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What is Light?What is Light?
 Light is a small part of the Electromagnetic Spectrum or a form of Electromagnetic
Radiation.
 Other parts of the Electromagnetic Spectrum include:
 Radio Waves, Microwaves (mostly used for radar)
 Infrared Radiation (we can feel some of this as heat)
 Ultra-Violet radiation, X-rays, Gamma Rays & Cosmic Rays
Properties of LightProperties of Light
 Light travels in straight lines
 Light travels VERY FAST – around 300,000
kilometres per second.
 At this speed it can go around the world 8
times in one second.
Laser
Luminous and non-luminous objectsLuminous and non-luminous objects
 Luminous objects  Reflectors
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
ReflectionReflection
 Reflection is the bouncing of light falling on a surface
 Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence Angle of
reflection
The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection
In other words, light gets reflected from a surface at ____ _____
angle it hits it.
The same !!!
Reflection off Curved surfacesReflection off Curved surfaces
Concave
(curved in)
 Focuses parallel beams
Convex
(curved out)
 Disperses parallel beams.
Using mirrorsUsing mirrors
 Two examples:
1) A periscope
2) A car headlight
ReferenceReference
 Homework book – 3.1
RefractionRefraction
 Refraction: is the bending of light as it moves from
one medium (material) to another.
 Refraction occurs because the
speed of light changes as the
density of the material changes.
 Light speeds up in less dense
material (bending away from the
normal) and slows down in more
dense materials (bending toward
the normal).
 Density is measured by refractive
index
 If light strikes the interface
between the materials along
the normal (at right angles),
then it does not change
direction.
Air
Glass
Refraction:Refraction:
From Less Dense to More DenseFrom Less Dense to More Dense
 Light bends toward the
Normal
 Example of this include
Light passing from :
 Air to Water
 Air to Glass
Normal
Air
Glass
Angle of Incidence (Ai)
Angle of Refraction (Ar)
Refraction:Refraction:
From Dense to Less DenseFrom Dense to Less Dense
 Light bends away from the Normal
 Example of this include Light
passing from :
 Water to Air
 Glass into Water
Air
Glass
Normal
Angle of Incidence (Ai)
Angle of Refraction (Ar)
Passing Through a Block of GlassPassing Through a Block of Glass
Air
Glass
Note: The path of the beam of light is
parallel entering and leaving the block
 Copy the diagram into
you notebook and
 Mark on it:
 The Normal
 Angle Of Incidence
 Angle of Refraction
 State which material
has the greater density
Material BMaterial A
SolutionsSolutions
 Copy the diagram into you notebook
and Mark on it:
 The Normal
 Angle Of Incidence
 Angle of Refraction
 State which material has the greater
density
 Material B, as the light bends toward
the normal passing from A into B
Material BMaterial A
Reference
 Science Dimensions 3
pp 74 - 78
Work
 Questions pp 78 -9
 4-7, 9-14, 17, 18, 24-27
 Homework book Act 3.2
 Read practical activities
pp 80-1
LensesLenses
Converging or
Convex Lens
Diverging or
Concave Lens
•A lens is a piece of glass that bends 2 rays so that they cross
and form an image
• There are two different types of lenses, a converging lens and
a diverging lens
Converging orConverging or ConvexConvex LensLens
 A converging lens is thicker in the
center
 Parallel rays go through it and
come out so they all converge at
one point (the focal point)
 Convex lens are found in
Magnifying glasses, Microscopes
(at least 2), Telescopes (at least 2),
Cameras and glasses used to
correct Long-sightedness.
Diverging orDiverging or ConcaveConcave LensLens
 A diverging lens is thinner in the center
 Parallel rays go through the lens and
diverged (spread). The beam after passing
through the lens appears to be emanating
from a point in front of the lens; the
distance from this point to the lens is also
known as the focal length
 Concave lens are used in a peep hole, such
as you'd find in the door of a hotel room and
to correct Short-sightedness.
Ray DiagramsRay Diagrams
Bending Light Through a PrismBending Light Through a Prism
 Each wavelength (colour) of light
travels through a material at its own
particular speed .
 For example, when white light
passes through a prism some
wavelengths of light bend more
because their refractive index is
higher, i.e. they travel slower
 This is what gives us the "Spectrum".
 The "red‘’ light travels slowest, and
"violet" travels fastest, so are bent
differently. All the other colours lie
in between.
 This most easily seem with a prism
were the light is bent twice in the
same direction.
RainbowsRainbows
 Rainbows occur because the
refraction of light in water
droplets.
Refraction and reflection in a raindrop,
producing a rainbow.
White light separates into different colours on
entering the raindrop and then further
separated on leaving.
SightSight
 In the back of the eye we have specialised receptor
cells that react to light
 Photoreceptors
The EyeThe Eye
 The Cornea, Pupil, Lens are all working to focus
light (and hence the image) on to the retina
 Retina
 Rods: black & white, night vision
 Cones: color, day vision
 Fovea: sharpest vision (concentration of cones)
Rods & ConesRods & Cones
Rods Do Not See Red!Rods Do Not See Red!
The light response of the rods peaks sharply in the blue;
they respond very little to red light.
The ship captain has red instrument lights. Since the rods
do not respond to red, the captain can gain full dark-
adapted vision with the rods with which to watch for
icebergs and other obstacles outside. It would be
undesirable to examine anything with white light even
for a moment, because the attainment of optimum
night-vision may take up to a half-hour. Red lights do
not spoil it.
Colour BlindnessColour Blindness
Light & ColourLight & Colour
 White light can be split up to make separate colours. These
colours can be added together again.
 The primary colours of light are red, blue and green:
Adding blue and red
makes magenta
(purple)
Adding blue and green
makes cyan (light blue)
Adding all three
makes white
again
Adding red and
green makes
yellow
Seeing ColourSeeing Colour
 The Primary colours correspond to the three kinds
of color-sensitive cones in our retinas.
 We see objects because of the light they reflect.
 The colour an object appears depends on the
colours of light it reflects.
For example, a red book only reflects red light
White
light Only red light is
reflected
Seeing Black & WhiteSeeing Black & White
Seeing White
 White objects reflects
all colors.
Seeing Black
 Black Objects absorb
all light (& Reflect
none)
Seeing Primary ColoursSeeing Primary Colours
 When we see Red, Blue or Green objects we are
seeing just a single wave length of light reflected.
•The object appears BLUE because RED and GREEN are absorbed, while
only the BLUE light is reflected.
•We see the color BLUE.
•The object appears RED because GREEN and BLUE are absorbed, while only
the RED light is reflected.
We see the color RED.
•The object appears GREEN because RED and BLUE are absorbed, while only
the GREEN light is reflected.
•We see the color GREEN.
Seeing secondary ColoursSeeing secondary Colours
 We see secondary colours when two wave lengths
of light are reflected while one is absorbed.
Using coloured lightUsing coloured light
 If we look at a coloured object in coloured light we see something
different. For example, consider the clothing below:
White
light
Shorts look blue
Shirt looks red
 In different colours of light this kit would look different:
Red
light
Shirt looks red
Shorts look black
Blue
light
Shirt looks black
Shorts look blue
Some further examples:
Object Colour of light
Colour object seems
to be
Red socks
Red Red
Blue Black
Green Black
Blue teddy
Red Black
Blue
Green
Green camel
Red
Blue
Green
Magenta book
Red
Blue
Green
Using filtersUsing filters
 Filters can be used to “block” out different colours of light:
Red Filter
Magenta
Filter
Investigating filtersInvestigating filters
Colour of filter Colours that could be “seen”
Red
Green
Blue
Cyan
Magenta
Yellow
Red
Magenta
White
Yellow
Blue Green
Cyan
Light

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Light

  • 1. What is Light?What is Light?  Light is a small part of the Electromagnetic Spectrum or a form of Electromagnetic Radiation.  Other parts of the Electromagnetic Spectrum include:  Radio Waves, Microwaves (mostly used for radar)  Infrared Radiation (we can feel some of this as heat)  Ultra-Violet radiation, X-rays, Gamma Rays & Cosmic Rays
  • 2. Properties of LightProperties of Light  Light travels in straight lines  Light travels VERY FAST – around 300,000 kilometres per second.  At this speed it can go around the world 8 times in one second. Laser
  • 3. Luminous and non-luminous objectsLuminous and non-luminous objects  Luminous objects  Reflectors A luminous object is one that produces light. A non-luminous object is one that reflects light.
  • 4. ReflectionReflection  Reflection is the bouncing of light falling on a surface  Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection
  • 5. The Law of ReflectionThe Law of Reflection Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!
  • 6. Reflection off Curved surfacesReflection off Curved surfaces Concave (curved in)  Focuses parallel beams Convex (curved out)  Disperses parallel beams.
  • 7. Using mirrorsUsing mirrors  Two examples: 1) A periscope 2) A car headlight
  • 9. RefractionRefraction  Refraction: is the bending of light as it moves from one medium (material) to another.
  • 10.  Refraction occurs because the speed of light changes as the density of the material changes.  Light speeds up in less dense material (bending away from the normal) and slows down in more dense materials (bending toward the normal).  Density is measured by refractive index
  • 11.  If light strikes the interface between the materials along the normal (at right angles), then it does not change direction. Air Glass
  • 12. Refraction:Refraction: From Less Dense to More DenseFrom Less Dense to More Dense  Light bends toward the Normal  Example of this include Light passing from :  Air to Water  Air to Glass Normal Air Glass Angle of Incidence (Ai) Angle of Refraction (Ar)
  • 13. Refraction:Refraction: From Dense to Less DenseFrom Dense to Less Dense  Light bends away from the Normal  Example of this include Light passing from :  Water to Air  Glass into Water Air Glass Normal Angle of Incidence (Ai) Angle of Refraction (Ar)
  • 14. Passing Through a Block of GlassPassing Through a Block of Glass Air Glass Note: The path of the beam of light is parallel entering and leaving the block
  • 15.  Copy the diagram into you notebook and  Mark on it:  The Normal  Angle Of Incidence  Angle of Refraction  State which material has the greater density Material BMaterial A
  • 16. SolutionsSolutions  Copy the diagram into you notebook and Mark on it:  The Normal  Angle Of Incidence  Angle of Refraction  State which material has the greater density  Material B, as the light bends toward the normal passing from A into B Material BMaterial A
  • 17. Reference  Science Dimensions 3 pp 74 - 78 Work  Questions pp 78 -9  4-7, 9-14, 17, 18, 24-27  Homework book Act 3.2  Read practical activities pp 80-1
  • 18. LensesLenses Converging or Convex Lens Diverging or Concave Lens •A lens is a piece of glass that bends 2 rays so that they cross and form an image • There are two different types of lenses, a converging lens and a diverging lens
  • 19. Converging orConverging or ConvexConvex LensLens  A converging lens is thicker in the center  Parallel rays go through it and come out so they all converge at one point (the focal point)  Convex lens are found in Magnifying glasses, Microscopes (at least 2), Telescopes (at least 2), Cameras and glasses used to correct Long-sightedness.
  • 20. Diverging orDiverging or ConcaveConcave LensLens  A diverging lens is thinner in the center  Parallel rays go through the lens and diverged (spread). The beam after passing through the lens appears to be emanating from a point in front of the lens; the distance from this point to the lens is also known as the focal length  Concave lens are used in a peep hole, such as you'd find in the door of a hotel room and to correct Short-sightedness.
  • 22. Bending Light Through a PrismBending Light Through a Prism  Each wavelength (colour) of light travels through a material at its own particular speed .  For example, when white light passes through a prism some wavelengths of light bend more because their refractive index is higher, i.e. they travel slower  This is what gives us the "Spectrum".  The "red‘’ light travels slowest, and "violet" travels fastest, so are bent differently. All the other colours lie in between.  This most easily seem with a prism were the light is bent twice in the same direction.
  • 23. RainbowsRainbows  Rainbows occur because the refraction of light in water droplets. Refraction and reflection in a raindrop, producing a rainbow. White light separates into different colours on entering the raindrop and then further separated on leaving.
  • 24. SightSight  In the back of the eye we have specialised receptor cells that react to light  Photoreceptors
  • 26.  The Cornea, Pupil, Lens are all working to focus light (and hence the image) on to the retina  Retina  Rods: black & white, night vision  Cones: color, day vision  Fovea: sharpest vision (concentration of cones)
  • 27. Rods & ConesRods & Cones
  • 28.
  • 29. Rods Do Not See Red!Rods Do Not See Red! The light response of the rods peaks sharply in the blue; they respond very little to red light. The ship captain has red instrument lights. Since the rods do not respond to red, the captain can gain full dark- adapted vision with the rods with which to watch for icebergs and other obstacles outside. It would be undesirable to examine anything with white light even for a moment, because the attainment of optimum night-vision may take up to a half-hour. Red lights do not spoil it.
  • 31. Light & ColourLight & Colour  White light can be split up to make separate colours. These colours can be added together again.  The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow
  • 32. Seeing ColourSeeing Colour  The Primary colours correspond to the three kinds of color-sensitive cones in our retinas.  We see objects because of the light they reflect.  The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light White light Only red light is reflected
  • 33. Seeing Black & WhiteSeeing Black & White Seeing White  White objects reflects all colors. Seeing Black  Black Objects absorb all light (& Reflect none)
  • 34. Seeing Primary ColoursSeeing Primary Colours  When we see Red, Blue or Green objects we are seeing just a single wave length of light reflected. •The object appears BLUE because RED and GREEN are absorbed, while only the BLUE light is reflected. •We see the color BLUE. •The object appears RED because GREEN and BLUE are absorbed, while only the RED light is reflected. We see the color RED. •The object appears GREEN because RED and BLUE are absorbed, while only the GREEN light is reflected. •We see the color GREEN.
  • 35. Seeing secondary ColoursSeeing secondary Colours  We see secondary colours when two wave lengths of light are reflected while one is absorbed.
  • 36. Using coloured lightUsing coloured light  If we look at a coloured object in coloured light we see something different. For example, consider the clothing below: White light Shorts look blue Shirt looks red
  • 37.  In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue
  • 38. Some further examples: Object Colour of light Colour object seems to be Red socks Red Red Blue Black Green Black Blue teddy Red Black Blue Green Green camel Red Blue Green Magenta book Red Blue Green
  • 39. Using filtersUsing filters  Filters can be used to “block” out different colours of light: Red Filter Magenta Filter
  • 40. Investigating filtersInvestigating filters Colour of filter Colours that could be “seen” Red Green Blue Cyan Magenta Yellow