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Unit C: Light and Optical Systems STS and Knowledge 1. investigate the nature of light and vision; and describe the role of invention, explanation and inquiry in developing our current knowledge SF pp SF pp Identify challenges in explaining the nature of light and vision (e.g. recognize that past 176 - 183 explanations of vision involved conflicting ideas about the interaction of eyes and objects viewed; identify challenges in explaining upside-down images, rainbows and mirages) What Is Light? Light: is a form of energy that you can see The sun is a natural light source. Light bulbs are an example of an artificial light source Radiates: to send out energy in the form of waves or rays. Light can be produced by converting different kinds of energy- electric, chemical, fusion, heat etc. Light energy can also be transformed to different types of energy. Incandescent Sources An object can be heated to such a high temperature that it emits visible light, Incandescent source. The change happens as follows: Electrical EnergyThermal EnergyVisible Light Energy Incandescent lights give off about 95% of the energy as heat and the other 5% as light. Fluorescent Sources Materials absorb high-energy ultraviolet light and later emit some of this energy known as fluorescence. The change happens as follows: Ultraviolet lightEnergy absorbed by particlesVisible light energy This is the same process that takes place in a fluorescent bulb. See Figure 3.6 on pg 181 The advantage over incandescent lights is less energy is wasted as heated. However they are harder to produce. Phosphorescent Sources Differs from fluorescence because it continues to emit light even after the energy source has been taken away. Chemiluminescent Sources: light can also be released by chemical reactions e.g. Glow sticks. Bioluminescent Sources: Living creatures that produce their own light through chemical energy within your bodies. Luminous: objects that emit light. Non-luminous: do not emit light. SF pp 221226 Investigate the development of microscopes, telescopes and other optical devices; and describe how these developments contributed to the study of light and other areas of science Telescopes: help us to see distant objects Two main types of telescopes: Refracting: uses an eyepiece and objective lens (viewed straight on) Reflecting: uses an eyepiece and objective mirror (viewed through the side) Binoculars: two reflecting telescopes mounted side by side, prisms reflect the light to the eyepiece. Page 1 of 4 SF pp 184185, 237-245 Investigate light beams and optical devices, and identify phenomena that provide evidence of the nature of light (e.g. evidence provided by viewing the passage of light through dusty air or cloudy water) Is light a particle or a wave? Yes The Ray Model of Light Ray: a straight line that represents the path of a beam of light. Transparent: Allowing light to pass through e.g. Water, air, and glass. Translucent: materials that allow some light to pass through, the light is scattered from its straight path. E.g. Some types of glass and plastic. Opaque: a material that totally blocks light Waves consist of crests and troughs Crest: the peak or high part Trough: the bottom or low point Wavelength: the distance from crest to crest or trough to trough. Amplitude: the height of the crest or the depth of the trough Frequency: the number of cycles completed by a vibrating object per unit of time. Usually measured in Hertz (Hz) 2. Investigate the transmission of light, and describe its behaviour using a geometric ray model SF pp 188Investigate how light is reflected, transmitted and absorbed by different materials; and 199, pp 205 describe differences in the optical properties of various materials (e.g., compare light absorption of different materials; identify materials that transmit light; distinguish between clear and translucent materials; identify materials that will reflect a beam of light as a coherent beam) What happens when light strikes a surface? Type of behaviour What happens to light? Absorption Changes into some other kind of energy Reflection Bounces off the surface and travels in a new direction Refraction Travels through the surface, often in a new direction Nature of surface What else happens? Rough, dark, opaque surfaces Smooth, shiny surface Some light is usually reflected Some light is usually absorbed Different, transparent medium Some light is usually reflected Reflection: a process by which light strikes a surface and bounces back off that surface. Incidents Ray: The ray that comes from the light source and strikes the surface. Reflected Ray: The ray that bounces off the surface. Normal Line: When a ray strikes the surface perpendicular (at a 90 degree angle) Angle of Incidence: the angle between the incidence ray and the normal line Angle of Reflection: the angle between the normal line and the reflected ray. Law of Reflection: the angle of incidence equals the angle of reflection. Convex: mirror bulges outward – like a party balloon Concave: curved inward - like a bowl Page 2 of 4 SF pp 190193 Measure and predict angles of reflection SF pp 200206 Investigate, measure and describe the refraction of light through different materials (e.g., measure differences in light refraction through pure water, salt water, and different oils) Ray diagrams – “Inferring the law of reflection” and/or “When light reflects” Refraction: the bending of light when it travels from one medium to another. Angle of refraction: the angle between the normal and the refracted ray. *Light travels slower in more dense material! When light travels from one medium into a denser one, it will bend TOWARD the normal. When light travels from one medium into a less dense one, it will bend AWAY from the normal. Investigate materials used in optical technologies; and predict the effects of changes in their design, alignment or composition 3. Investigate and explain the science of image formation and vision, and interpret related technologies SF pp 208Demonstrate the formation of real images, using a double convex lens, and predict the effects 209 of changes in the lens position on the size and location of images (e.g., demonstrate a method to produce a magnified or reduced image by altering the placement of one or more lenses) Concave Lens: causes the refracting rays to spread apart. Convex Lens: causes the refracting rays to come together. SF pp 210 Demonstrate and explain the use of microscopes; and describe, in general terms, the function of eyeglasses, binoculars and telescopes Far-sighted eyeglasses: convex lenses (see Fig 3.32 B) Near-sighted eyeglasses: concave lenses (see Fig 3.32 C) SF pp 208218, 228-236 Explain how objects are seen by the eye, and compare eyes with cameras (e.g., compare focusing mechanisms; compare the automatic functions of the eye with functions in an automatic camera) Focusing The lens of the human eye is a convex lens. Focus: bringing light rays to a point. Near sighted: means that you have trouble seeing distant objects. Farsighted: the opposite of near sighted Accommodation: the process of changing the shape of the lens to adjust for different object differences The shortest distance at which an object is in focus is called the near point (In humans 25cm away, babies 7 cm) The longest distance is the far point, which is said to be infinity. Camera Part Film Diaphragm Lens Focusing ring Shutter Eye part Retina Iris Lens Ciliary muscle Eyelid Page 3 of 4 Diaphragm: controls the amount of light that gets in by controlling the size of the aperture (opening) Shutter: controls how much light enters by staying open a long or short amount of time. Retina: A light sensitive area at the back of the eye. Iris: in the human eye is the colored ring that functions like a diaphragm. Pupil: size of the opening that is controlled by the iris. (Dark part of the eye) Iris Reflex: the iris adjust the size of your pupil to meet the extreme dark or light, very rapid (try this in the bathroom mirror) Optic nerve: sends information about what is seen by the eye to the brain. Blind Spot: at the point where the optic nerve attaches to the retina does not have any light sensing cells therefore you can’t see that area. SF pp 219 Compare the function and design of the mammalian eye with that of other vertebrates and invertebrates (e.g. amphibians; fish; squid; shellfish; insects, such as the housefly) Research presentations! SF pp 246247, 249-256 Investigate and describe the development o new technologies to enhance human vision (e.g., laser surgery on eyes, development of technologies to extend night vision). Investigate and interpret emerging technologies for storing and transmitting images in digital form (e.g., digital cameras, infrared imaging, remote imaging technologies) Beyond Light Visible light and all other invisible forms of electromagnetic energy exist on the electromagnetic spectrum. Know figure 3.62 on page 249 Infrared radiation: heat radiation, anything that emits more heat than its surroundings. (Used on cops) Night vision scopes: infrared radiation can be converted into a visible iamge! Radio waves: have a longer wavelength than infrared and there are many kinds. E.g. Microwaves Ultraviolet radiation: (UV) very energetic radiation, causes damage to skin and eyes. Increased problem as a result of depletion of the Ozone layer. X rays- pass through tissues like skin and muscle but are absorbed by bone Gamma Rays- has the ability to destroy cells, can be used in cancer treatment. “Sharks with Laser beams attached to their heads” Laser: light amplification by the stimulated emission of radiation Incoherent light: crests from one wave might interrupt a trough from another jumbling them up. (Incandescent light bulb) Coherent: light emits waves with only one frequency and wavelength causing them to work together (laser) Many uses include: -Eye surgery -Scanning merchandise at a store -Laser guided missiles -Playing CD’s Page 4 of 4