Transcript Waves - Swinton Community School

KS4 Waves: Total Internal Reflection
and Communication
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Total Internal Reflection
Angle r
Angle i
Refracted
ray
Angle r
Refraction or
Reflection?
15
30
45
Angle r
Angle i
Incident
ray
Reflected
ray
60
75
At what angle of incidence did the ray change from
refraction to reflection? It depends upon the material you used.
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Simulation of a ray of light passing through
a semi-circular glass block
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Total Internal Reflection
This angle is called the critical angle [ c]
i<c
i=c
Refraction
Critical case
i>c
Total Internal
Different materials have different critical angles. Reflection
Diamond has the lowest at 24º which is why it
[TIR]
reflects so much light.
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The Critical Angle
How does refractive index affect the critical angle?
Research the missing values below and then
make a conclusion…
Material
Refractive
index
Critical
angle
Glass
1.5
42°
Water
1.33
49°
Diamond
2.4
24°
The greater the refractive index the smaller the
critical angle.
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Total Internal Reflection
Optical
Whatfibres,
are the
that are used in
communication,
applications ofuse
total
total
internal
internal
reflection.
reflection?
You
could
asked
A beam
ofbe
light
to
drawthe
on optical
the path
enters
of
the beam in an
fibre….
exam.
…NOTE how it is
refracted as it
enters the fibre…
…it travels down the
fibre through repeated
total internal reflections.
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Optical versus electrical
Research why communications systems now use
optical fibres instead of copper wires, use the table
below to help you.
Optical
Electrical
Information
Carry more
Attenuation
Less
More
Interference
No
Yes
Cost
More
Less
How is attenuation
solved in optical and
electrical fibres?
Carry less
Regenerators for electrical cables
Repeaters for optical fibres
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Digital and analogue
What is the difference between a digital
signal and an analogue signal?
What could they look like graphically?
Digital signals can only
be in one of two states,
e.g. 0 or 1.
Analogue signals are a
continuously changing
variable.
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Digital compared to Analogue
ADVANTAGES
DISADVANTAGES
 Signals are clearer less
susceptible to noise.
 Digital hardware is
expensive at the moment.
 Can be used quickly by
computers.
 Although digital signals
are unaffected by
electrical interference,
they don’t give a complete
signal [just lots of samples]
- some people feel that
analogue vinyl records
sound better than digital
CDs for this reason.
 Carry digital signals using
electromagnetic waves which
travel at the speed of light.
 Carry much more
information.
 Digital hardware is much
smaller.
 Easier to send over long
distances.
Electrical
storms
and
Noise
Which
is
signal
any
unwanted
is
most
Which
signal
carries
the
Analogue
Examples
Digital
What
of
is
noise
noise?
are?
random
thermal
noise.
information.
to noise?
mostprone
information?
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Communication systems
Communication systems include the same basic components.
You need to be able to define/describe the following:
Modulator
Encoder
Transducer
Transmitter
Amplifier
Storage
Decoder
Receiver
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Definitions
Component
Function
Encoder
Changes information into readable form
Decoder
Changes information to original form
Modulator
Allows wave to carry impulses AM/FM
Transmitter
Makes oscillations
Receiver
Collects information
Storage
Stores information e.g. CD, DVD, tape
Changes information into electrical form or
the other way round (microphone,
speaker)
Transducer
Amplifier
Increases intensity of received waves
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AM and FM
What do AM and FM stand for?
AM – amplitude modulation, where
the sound wave is communicated by
altering (modulating) the
AMPLITUDE of the radio wave
FM – frequency modulation, where
the sound wave is communicated
by altering (modulating) the
FREQUENCY of the radio wave
How do they compare?
More noise
Easier to send
Less noise
Travels further
Harder to send
Travels shorter
distances
AM
FM
More noise
Less noise
Travels further
Easier to send
Travels shorter
distances
Harder to send
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Storage and retrieval of information
What methods of storing information do you
know?
1.
2.
3.
4.
Magnetic Tape
_________________
Analogue
Digital
Video Disc - DVD Digital
_________________
Vinyl Records
_________________
Compact Disc - CD
_________________
Analogue
Digital
Which are digital and which are analogue?
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Which of the following is not a use of total
internal reflection?
A. Periscopes
B. Endoscopes
C. Fibre optic communication
D. Mirrors

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What does attenuation mean?
A. Strengthening
B. Increasing
C. Larger
D. Weakening

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Which of the following is not a a digital
storage method?
A. DVD
B. CD
C. CD-ROM
D. Vinyl record

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