### Unit 2 Optics

```Unit 2 Optics concept map
Sc.8 Unit 2 Optics
Unit 2 Optics
Ch.4 Properties of light waves
4.1 Waves
Wavelength
Frequency
Amplitude
Crest / Trough
4.2 Visible light
Roygbiv
Color
Refraction
Reflection
Ch.5 Mirrors and Lenses
4.3 E-M Spectrum
Visible
UV, Xray, Gamma
Transparent
Translucent
Opaque
Ch.6 Eye and Optical instruments
Law of reflection
Angle of incidence
Angle of reflection
Normal
Law of refraction
Angle of refraction
Normal
Mirage
Convex
Concave
Flat mirrors
Im ages Formed
Concave
Convex
Im ages formed
Uses
Parts of the eye
Near-sighted
Far-Sighted
Blindness
Optical instruments
Microscopes
Telescopes
Lasers and fiber optics
Light and Optics
Topics in this unit:
1) Properties of waves
2) Properties of light and the electro-magnetic
sprectrum
3) Colours
4) Refraction & Reflection
5) Human vision and eye defects
6) Optical instruments
4.1 Properties of waves
Waves transfer energy
Characteristics of waves:
Amplitude
Crest
Trough
Frequency
Sound waves
We hear things when they vibrate.
If something vibrates with a high frequency (vibrates very
quickly) we say it has a _____ pitch.
If something vibrates with a low frequency (vibrates
______) we say it has a ____ pitch.
Words – slowly, low, high, quickly
Drawing sounds…
This sound wave has a
_____ frequency:
This sound wave has a
___ _frequency:
Drawing sounds…
This sound wave has a
_____ amplitude
(loud):
This sound wave has a
_____ amplitude
(quiet):
4.1 Types of waves
Two types of waves:
Transverse
Compression
4.2 – Properties of Light
Light travels in straight lines:
Laser
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.
Colour
White light is not a single colour; it is made
up of a mixture of the seven colours of the
rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is “split up”
by raindrops.
The colours of the rainbow:
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Rainbows
Water drops act
like tiny prisms
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:
makes magenta
(purple)
and green
makes yellow
green makes cyan
(light blue)
three makes
white again
We see things because they
reflect light into our eyes:
Homework
Seeing colour
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
A pair of purple trousers would reflect purple light
(and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light
4.2 Properties of Light
summary
1) Light travels in straight lines
2) Light travels much faster than sound
3) We see things because they reflect light
into our eyes
4) Shadows are formed when light is blocked
by an object
4.3 Light and the ElectroMagnetic Spectrum
Electro-magnetic energy uses
telecommunications.
Infrared: heat
Visible: we can see
Ultra-violet: tanning,
cancer, fluorescent light
X-rays: medicine, dental
Gamma: cancer therapy
5.1 Light and Matter
Transparent: lets light
through freely, ex. glass
Translucent: most light
gets through; some is
scattered, images are
blurry, ex. Frosted glass
Opaque: no light gets
through
Shadows are places where light is “blocked”:
Rays of light
5.1 - Reflection
Reflection from a mirror:
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
The Law of Reflection
Angle of incidence = Angle of reflection
In other words, light gets reflected from a surface at
____ _____ angle it hits it.
The
same !!!
Clear vs. Diffuse Reflection
Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
Using mirrors
Two examples:
1) A periscope
Refraction
Refraction is when waves speed
up or slow down due to travelling
in mediums with different
densities.
In this case the light rays speed
up in the air and are bent,
causing the fish’s position to
change. The two mediums in this
example are air and water.
Law of refraction
When light moves from a more
dense medium (water) to a
less dense medium (air) it
speeds up - away from normal
When light moves from a less
dense medium (air) to a more
dense medium (water) it slows
down -toward the normal
Refraction can explain a mirage.
The mirage
is really the
sky
appearing
to be
sitting on
5.2 Images formed by
mirrors
Flat mirrors form images
that are:
-upright
-same size as object
-Equal distance behind
mirror; where the light
rays appear to meet
5.2 Concave mirrors
The image depends on
where the object is
placed.
Used in flashlights,
shaving mirrors,
telescopes
5.2 Convex Mirrors
Convex mirror images are
upright and smaller than
the object.
Used as security mirrors
and rear-view mirrors.
5.2 Concave lens-Diverges light.
Thinner in the middle.
Convex lens - focus light
Image depends on where the
object is compared to the
focal length.
Upside down, smaller
Upside down, larger
Upright, larger
6.1 The Eye
6.1 The eye
The eye has a number of
structures that refract
and focus images on the
retina including:
Cornea
Lens
Aqueous humor
Vitreous humor
6.1 Correcting focus problems
Near-sighted: long eyeball
Corrected with: concave
lens
Far-sighted: short eyeball
Corrected with: convex lens
6.1 Correcting focus problems
Astigmatism
Cornea is distorted
Laser surgery to
reshape the cornea
can correct it.
Laser eye surgery
6.1 Blindness
Causes:
Damaged cornea, lens,
retina
Disease: Cataracts,
glaucoma
Snow blindness
Color blindness
6.2 Extending vision
Optical instruments can
help us see very small
objects - nearby
Ex. Microscopes
Or
Objects very far away.
Ex. Telescopes
Using lenses & Mirrors
6.2 Eye vs Camera
Camera - eye
Ccd - retina
Lens - lens
Shutter - eyelid
Diaphragm - iris
Focussing ring - muscle
6.2 Lasers
Light Amplification by Stimulated Emission of Radiation
6.2 Fiber Optics
Transparent glass fibers
that transmit light using
Total Internal
Reflection.
Used for medicine, and
transmitting telephone,
video and internet
signals.
```