Transcript Energy & Electricity

Year 11 GCSE
Physics
B2
COMMUNICATION
PHYSICS
(B2)
(B2)
LESSON 1 – History of
Communications
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.
(B2)
LESSON 2 – Microphones &
Loudspeakers
LEARNING OUTCOMES:
• Recall what loudspeakers, earphones,
microphones & tape heads do and explain
how they all work.
AUDIO TAPE
MICROPHONE
(B2)
LESSON 2 – History of
Communications
GROUP TASK:
MICROPHONES
LOUDSPEAKERS
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).
(B2)
LESSON 3 – Analogue &
Digital
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.
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.
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!!!
(B2)
LESSON 4 – AM and FM
Radio signals
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.
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 lowerfidelity 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.
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).
(B2)
LESSON 5 – Cathode Ray
Tubes & Oscilloscopes
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).
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.
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.
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.
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.
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!)
(B2)
LESSON 6 – Health Risks of
Mobile Phones
LEARNING OUTCOMES:
• Interpret given information about
developments in ideas about the potential
health hazards of mobile phones.