1. investigate the nature of light and vision; and describe the role of invention, explanation and...
TRANSCRIPT
Unit C: Light and Optical Systems
1. Investigate the nature of light and vision; and describe the role of invention, explanation and inquiry in developing our current knowledgea) identify challenges in explaining the nature of light and visionb) 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
c) investigate light beams and optical devices, and identify phenomena that provide evidence of the nature of light
1.1 The Challenge of Light
In history, people were known to use light to their advantage, but they never really knew what light was.
Early Light Ideas (6th Century BC)
Pythagoras – mathematician thought that light consisted of beams that came from people’s eyes in straight lines. Sight occurred when beams of touch the objects a person was looking at. Problem: if this is true, we
would be able to see at night!
Still accepted for many years.
Early Light Ideas (6th Century BC)
Euclid Angle of light hitting a
flat mirror is the same as the angle of light reflected off the mirror.
Suggested light travels in straight lines.
Ptolemy Light beams bend
when they go from air to glass.
Middle Ages Light Ideas (1000 AD)
Al-Haytham – wrote a book on optics First to accurately describe
how the vision works. Showed that light bounces
off objects and then travels to the eye. (light doesn’t come from the eye but travels to the eye)
Pythagora’s theory was abandoned.
Middle Ages Light Ideas (1000 AD)
Newton – interested in rainbow colors. Using a prism, Newton showed
that white light is a mixture of different colors.
As light passes through the prism, it split into separate colors.
Michelson – placed mirrors between two mountains and measured the distance and the time it took to send of beam of light from one mirror to the other. Found the speed of light to be
299 798 kilometers/second.
Properties of Light
Light travels in straight lines.Light can be reflected.Light can bend.Light is a form of energy.
Questions pg. 181
Light Inquiry Lab
1.2 Optical Devices
Optical devices – any technology that uses light. Example: mirror, Hubble space
telescope, glasses Invention of optical devices has
improved daily.
Microscopes
Hans and Zacharias Jansen – built first microscope in 1595 (simple design)
Leeuwenhok – used a microscope to look a pond water, blood and plaque scrapped from teeth. Found “little animalcules” (actually bacteria, protozoa, algae, and red blood cells) Discovery of microscope lead to new science of
microbiology (study of micro-organisms) Microscope sees two lenses (one in eyepiece
and one in objectives) and the light to see images in greater detail.
Telescopes
First telescope made in 17th century in the Netherlands Telescopes both
magnify and collect light
Telescopes provide enlarged images of distant objects using lenses and mirrors.
Galileo
Built himself a telescope in one day and then started to improve his design
Discovered mountains and craters on the Moon, small objects circling Jupiter, and then Venus has phases like the Moon.
Types of Telescopes
Refracting telescopes – two lenses (one at each end of a long tube). Larger lens collects light and focuses rays towards eyepiece. Eyepiece allows you to see object larger than it appears without telescope
Types of Telescopes
Reflecting telescopes – uses a large circular mirror that curves inward. Curved surface gathers light well and another mirror inside the telescope directs light to eyepiece that leads to the eye.
Binoculars
Too short refracting telescopes fixed together are called binoculars.
Not as powerful as telescopes but more convenient.
Questions pg. 186
Unit C: Light and Optical Systems
1. Investigate the transmission of light, and describe its behaviour using a geometric ray modela) investigate how light is reflected, transmitted and absorbed by
different materials; and describe differences in the optical properties of various materials
b) measure and predict angles of reflectionc) investigate, measure and describe the refraction of light
through different materialsd) investigate materials used in optical technologies; and predict
the effects of changes in their design, alignment or composition
2.1 Light Travels in Rays and Interacts with Materials
Light travels in straight lines.
Ray Diagrams
Ray diagrams used to show how light travels. Light traveling from source is
shown as straight lines of the arrows.
Arrows indicate the direction of travel.
Ray diagrams don’t show all light rays, but are useful in explaining how light behaves in different situations.
Ray Diagrams
Example – diagrams can explain brightness (intensity) changes the distance. Fewer light rays hit your eyes as you move further away.
Ray Diagrams
Ray diagrams explain shadows: Light hits object so light rays cannot continue and
a shadow was formed.
Light Interacts with Materials
Light acts differently with different types of materials. Transparent materials – transmit
light (light can pass through them)▪ Example – glass, clear plastic
Translucent materials – allow some light (not all) to pass through them▪ Example – frosted window pane
Opaque materials – do not allow any light to pass through them (absorbs or reflects the light)▪ Shadow created behind these materials▪ Example – wood, metal, brick
Light Interacts with Materials
Non-luminous materials – don’t produce light. Light that gets to the eyes from the opaque object is reflected from a light source.
Luminous materials – produces light itself. Helps us to see all non-luminous materials around us.
Type of material
What happens when light strikes
Examples Ray diagram
Transparent All light is allowed to pass streaked through, transmitted.
Clear glass, clear plastic
Translucent Some light is allowed to pass through, some scattered.
Frosted glass, tissue paper, wax paper
Opaque No light passes through, reflected or absorbed.
Wood, desk, eraser
Types of Reflection
REGULAR REFLECTION Light hits a smooth surface
(incoming rays travel parallel to one another)
All rays are reflected at the same angle (look the same as though you hadn’t seen them as a reflection)
Produced clear image, but eyes must be in direct path of reflected rays to see image.
DIFFUSE REFLECTION
Light hits a rough/uneven surface
Each ray is reflected at a different angle
Reflected rays don’t remain parallel.
When light is scattered, you see the surface from any position.
Questions pg. 193
2.2 The Law of Reflection
Incident rays – incoming rayso Smooth surfaces allow incident rays to bounce off
surface in parallel beams. (regular reflection)o Example – water, mirrors, glass, polished metal
The Law of Reflection
Plain mirrors – flat mirrors with the clearest reflections When a ray of light hits a plane near at an angle, it
bounces off the mirror surface at exactly the same angle. Normal – line and perpendicular to mirror Angle of incidence – angle between the incidents
ray and the normal. Angle of reflection – angle between the reflected
ray and the normal. Angle of reflection = Angle of incidences
Questions pg. 196
2.3 Reflecting Light with Curved Mirrors
Concave Mirrors Surface curves inward (like a bowl, cave) Obey the law of reflection When the parallel rays hit a curved surface, each ray is
reflected in a different direction. Rays all head to the focal point (common point) Good at collecting light and bringing it to a single
point. Used in flashlights, headlights, cosmetic mirrors,
telescopes to direct as much light possible in a useful way.
Images Formed By Concave Mirror
When the object is outside of the focal point, the image appears upside down. The closer the image is to the focal point, the larger the image is.
When object is between the focal point and the mirror, the image appears enlarged and right side up.
Convex Mirrors
Mirror with surface curved outwards Opposite of concave mirror Spreads out light rays Image seems to originate from a smaller point
behind the mirror
Questions pg. 199
2.4 Transparent Substances Refract Light
Light bends when it leaves water, making objects seem in places that they are not Interface – boundary where two different
substances meet
How Light Refracts
Refraction – light bends when it travels at an angle from one medium (substance) to another.o Due to changes in speed of lighto Example - Light in a vacuum = 300 000 km/s (nothing slows
light down) When light strikes a medium of different density at an angle, it will
refract. If a new medium is very dense, the light will slow down
(more refraction) Example - Diamonds are more dense than water – high refraction
When the light slows down, the light bends towards the normal line.
Term Quiz
Questions pg. 203
2.5 Lenses Refract and Focus Light
Lenses collect and bend lightLens – piece of curved glass (or
transparent material) that refracts light in a predictable way
Types of Lenses
Concave lenses Thinner in the center then
at the edges Light refracted away
from the center of the lens (light diverges or spreads out)
Convex Lenses Thicker in middle than at
edges Light refracted towards
the center of the lens (light rays move toward each other)
Can be used as a light collector
Forms a real image (light rays meet at a point and can be projected on the screen)
Image is upside down
Image Formation with a Convex Lens
If the object is behind the focal point, it appears smaller and upside down.
If the object is between the focal point and the lens, it appears right side up and magnified.
Questions pg. 208
Unit C: Light and Optical Systems
1. Investigate and explain the science of image formation and vision, and interpret related technologiesa) demonstrate the formation of real images, using a double convex lens, and
predict the effects of changes in the lens position on the size and location of images
b) demonstrate and explain the use of microscopes; and describe, in general terms, the function of eyeglasses, binoculars and telescopes
c) explain how objects are seen by the eye, and compare eyes with cameras d) compare the function and design of the mammalian eye with that of other
vertebrates and invertebrates e) investigate and describe the development of new technologies to enhance
human visionf) investigate and interpret emerging technologies for storing and transmitting
images in digital form
4.1 Image Formation In The Eyes And Cameras
Eyes and cameras are image of producing technologies.
Eye CameraPupil – allows light into eye Aperture – allows light into
cameraIris – colored part of the eyes. Controls the size of the pupils and the amount of light entering the eye.
Diaphragm – changes the size of the aperture to allow the proper amount of light in for a picture.
Eyelid – open and closes to let a certain amount of light in
Shutter – open and close to let certain amount of light in. The longer it is open, the more light enters the camera.
Eye vs. Camera
Human Eye and Camera
In order to see, light rays strike the retina at the back of the eye. The retina contains photoreceptors (cells sensitive to light)o Two different types of photoreceptors:
Rods – sensitive to light (can function in low light) Cones – detect color (cannot function in low light)
When light hits the retina, photoreceptors are stimulated and send a message through the optic nerve to the brain.
Their brain makes sense of the message and translates it into an image.
Focusing the Light
Both eyes and cameras have transparent convex lenses that collect light and direct it to a focal point Lens must be the right shape to produce
a good image Muscles of the eye are used to shape the
lens to focus in on an object at different distances.
Image formed is upside down but the brain corrects this.
Correcting Vision
Farsightedness – cannot see close all objects clearly (image falls behind the retina)o Convex lens is prescribedo To converge light
Nearsightedness - cannot see far all objects clearly (image of falls in front of the retina)o Concave lenses are prescribedo To diverge light
Laser eye surgery can be used to fix vision defects. Surgeon uses a laser to reshape the cornea of eye. The new cornea acts as a corrective lens.http://
www.learnalberta.ca/content/tlfrbl/index.html?launch=true
Questions pg. 244
Write this in your notes.
The eye is considered a NATURAL technology.
The camera is considered an ARTIFICAL technology.
4.2 Other Eyes In The Animal Kingdom
Camera eyes – eyes that have a cornea, lens, and retina and are round in shapeo Most vertebrates (animals with
backbones) have the camera eyes.o Fish have camera eyes with a perfectly
round lens, which bulges out from the pupil, allowing it to see in practically every direction.
o Birds have sharper vision than humans because they have five types of cones (humans have only 3), each sensitive to different wavelengths of light.
Other Eyes In The Animal Kingdom
Nocturnal animals have eyes that collect as much light as possible because of their very large pupils.
They also have a layer, called tapetum lucidum, inside their eye, which acts as a mirror. They also have many more rods than cones in their retina making their eyes more sensitive to low levels of light.
Other Eyes In The Animal Kingdom
Compound eyes –eyes that are made of smaller units called ommatidium.o Most insects and crustaceans have
compound eyeso The compound eye is great for
spotting movement, due to their convex shape, but with so many lenses, it is difficult to form a single coherent image. Instead it forms a mosaic image (much like a TV screen).
Questions pg. 238
4.3 Image Storage and Transmission
Most information today is stored digitally (converted into numbers).
Digital Images
A digital image is a picture made up of smaller colored pieces called pixels (picture elements). Each small pixel is assigned a place and is
represented by a number. This long series of numbers can then be stored in the memory of a computer to be accessed at a later time.
Coloring A Digital Image
Once the individual pixels are in the correct order, each pixel is assigned a value, which corresponds to a specific color.
When the picture gets reassembled, the computer reads the value of each pixel and makes that pixel the correct color.
Digital Image Quality
The quality of the digital image depends on the size of the pixels. o If the pixel is large you will see the image as a
collection of small squares. o If the pixel is small you will not notice the squares.
The quality of the image is represented by its resolution. The more pixels there are in the image, the higher the resolution.
Capturing Digital Images
Scanners, digital video recorders, and digital cameras use a charge-coupled device (CCD) to capture the light. The CCD is a grid similar to graph paper.
As the light enters each grid square it creates a small electrical charge, which is then converted into digital information and stored on a hard drive, compact disk or digital tape.
Transmitting Digital Images
Digital images can be sent over vast distances, without having to be processed. A powerful computer can convert the digital information very quickly.
Digital imaging can also collect different parts of the electromagnetic spectrum, allowing infrared as well as visible images to be captured.
Questions pg. 244