Download Unit C: Light and Optical Systems

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 EnergyThermal EnergyVisible 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 lightEnergy absorbed by particlesVisible 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.
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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
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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
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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
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