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What is Light? Explained
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 !!!
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
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)
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
