B2COMMUNICATION

PHYSICS

Year 11 GCSE Physics (B2)

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.

LESSON 2 – Microphones & Loudspeakers

(B2)

LEARNING OUTCOMES:

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

AUDIO TAPE

MICROPHONE

LESSON 2 – History of Communications

(B2)

GROUP TASK:

MICROPHONESLOUDSPEAKERS

AUDIO TAPE PLAYER

Time = 30 minutesProduce 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).

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.

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.

Poor sampling!!!

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).

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.

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.

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).

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).

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!) 

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.