© boardworks ltd 2004 1 of 20 © boardworks ltd 2005 1 of 21 ks4 physics total internal reflection...

© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20051 of 21

KS4 Physics

Total Internal Reflection

and Communication


Total Internal Reflection and Communication

Contents

Total internal reflection

Digital and analogue

Storage and retrieval of information

Summary activities

Communication systems


Angle iAngle r

Angle r

Reflected ray

Incident ray

Refracted ray

At what angle of incidence did the ray change from refraction to reflection? It depends on the material used.

Angle i Angle r

Refraction or reflection

15°

30°

45°

60°

75°



Light ray simulation


This angle is called the critical angle ( c).

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.

i < c

Refraction

i = c

Critical case



How does the refractive index affect the critical angle?

The greater the refractive index, the smaller the critical angle.

Material Refractive index

Critical angle

Glass

Water

Diamond

42°

49°

24°

1.5

1.33

2.4

Research the missing values below and then make a conclusion.

The critical angle


Optical fibres, used in communication, use TIR.

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.

What are the applications of total internal reflection (TIR)?

You could be asked to draw on the path of the beam in an exam.



Optical vs. electrical

Research why communications systems now use optical fibres instead of copper wires.

Optical Electrical

Information

Attenuation

Interference

Cost

Carry more Carry less

Less More

No Yes

More Less

How is attenuation solved in optical and electrical fibres?

Regenerators for electrical cables

Repeaters for optical fibres



Contents




Summary activities



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?

Digital and Analogue


Advantages of digital

Signals are clearer and less susceptible to noise.

Can be used quickly by computers.

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.

Disadvantages

Digital hardware is expensive at the moment.

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.

What is noise?Noise is any unwanted

information.Examples of noise are?Electrical storms and

random thermal noise.Which signal is most

prone to noise?AnalogueWhich signal carries the

most information?Digital

Digital vs. analogue



Contents




Summary activities



Communication systems include the same basic components. You need to be able to define/describe the following:

Encoder

Amplifier

Decoder

Modulator

Transmitter

Receiver

Transducer

Storage



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).


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?

AM FMMore noise

Less noise More noise Less noiseTravels further

Travels further

Travels shorter distances

Travels shorter distances

Easier to send

Easier to send

Harder to send

Harder to send

AM and FM



Contents




Summary activities



What methods of storing audio and video information can you name?

1. _________________

2. _________________

3. _________________

4. _________________

Which are digital and which are analogue?

Compact disc - CD

Digital video disc - DVD

Magnetic tape

Vinyl records

Digital

Digital

Analogue

Analogue




Contents




Summary activities



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 reflectedand none is refracted.


Anagrams


Multiple-choice quiz

© boardworks ltd 2004 1 of 20 © boardworks ltd 2005 1 of 21 ks4 physics total internal reflection...

Documents