Download Waves - Total Internal Reflection and Communication

KS4 Physics
Total Internal Reflection
and Communication
1 of 20
21
© Boardworks Ltd 2005
2004
Contents
Total Internal Reflection and
Communication
Total internal reflection
Digital and analogue
Communication systems
Storage and retrieval of information
Summary activities
1
2 of 20
21
© Boardworks Ltd 2005
2004
Total internal reflection
Angle r Refracted
ray
Angle i Angle Refraction or
r
reflection
15°
30°
45°
Angle r
Angle i
Incident
ray
60°
75°
Reflected
ray
At what angle of incidence did the ray change from refraction
to reflection? It depends on the material used.
1
3 of 20
21
© Boardworks Ltd 2005
2004
Light ray simulation
1
4 of 20
21
© Boardworks Ltd 2005
2004
Total internal reflection
This angle is called the critical angle ( c).
i<c
i=c
Refraction
Critical case
i>c
Total internal
reflection (TIR)
Different materials have different critical angles.
Diamond has the lowest at 24°, which is why it reflects
so much light.
1
5 of 20
21
© Boardworks Ltd 2005
2004
The critical angle
How does the 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.
1
6 of 20
21
© Boardworks Ltd 2005
2004
Total internal reflection
What are the applications of total internal reflection (TIR)?
Optical fibres, used in
communication, use TIR.
You could be asked to
draw on the path of the
beam in an exam.
1. A beam of light enters
the optical fibre.
2. It is refracted as it
enters the fibre.
3. It travels down the fibre through repeated TIRs.
1
7 of 20
21
© Boardworks Ltd 2005
2004
Optical vs. electrical
Research why communications systems now use
optical fibres instead of copper wires.
Optical
Electrical
Information
Carry more
Carry less
Attenuation
Less
More
Interference
No
Yes
Cost
More
Less
How is attenuation
solved in optical and
electrical fibres?
1
8 of 20
21
Regenerators for electrical cables
Repeaters for optical fibres
© Boardworks Ltd 2005
2004
Contents
Total Internal Reflection and
Communication
Total internal reflection
Digital and analogue
Communication systems
Storage and retrieval of information
Summary activities
1
9 of 20
21
© Boardworks Ltd 2005
2004
Digital and Analogue
What is the difference between a digital signal and an
analogue signal?
Digital signals can only
be in one of two states:
0 or 1.
Analogue signals are a
continuously changing
variable.
What do they look like graphically?
1
10ofof20
21
© Boardworks Ltd 2005
2004
Digital vs. analogue
Advantages of digital
Disadvantages
 Signals are clearer and 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.
1
11ofof20
21
Electrical
storms
andthe
Noise
Whichsignal
issignal
any
unwanted
is
most
Which
carries
Analogue
Examples
What
Digital
is
ofnoise?
noise
are?
random
thermal
noise.
prone
information.
to
noise?
most information?
© Boardworks Ltd 2005
2004
Contents
Total Internal Reflection and
Communication
Total internal reflection
Digital and analogue
Communication systems
Storage and retrieval of information
Summary activities
1
12ofof20
21
© Boardworks Ltd 2005
2004
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
1
13ofof20
21
© Boardworks Ltd 2005
2004
Glossary
 amplifier – Increases intensity of received waves.
 decoder – Changes information to original form.
 encoder – Changes information into readable form.
 modulator – Allows wave to carry impulses AM/FM.
 receiver – Collects information.
 storage – Stores information (e.g. CD, DVD, tape).
 transmitter – Makes oscillations.
 transducer – Changes information into electrical form or
the other way round (e.g. microphone, speaker).
1
14ofof20
21
© Boardworks Ltd 2005
2004
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
1
15ofof20
21
AM
FM
More noise
Less noise
Travels further
Easier to send
Travels shorter
distances
Harder to send
© Boardworks Ltd 2005
2004
Contents
Total Internal Reflection and
Communication
Total internal reflection
Digital and analogue
Communication systems
Storage and retrieval of information
Summary activities
1
16ofof20
21
© Boardworks Ltd 2005
2004
Storage and retrieval of information
What methods of storing audio and video information
can you name?
1.
2.
3.
4.
Magnetic tape
_________________
Analogue
Digital
video disc - DVD Digital
_________________
Vinyl records
Analogue
_________________
Compact disc - CD
Digital
_________________
Which are digital and which are analogue?
1
17ofof20
21
© Boardworks Ltd 2005
2004
Contents
Total Internal Reflection and
Communication
Total internal reflection
Digital and analogue
Communication systems
Storage and retrieval of information
Summary activities
1
18ofof20
21
© Boardworks Ltd 2005
2004
Glossary
 amplifier – A device that boosts the strength of a signal.
 analogue signal – A signal that is a continuously
changing variable.
 critical angle – If light hits a boundary between two
materials at an angle greater than this, total internal reflection
occurs.
 digital signal – A signal that is represented by numbers
and can only be one of two states, i.e. 0 or 1.
 optical fibres – Long, thin strands of glass or plastic used
to carry digital signals as pulses of infrared or light.
 total internal reflection – An optical effect that occurs
when light hits a boundary between two materials at an angle
greater than the critical angle, so that all the light is reflected
and none is refracted.
1
19ofof20
21
© Boardworks Ltd 2005
2004
Anagrams
1
20ofof20
21
© Boardworks Ltd 2005
2004
Multiple-choice quiz
1
21ofof20
21
© Boardworks Ltd 2005
2004