking garages?
a. To allow for traffic to be seen coming from opposing lanes.
4b) State other uses for convex mirrors. Cell phones
CURVED MIRROR CALCULATIONS
1) See notes 2) +, image in front of mirror; -, image behind mirror 3) 1.7 cm (inverted), 9.2 cm (real)
4) A focal length of 25 cm and distance of 30 cm will only yield an inverted image (-) 5) Real, + di, Virtual, -di
6) 0.7 m (virtual), 0.1 m (upright) 7) 0.5 m (virtual), 0.2 m (upright) 8) 0.2 m (virtual), 0.1 m (upright)
9) 0.7 m (virtual), 0.1 m (upright) 10) 38.7 cm (virtual), 12.1 cm (upright)
INDEX OF REFRACTION AND SNELL’S LAW
1) The speed of light in leaded glass is 1.66x108m/s. What is the index of refraction of this type of glass?
n = c/v
c =3.0 X 108 m/s
v = 1.66x108m/s
Therefore, n = 1.81
2) The speed of light in quartz is 2.1x108m/s. What is the index of refraction of quartz?
n= c/v ( c = 3.0 X 108 m/s ; v = 2.1x108m/s )
Therefore, n = 1.43
3) The speed of light through a material is 1.24x108m/s. What material is it? Diamond
4) What is the speed of light through ethyl alcohol?
n= 1.36
c = 3.0 X 108 m/s
v = ?
v = c/n
v = 3.0 X 108 m/s / 1.36
v = 2.20 X 10 8 m/s
Therefore, the speed of light is 2.20 X 10 8 m/s.
5) What is the speed of light through vegetable oil? 2.04 X 108 m/s
6) What is the speed of light through a diamond? 1.24 X 108 m/s
7) When light passes from air into water at an angle of 30o from the normal, what is the angle of refraction?
1.0 sin 30 = 1.33 sin R
Therefore, the angle of refraction is 22.1 degrees.
8) When light passes from water into a diamond at an angle of 45o from the normal, what is the angle of refraction?
1.33 sin 45 = 2.42 sin R
Therefore, the angle of refraction is 22.9 degrees.
9) The refractive index of the lens in a human eye s 1.41. If a ray of light goes from the air into the lens at an angle of 55.0o, what is the angle of refraction?
1.0 sin55 = 1.41 sin R
Therefore, the angle of refraction in 35.5 degrees.
10) A ray of light approaches a jar of honey at an angle of 30.0o. If the angle of refraction is 19.5o, what is the refractive index of honey?
1.0 sin 30 = n2 sin19.5
1.50 = n
Therefore, the refractive index for honey is 1.50.
11) A block of amber is placed in water and a laser beam travels from the water through the amber. The angle of incidence is 35o while the angle of refraction is 24o. What is the index of refraction of amber?
1.33 sin35 = n2 sin24
1.88 = n2
Therefore, the index of refraction is 1.88.
12) A red laser beam travels from Plexiglass into lemon oil. The angle of incidence is 40.0o and the angle of refraction is 44.4o. What is the refractive index of lemon oil?