B2 COMMUNICATION PHYSICS

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B2COMMUNICATIONPHYSICS
(B2)

• Year 11 GCSE Physics

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LESSON 1 History of Communications
(B2)

• LEARNING OUTCOMES
• Appreciate how historically the use of light
  greatly increased the speed of communication, but
  that it requires use of code.
• Appreciate how the use of electrical signals has
  improved the speed distance of communication.
• Know that radio, TV, fax, telephone, e-mail,
  internet can be used to rapidly send information
  long distances.
• Explain the merits of light radio waves for
  communication.

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LESSON 2 Microphones Loudspeakers
(B2)

• LEARNING OUTCOMES
• Recall what loudspeakers, earphones, microphones
  tape heads do and explain how they all work.

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AUDIO TAPE
MICROPHONE
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LESSON 2 History of Communications
(B2)
GROUP TASK MICROPHONESLOUDSPEAKERS AUDIO TAPE
PLAYER Time 30 minutes Produce a PowerPoint in
teams of 3 - 4 on 1 of the objects above, to show
a cutaway view of what happens and include
relevant physics terminology explanations. At
the end each group will show their PowerPoint and
ask class which aspects of their own and each
others they thought were most clear and if there
were any misconceptions or area to improve (peer
assessment).
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LESSON 3 Analogue Digital
(B2)

• LEARNING OUTCOMES
• Recall the difference between analogue digital
  signals and recognise that the latter requires an
  extension of the idea of a code for transmitting
  information.
• Describe some of the benefits of digital coding
  of information, and how it is used to record on
  CDs and transmit information through optical
  fibres, and the advantages of using digital
  recording playback using CD compared with
  magnetic tape and vinyl.

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ANALOGUE signals can have any value. This makes
them difficult to copy and store and prone to
interference. They are used for recordings on
audio and video tape, vinyl and am radio
broadcasts.
DIGITAL signals can only have 2 values O
and 1, corresponding to OFF and ON in the
transistors in electronic devices. This allows
them to be copied almost endlessly with no loss
of signal or interference, they can be easily
stored and compressed, and give better quality.
They are used for modern phone communications and
DAB, digital ( SKY) TV, CD, DVD and MP3.
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SAMPLING allows the height (amplitude) of an
analogue signal to be measured at regular time
intervals (often millionths of a second) the
height is then turned into a number and converted
to binary (eg, a height of 9 in binary is 1001).
Sampling too infrequently will produce a less
accurate signal (eg, the poor guitar sound on a
cheap keyboard).
Poor sampling!!!
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LESSON 4 AM and FM Radio signals
(B2)

• LEARNING OUTCOMES
• Describe the operation of an amplitude modulated
  (AM) radio system, including the processes of
  carrier wave production modulation,
  transmission of signal and reception, diode
  detection and amplification.

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AM was the dominant method of broadcasting during
the first two thirds of the 20th century and
remains widely used into the 21st. The Central
Intelligence Agency World Factbook lists
approximately 16,265 AM stations worldwide.
Because of its susceptibility to atmospheric
interference and generally lower-fidelity sound,
AM broadcasting is better suited to talk radio
and news programming, while music radio and
public radio mostly shifted to FM broadcasting in
the late 1960s and 1970s.
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So how does a radio wave carry sounds such as
voice or music to your radio receiver? The radio
station broadcasts a carrier wave at the
station's assigned frequency. The carrier wave is
modulated (varied) in direct proportion to the
signal (e.g., voice or music) that is to be
transmitted. The modulation can change either the
amplitude or the frequency of the carrier
wave. The "AM" in AM radio stands for "amplitude
modulation," and the "FM" in FM radio stands for
"frequency modulation." A radio receiver removes
the carrier wave and restores the original signal
(the voice or music).
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LESSON 5 Cathode Ray Tubes Oscilloscopes
(B2)

• LEARNING OUTCOMES
• Appreciate that the behaviour of electron guns
  in cathode ray tubes can be explained in terms of
  negatively charged particles given off from a
  heated wire and then accelerated.
• Recall the principles of the cathode ray tube
  apply this knowledge to the oscilloscope
  (including X and Y plates, volts/cm. time base
  and intensity controls) and television (including
  scan patterns brightness control via
  modulator).

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The cathode ray tube (CRT), invented by German
physicist Karl Ferdinand Braun in 1897, is an
evacuated glass envelope containing an electron
gun (this is just a wire filament heated by a low
voltage, so that it boils off electrons we
call this process THERMIONIC EMISSION) and a
fluorescent screen, usually with internal or
external means to accelerate and deflect the
electrons. High potential anodes attract
accelerate electrons, magnetic field plates
(deflection coils) move the electons around the
screen. When electrons strike the fluorescent
screen, light is emitted.
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The electron beam is deflected and modulated in a
way which causes it to display an image on the
screen. The image may represent electrical
waveforms (oscilloscope), pictures (television,
computer monitor), echoes of aircraft detected by
radar, etc. The single electron beam can be
processed in such a way as to display moving
pictures in natural colors. The generation of an
image on a CRT by deflecting an electron beam
requires the use of an evacuated glass envelope
which is large, deep, heavy, and relatively
fragile. The development of imaging technologies
without these disadvantages has caused CRTs to be
largely displaced by flat plasma screens, liquid
crystal displays, DLP, OLED displays, and other
technologies.
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OSCILLOSCOPES These use a CRO connected to
voltage inputs. The dot is swept across the
screen (X direction) by a TIME BASE CONTROL. Each
square on the screen horizontally represents a
set time (eg, 1ms per division) allowing the
period and frequency of the signal to be worked
out. If the dot moves fast enough then the human
eye sees it as a continuous wave. The Y direction
is the voltage control, setting the sensitivity
of the oscilloscope. This allows the amplitude of
the signal to be measured.
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TELEVISIONS A standard monitor screen is a CRT
(cathode ray tube). The screen is coated on the
inside surface with dots of chemicals called
phosphors. When a beam of electrons hits a dot,
the dot will glow.  On a color monitor these
phosphor dots are in groups of three Red, Green,
and Blue. This RGB system can create all the
other colors by combining what dots are
aglow. There are 3 signals that control the 3
electron beams in the monitor, one for each RGB
color. Each beam only touches the dots that the
signal tells it to light. The beams rapidly cover
a scanning pattern across the screen in a
fraction of a second. All the glowing dots
together make the picture that you see. The human
eye blends the dots to "see" all the different
colors.
TELEVISIONS
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• Scanning must satisfy several criteria.
• The separation between scan lines must be
  sufficiently close so that individual scan lines
  cannot be perceived at a reasonable viewing
  distance.
• Scan line separation and the bandwidth allocated
  to the video signal define the image's resolution
  (the limiting fine detail visible in the image).
  Resolution must be the same horizontally and
  vertically.

• The speed at which we scan must be fast enough so
  that the frame flicker cannot be perceived.
• Achieving acceptable quality pictures within
  bandwidth constraints counterbalances resolution
  flicker requirements. A shadow mask blocks the
  path of the beams in a way that lets each beam
  only light its assigned color dots. (cool
  trick!) 

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LESSON 6 Health Risks of Mobile Phones
(B2)

• LEARNING OUTCOMES
• Interpret given information about developments
  in ideas about the potential health hazards of
  mobile phones.