Optics Review Package Answer Section TRUE/FALSE 1. T 2. F Reflection occurs when light bounces off a surface Refraction is the bending of light as it travels from one medium to another. 3. T 4. F 5. T 6. F Sunglasses can protect your eyes from harmful ultraviolet radiation. 7. F A translucent object allows some light to pass through it, but it scatters the light from its straight path. 8. F A normal is a line that is perpendicular to the reflected surface. 9. T 10. T 11. F A double convex lens is used in overhead projectors to make the rays of light converge. 12. F A concave lens causes rays of light to spread out or diverge. 13. F The diagram shows a concave lens, which is thinner and flatter in the middle than around the edges. 14. F The iris is the coloured ring that functions like the diaphragm of a camera. 15. F Snow blindness is a temporary condition that occurs in places where a person is overexposed to the glare of sunlight. 16. T 17. F Light in binoculars is reflected back and forth inside a short tube. 18. F Therefore, it is a reflecting telescope. 19. T 20. F Total internal reflection occurs in optical fibres and is the reflection of light off the wall of the fibre back into the fibre. MULTIPLE CHOICE 1. C 2. B 1
3. D 4. C 5. D 6. B 7. B 8. B 9. C 10. B 11. A 12. D 13. D 14. A 15. B 16. D 17. B 18. A 19. C 20. C 21. C 22. C 23. A 24. D 25. A 26. A 27. A 28. D 29. D 30. A 31. B 32. A 33. D 34. D 35. C 36. B 37. A 38. D 39. D 40. A 41. C 42. D 43. C 44. B 45. C 46. B 2
47. D 48. D 49. C 50. D COMPLETION 1. Refraction 2. prism 3. red 4. radiant 5. angle, incidence 6. normal 7. angle, reflection 8. plane 9. concave lens 10. far 11. retina 12. optic nerve 13. cone cells 14. refracting 15. reflecting 16. aperture 17. wavelength 18. convex 19. longer 20. diaphragm MATCHING 1. D 2. C 3. E 4. A 5. B 6. E 7. A 8. D 9. B 10. E 11. C 12. A 3
13. D 14. B 15. E 16. C 17. A 18. F 19. H 20. G SHORT ANSWER 1. There are no particles in a vacuum. Light slows down in the denser environment of Earth's atmosphere. This is the principle of refraction. 2. You see the colour of light reflected by the object. The colours you do not see are absorbed by the object. 3. Frequency is halved. The longer a wave is, the fewer times it vibrates per second. 4. Wavelength and frequency are inversely proportional. As wavelength decreases (becomes shorter), frequency increases. 5. The wave model helps to explain some of light's strange behaviours while accounting for the fact that light travels in straight lines. 6. In a transverse wave the matter in the medium moves perpendicular to the direction that the wave travels, while in a compression wave the matter in the medium moves back and forth along the same direction that the wave travels. 7. In a light wave, electrical and magnetic fields vibrate. As a result, light is classified as electromagnetic radiation. The electromagnetic spectrum classifies light into visible and invisible forms of radiant energy. Any five appropriate examples such as: - radio waves - infrared - ultraviolet - X-ray - gamma ray 8. Without the ozone layer, harmful ultraviolet radiation from the Sun would not be blocked and would continue into Earth's atmosphere. Ultraviolet radiation can cause skin cancer. This radiation can damage the cornea of the eye, causing slow loss of vision. 9. One of: - All energy in the electromagnetic spectrum is radiant energy. - All types travel in waves. - All types can travel in space (no medium). 10. The image looks twice as far away. 11. (a) any two of: mirror type, location of object, image characteristics (b) dependent variables image characteristics (e.g., size, attitude, location); independent variables mirror type or location of object (c) Repeat test with a different object. 12. Babies need to be very close to a mirror so they can focus. When at close range to a concave mirror, the baby's image will appear upright and larger. 4
13. Concave mirrors would make guests appear upside down and smaller if the guests are far away from the mirror. When they are close to the concave mirror, they would appear upright and larger. Convex mirrors would emphasize certain body parts (such as facial features), making your guests look comical. Combining concave and convex mirrors might shrink some parts of a person's body, while accentuating other parts. 14. Answers will vary, but should indicate that the mirror must be angled to reflect the overall scene. A convex mirror would reflect a larger area than a plane mirror. 15. Drivers looking into their rearview mirrors will see the backward printing on the vehicle behind them. The printing will appear reversed in the mirror, making it easier for the driver to read. 16. In regular reflection, all the normals related to light reflected from a smooth surface point in the same direction. The images created from regular reflections are clear. In random reflection, the normals related to light reflected from rough surfaces will point in random directions, depending on exactly where the incident rays strike the surface. When light reflects off a rough surface, random reflection occurs and no image results. 17. Convex lenses can be used to create a magnifying glass. If you place a flammable material (such as paper or bits of kindling wood) under your convex lens, the material will likely start to burn. Answers will vary, but may include any three of: - exercise extreme caution when dealing with open flames - keep your skin, hair, and clothing away from the flames - tie back long hair - build a ring of stones or use a metal pail to contain the fire - have dousing material nearby 18. At first you will not be able to see anything. After several moments, your eyes will adjust to the darkness. The iris reflex will allow the pupil to grow very large. More of the "star light" will enter your eyes, and you will be able to find your way to your seat. 19. The blind spot is the point where the optic nerve enters the retina. This area does not have any light-sensing cells. When light strikes the retina at this point, the retina neither detects light nor transmits the message to the brain. 20. Near-sighted people have trouble seeing distant objects. Objects that are near are more clearly in focus. Far-sighted people have trouble seeing objects that are close to them. Objects far away are more clearly in focus. 21. The two different types are refracting and reflecting. In a refracting telescope, light from a distant object is collected and focussed by a convex lens. A reflecting telescope uses a concave mirror to collect and focus rays of light from a distant object. 22. No. Yellow (a secondary colour) light is made from red and green light. Adding yellow to blue is then the same as adding the three primary colours, which produce white light. 23. 1. red, blue, green 2. red, cyan 3. blue, yellow 4. green, magenta 5
24. (i) crest (ii) rises (iii) trough (iv) wavelength (v) lowers 25. Wear light clothing that covers your arms and legs. Use a sunscreen lotion. Wear sunglasses. 26. convex lens 27. (a) distance from mirror, amount of store seen (b) amount of store seen (c) distance from mirror 28. A flashlight has a concave lens. Concave lenses cause the light to spread out. At night, the flashlight would light up the area in front of it and a little bit of the periphery as light is transmitted through the lens. 29. A car headlight has a concave lens. The light bulb is near the principal focus. As the light travels through the lens, it diverges or spreads out. Headlights are needed at night to light up a road. The intensity of the light can be regular or high beam. The high-beam option allows for greater visibility because more light spreads out farther. 30. The iris functions like the diaphragm of a camera. 31. i) Binoculars ii) a) convex lens; b) triangular prisms; c) eyepiece iii) Binoculars are actually two reflecting telescopes mounted side by side. The telescopes are shortened by the insertion of prisms. Prisms serve as plane mirrors reflecting light back and forth. 32. red, orange, yellow, green, blue, indigo, violet 33. (a) crest (b) trough (c) wavelength 34. 1 mark for explanation, 1 mark for each correct colour. The visible spectrum is sunlight refracted into different colours. (a) red (b) orange-red (c) orange (d) yellow (e) green (f) blue (g) indigo (h) violet 35. heat radiation 36. Radar is shorter wavelength microwaves and is used in tracking the movement of automobiles and aircraft. 37. The wave model of light pictures light travelling as a wave. The model predicts how light will behave. 6
38. The angle of reflection is equal to the angle of incidence. 39. The audience watches the shadows cast on the translucent screen (some light passes through). The opaque puppets do not let any light pass through. 40. - translucent surface (e.g., wax paper): Some light passes through, but the light is scattered from its straight path. - transparent surface (e.g., plastic wrap): All the light passes through. - opaque surface (e.g., wood): No light gets through. 41. Answers will vary; for each mirror, accept any one of: - concave: cosmetic mirror, telescope - convex: sideview mirror on a car, security devices PROBLEM 1. (a) No colour passes through the filter. Green and blue light combine to make cyan. Since the red filter allows only red light to pass through (absorbing the rest of the light colours) and the cyan light has no red component, it will not pass through. (b) All colours except red. 2. There are no particles in a vacuum. Light slows down in the denser environment of Earth's atmosphere. This is the principle of refraction. 3. (a) look for an "If then" formula; statements such as If blue light is shone onto a red tomato, then the tomato will appear blue are appropriate (b) variables include: colour of light, appearance of tomato or colour of tomato with light on it. 4. When light strikes an object, such as a green piece of paper, the light may be reflected off the object, absorbed by the object, or transmitted through the object. When white light is shone on green paper, the green paper absorbs all the colours of light except the green. Green light is reflected, making the paper appear green. 5. look for: the conversion rate 1 nm = 1.0 10-9 m, mechanics of calculation, correct answers. (a) 15 nm 10-9 = 0.000 000 015 m = 1.5 10-8 m (b) 50.0 nm 10-9 = 0.000 000 500 = 5.0 10-7 m (c) 0.05 nm 10-9 = 0.000 000 000 050 = 5.0 10-11 m 6. look for: use of conversion factor 1 nm = 1.0 10-9 m, mechanics of calculation, correct answers. (a) 100 nm 10-9 m = 0.000 000 1 = 1.0 10-7 (b) 2000 nm 10-9 m = 0.000 002 = 2.0 10-6 m 7
7. Gamma rays have the shortest frequency and the highest energy of all the radiant waves. Gamma rays result from nuclear reactions and can kill cells. X-rays easily pass through skin and muscle, but do not kill cells. 8. As light travels through the atmosphere, it is refracted by particles in the atmosphere. The light from the stars near the horizon must pass through more atmosphere and therefore is subject to more refraction. 9. Once the beam of light enters the oil, it travels more slowly, bending and refracting. The angle of incidence in water is greater than the angle of refraction in the oil. 10. (a) transparent (b) opaque (c) translucent 11. The shape of the pupil allows different amounts of light in, but will not affect focus. This is important for cats who hunt at night. 12. Should use an "If then" formula that must identify variables in a statement. Answers will vary. Example: If an object moves closer to the film, then the lens must move farther from the film to keep the image in focus. 13. Diagram should include the following: 14. You would use a wide-angle lens. These lenses have a shorter focal length that produce a relatively small image of the object, but have a wide field of view. 15. You would use a telephoto lens. These lenses have a longer focal length that make the images larger and seem closer than they actually are. 8
16. In the camera the focal length is adjusted by moving the lens system toward or away from the recording material. In the human eye the focal length is adjusted by the ciliary muscles changing the thickness of the lens. 17. Laser light is made up light of a single wavelength. When the laser light passed through the prism, it refracted. Different wavelengths of light refract at a different angles, but since there was only one wavelength, only one angle of refraction would be observed. 18. Light reflects off the flower (this is why we see it). The primary colours (red, green, and blue) strike the flower, but the green light is absorbed and the red and blue light combine to make the secondary colour, magenta (the colour of the flower we see). 19. (a) yellow (b) magenta (c) white (d) cyan 20. look for correct answer as well as the mechanics of the calculation. wavelength = 2 length of crest = 2 2.5 cm = 5 cm 21. look for correct answer as well mechanics of the calculation. 1 Hz = 1 vibration per second 600 vibrations = 10 vibrations/second = 10 Hz 60 s 22. look for correct answer as well as mechanics of the calculation 1 Hz = 1 vibration per second 880 vibrations = 220 vibrations/second = 220 Hz 4 s 23. - b - 40 - The angle of incidence is equal to the angle of reflection. 24. Mirages occur when air near the ground warms up, refracting the light from objects at a distance. This creates the illusion of a water surface, but it is really an image of the sky refracted onto the warm air near the ground. 25. Because the angle of incidence equals the angle of reflection (first law of reflection), you know that when you shoot the puck to bounce it off the boards, the angle at which you shoot it will be equal to the angle at which it will bounce off the boards. This knowledge will increase your accuracy when passing the puck. 26. The floor acts like a plane mirror. Because the angle of incidence equals the angle of reflection (first law of reflection), you can predict that the ball will bounce off the floor at the same angle (and in the opposite direction) as it approached the floor. 9
27. There are no particles in a vacuum. Light slows down in the denser environment of Earth's atmosphere. This is the principle of refraction. 28. It was a mirage. The air close to the ground is hotter and less dense than the air higher up. As a result, light from the sky directed at the ground is bent upward (refracted) as it enters the less dense air. What looked like water was actually an image of the sky refracted by the warm air near the ground. 29. Concave lenses would be best. In near-sightedness, the image falls short of the retina. Concave lenses will move the image back so it will form on the retina. 30. Convex lenses would be best. In far-sightedness, the image falls behind the retina. Convex lenses will move the image closer so it falls on the retina. 31. a) optic nerve b) retina c) lens d) iris e) pupil f) cornea 32. b) Retina: Light-sensitive area where the image is formed d) Iris: Opens or closes to let in more light e) Pupil: Actual opening that lets in light. 10