Download Unit 1 – Cells and Systems

Unit 2 – Optics
Chapter 4 –
Many properties of light can be understood using a wave model of light.
4.1 Properties of Waves
-wave: a disturbance of movement that transfers energy through matter or
space☇ ex: water waves, sound waves, microwaves
-energy: the capacity to apply a force over a distance
-force: push/pull on an object
amplitude
amplitude
*Features of a Wave*
-crest: highest point on a wave
-trough: lowest point on a wave
-wavelength: distance, in meters, for one complete cycle of the wave
☇ crest to crest; trough to trough
-amplitude: height of a wave crest or depth of a trough, as measured from
its rest position
-medium: matter in which a wave travels through
-some waves (ex: sound waves) can travel through space where
there is no medium
☇ two types of waves that travel through a medium are:
-Transverse Wave: matter in the medium moves perpendicular to
direction of wave
-Compression Wave: matter in the medium moves parallel to direction
of the wave
*Frequency*
-frequency: number of repetitive motions, or oscillations, that occur in a
given time
-usually measured in Hertz (Hz)
-when frequency of a wave increases, the wavelength decreases
-frequency = cycles/second; ex: hummingbird flaps wings 120times/3 sec; 40Hz
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4.2 Properties of Visible Light
-the wave model of light describes light as a wave that travels through
empty space
☇ model: verbal, mathematical, or visual representation of a scientific
structure or process, which allows scientists to construct and test
inferences and theories
-light energy is transferred from one location to another; from Sun to Earth
*Refraction of Light*
-refraction: bending or changing direction of a wave as it changes speed in
moving from one material to another
-light waves refract when they pass form one material to another
-longer wavelengths are refracted less than shorter wavelengths
-blue refracts more than red
*Colours of the Rainbow*
-white light is made up of waves of different wavelengths
-different wavelengths refract light by different amounts
-visible spectrum: band of colour when white light is separated into its
different colours
-seven most visible colours of spectrum: Red, Orange, Yellow, Green, Indigo,
violet (ROY G BIV)
*Producing the Visible Spectrum*
-a prism causes white light to split into a spectrum
-white light, such as sunlight, is the result of mixing together all t he
different colours
*Colour and Reflection*
-reflection: the visible effect when light strikes an object and bounces off
-when white light strikes object, some colours are reflected, some absorbed;
only reflected colours can be seen
-ex: yellow cloth reflects yellow and absorbs all other colours; shirt
appears black when there is no source of light
-three additive primary colours of light: red, green, blue (added together in
proper amounts makes white light)
-light of two additive primary colours will produce secondary colour
-three secondary colours: yellow, cyan, magenta
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4.3 Light and the Electromagnetic Spectrum
-radiant energy: energy, such as light, that travels by radiation
-in addition to visible energy/light, Sun also radiate invisible energy
-light we see is just tiny band of much broader spectrum of energy
*Electromagnetic Radiation*
-electromagnetic radiation: transmission of energy in the form of waves that
extend from the longest radio waves to shortest gamma rays
*Wavelengths Longer than Visible Light*
○Radio Waves
-radio wave: type of electromagnetic wave has longest wavelength and lowest
energy & frequency compared to all other types; used for communication
-used for: radio/television broadcasting; MRI technology to see inside body
○Microwaves
-microwave: type of radio wave that has shortest wavelength of radio waves
-used in: cooking food, telecommunications
○Radar
-radar: type of shorter-wavelength microwave
-used in: tracking motion of objects, weather forecasting, taking
images of Earth’s surface
○Infrared Waves
-infrared radiation: electromagnetic radiation that has a wavelength longer
than red end of visible spectrum but shorter than of radio waves; also – heat
-used in: remote controls, infrared cameras, CD-ROM readers
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*Wavelengths Shorter than Visible Light*
-wavelengths shorter than visible light have more energy than visible light
○Ultraviolet Waves
-ultraviolet radiation (UV): electromagnetic radiation that has a wavelength
shorter than that of the violet end of the visible spectrum but longer than
that of X rays
-just beyond visible region of spectrum
-posses much more energy than visible light
-UV rays striking skin allows body to make Vitamin D; overexposure can
cause sunburns and possible skin cancer
-used in: police (fluorescent powder to study fingerprints), kill bacteria in
food, water, medical supplies
○X Rays
-X rays: electromagnetic radiation having shorter wavelengths and higher
energy and frequency than ultraviolet rays
-used in: photographing teeth/bones; detect small cracks in metals;
photograph inside of machines; airport-examining luggage
○Gamma Rays
-gamma rays: electromagnetic radiation having the highest energy and
frequency and shortest wavelengths in the electromagnetic spectrum
-result from nuclear reactions
-used in: radiation therapy to kill cancer cells
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Chapter 5 – Optical systems make use of mirrors and lenses.
5.1 The Ray Model of Light
-light can be described as:
-particle model of light: a model that represents light as a stream of
fast-moving, tiny particles that travel in a straight line to the eye,
where they are absorbed to form an image
-ray model of light: a model that represents light as a straight line,
or ray, indicating the path of a beam of light
*Light and Matter*
-different materials can transmit, absorb, or reflect light
-transparent: allowing light to pass through freely, images are clearly seen
-translucent: allowing some light rays to pass through, but not enough to see
objects clearly
-opaque: absorbing or reflecting all light and not allowing any light to pass
through
*Shadows*
-shadow is created when an opaque object absorbs light rays
-shadows demonstrate that light travels in straight lines
-ray diagram shows how the distance from the light source affects the size
of the shadow an object makes
*Light Can Be Reflected*
-reflection is when light bounces off an object
-to act like a mirror, surface must be smooth
-incident ray: light ray that strikes a reflecting or refracting material
-reflected ray: light that is bounced back (reflected) from a reflecting
surface
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*The Law of Reflection*
-normal: an imaginary line drawn perpendicular to a reflecting or refracting
surface at the point where an incident ray strikes the surface
-angle of incidence: the angel formed by the incident ray and the normal
-angle of refection: the angle formed by the reflected ray and the normal
-law of reflection: angle of incidence equals the angle of reflection
*Light Can Be Refracted*
-angle of refraction: the angel of a ray of light emerging from the boundary
between two materials, measured between the refracted ray and the normal
-when light travels from one transparent medium to a transparent medium it
changes speed
-this change in speed causes the light to change direction
-bending of light due to change in speed = refraction
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*Refraction of Light in Water and Air*
-objects in water appear in a different location than they actually are; due
to the refraction of the light
-light refracts when it passes air at different temperatures
-mirage: a misleading appearance of illusion; can be result of
refraction of light through air layers of different densities
-ex: mirage is the light from sky bending as it approaches warm air
near ground
5.2 Using Mirrors to Form Images
-all mirrors reflect light according to the law of reflection
-plane mirror: flat, smooth mirror (mirror on wall, bathroom)
*Plane Mirrors*
-form an image that is upright and appears to be as far behind the mirror as
the object is in front of it
-rays reflect off mirror and back to bird’s eye; rays appear to be
coming from behind the mirror
-left/right appear to be reversed
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*Concave Mirrors*
-concave mirror: a reflective surface that curves inward and can magnify
objects
-focal point: the point at which converging light rays meet or from which
light rays diverge
-light reflecting off concave mirror converges
-converging: coming together at a point
-image formed by a concave mirror depends on location of
object:
-A) distant object
reflected: image is
small and upside down
-B) as object
approaches focal
point: image remains
inverted, but gets
larger
-C) object between focal point and
mirror: image appears larger than object
and is upright
-some uses: spotlights, flashlights, car
headlights, telescopes, make-up mirrors
-form an enlarged, upright image
of a person’s face so it is easier
to
see small details
*Convex Mirrors*
-convex mirror: a
reflective surface that
curves outward
-reflected rays diverge;
do not meet
-diverging:
spreading apart
-image formed by
convex mirror have two
characteristics:
-objects appear to be smaller than they are
-more objects can be seen in a convex mirror than
in a plane mirror
-some uses: security mirrors, rearview/side0view mirrors of automobiles
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5.3 Using Lenses to Form Images
-lens: a curved piece of transparent material that refracts light in such a
way as to converge or diverge parallel light rays; in the eye, the flexible
convex structure behind pupil and iris
-can be concave/convex
*Concave Lenses*
-concave lens: a lens that is thinner and flatter in the middle than around
the edges; refracts light rays so they spread out (diverge)
-produce images that are upright and smaller than the object
-sometimes used in eyeglasses and telescopes
*Convex Lenses*
-convex lens: a lens that is thicker in the middle than around the edges;
focuses light rays at a focal point (converge)
-used in: magnifying glasses
-focal length: distance from centre of the
lens to focal point
-images formed by convex lenses depends
on where object is relative to focal point
Distance of Object from Lens
more than two focal lengths
between one and two focal
lengths
object at focal point
less than one focal length
Type of Image Formed
smaller, inverted
larger, inverted
no image
larger upright
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Chapter 6 – Human
vision can be corrected and extended using optical systems.
6.1 Human Vision
-pupil: dark transparent region in centre of the eye where light enters
-iris: coloured circle of muscle surrounding pupil; controls the amount of
light entering the eye
-sclera: an opaque tissue surrounding the cornea; visible as the white part of
the eye surrounding the iris
-cornea: transparent tissue covering the iris and pupil
-made of cells that are transparent enough to let light pass through,
yet tough enough to hold eye together
-lens: flexible convex structure behind the pupil and iris
-retina: inner lining of back of eye containing light-sensitive rods and cones
that convert light images into electrical signals for interpretation by brain
-optic nerve: nerve that connects eye to brain; where electrical signals are
sent; area where optic nerve enters retina no light-sensing cells = blind spot
*The Cornea-Lens-Retina System*
-light rays pass through a focussing system involving the cornea, the lens,
and the spaces in eye filled with water fluid
-fluid between lens and cornea supports both cornea and lens, and
provides nutrients to cornea, which does not have any blood vessels
-fluid behind lens gives shape to eye and supports the lens
-light rays first entering eye are focussed and refracted by cornea so that
they converge toward retina
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-image that forms on retina is inverted; however, your brain interprets
image as being upright
*Black-and-White Vision and Colour Vision*
-the retina contains two types of light-sensitive cells called rods and cones
-rod cells: cylinder-shaped cells, located in retina, that absorbs light; they
allow us to see images in shades of light/dark when the light is dim
-cone cells: cone-shaped cells located in retina that absorb light; they allow
us to see colour in bright light
*Correcting Focus Problems*
[Normal Vision]
-when light rays from a distant object enters
eye, rays are nearly parallel
-convex lens causes rays to converge at retina,
producing a sharp image
-light rays from a nearby object are diverging
when they enter eye, so muscles in eye cause
lens to change shape, making lens thicker
[Near-Sighted Vision]
-near-sighted vision: a focussing problem in
which nearby objects are clear but distant
objects are blurred
-occurs because lens converges light rays to
form image in from of retina; by the time
light rays actually strike retina they spread
out again, causing person to see fuzzy image
-concave lens used to diverge parallel rays
slightly so image forms farther back, on
retina
[Far-sighted Vision]
-far-sighted vision: a focussing problem in
which distant objects are clear but nearby
objects are blurred
-light rays from distant objects are nearly
parallel; require less refraction to
converge than light from nearby objects
-however, light rays from nearby objects
are diverging as they enter eye
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-convex lens needed for light rays to come into focus exactly on retina
[Astigmatism]
-astigmatism: blurred vision caused by an
irregularly shaped cornea
Causes an image to focus on more than one
point on retina, resulting in blurred vision
-can be corrected using
eyeglasses/contact lenses/with laser
surgery to reshape cornea
*Blindness*
-blindness: any vision impairment that keeps people from carrying out
important life functions; ability to detect very little or no light
-in very rare cases, a blind person may not be able to detect any light
whatsoever; most people who are legally blind can perceive some light or
even have a limited amount of vision
-may be able to see a tiny part of the middle of the whole scene
(tunnel vision)
-may be able to only see the edges but not directly ahead
-maybe be able to see light/dark (not clearly), even with visual aids
*Other Types of Blindness*
-snow blindness: a painful condition of temporary partial or complete
blindness caused by overexposure to the glare of sunlight on snow
-treatment includes resting eyes in dark room for several days to
allow inflammation to decrease
-night blindness: a condition in which it is difficult or impossible to see in
dim light
-most common cause is rod cells losing ability to respond to light
-person might be born with night blindness, or it could develop due
to injury/malnutrition
-colour blindness: ability to see only in shades of grey
-usually considered a disability
-although colour blindness is rare, colour vision deficiency (inability
to distinguish certain colours) is quite common
-most common kind involves inability to tell red/green apart
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6.2 Extending Human Vision
-in order for the light rays passing through a lens to form a clear image, the
screen that is receiving the image must be correct distance from lens
-screen must be at place where all light rays from a given point on the object
converge
-if screen is placed too close to lens, light rays do not fully converge
by the time they strike the screen; imaged formed will appear blurred
-if screen is too far away, light rays converge and then begin to
diverge before they strike screen; blurred image
*Microscopes*
-compound light microscopes use two convex
lenses with relatively short focal lengths to
magnify small, close objects
-object to be viewed is placed on a
transparent slide and illuminated from
below
-light passes by/through object on slide and
then travels through objective lens
-objective lens = convex lens
*if distance from an object to a convex lens
is between one and two focal lengths, it
forms an enlarged image of object
-eyepiece lens also convex, then magnifies
image again
-final image can be hundreds times larger
than actual, depending on focal lengths of
the two lenses
-to focus image, object is moved closer to
or farther away from object lens
-adjusting distance to make image
clear is called focussing
*Telescopes*
-a telescope uses a lens or concave mirror that is much larger than your eye
to gather more of the light from distant objects
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-refracting telescope: a telescope that has a convex lens to collect and focus
light from a distant object, and a convex eyepiece lens to magnify the image;
the lenses bend the light to focus it
-problems include – large objective lenses
flex, due to own weight and
distort the image
-glass lenses, even highest quality,
absorbs some light; expensive
-reflecting telescope: a telescope that has a concave mirror, a plane mirror,
and convex lens to collect and focus light from distant objects
-light enters telescope, is focused
after reflecting off concave mirror
-plane mirror reflects light towards
eyepiece
-convex lens in eyepiece magnifies
image
*most large telescopes are reflecting
telescopes
*Binoculars*
-binoculars are actually two refracting
telescopes mounted side by side
-to shorten length of tubes in
binoculars, prisms are used to reflect
the light back and forth (serve as plane
mirrors)
*Cameras*
-light enters camera through opening called aperture
-light then passes through lens which focuses image on light detector
-cameras can have different types of lenses
-wide-angel lens allow for wide field of view
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-telephoto lenses allow distant object to appear larger
*Lasers*
-laser light: light that only has
one wavelength and in which all
light waves are moving in the
same direction and all the crests and troughs are lined up
-travels great distances without spreading out; contains lots of energy
-light does not refract into rainbow, as would happen with normal light
-lasers can be used in place of scalpels in surgery
-remove cataracts
-reattach retina
-laser eye surgery to reshape cornea
*Optical Fibres*
-optical fibre: a transparent glass fibre that transmits light from one place
to another, even around corners
-transmit light using total internal reflection
-total internal reflection: a type of reflection in which light strikes a
boundary between two materials and is completely reflected
-used for medical procedures (orthoscopic surgery), telecommunications
(telephone, internet, video)
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