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1. d

   • Using light increases the speed of communication
   • Total internal reflection is when a wave stays inside a material by bouncing off the internal walls.
   • Total Internal Reflection occurs when the angle of incidence is bigger than the critical angle for the materials.
   • If the angle of incidence is too small the light will leave the material rather than staying inside.
   • Lasers produce an intense, narrow beam of light of a single colour (monochromatic).
   • The waves in a laser beam are coherent, which means they are all in phase
   • Lasers can be used in surgery and dental treatment, for cutting materials in industry, weapon guidance and in laser light shows
   • Morse code is a series of on off signals, which means it is digital
   • Laser beams are used to read information from CDs in CD players. The shiny surface of a CD contains billions of microscopic pits in a spiral track. The pattern of pits contains digital information. The laser light is reflected off the surface of the CD as the disk spins, and is detected by:
     • the change in the amount of reflected light caused by entering or leaving a pit is interpreted as a 1
     • no change in the amount of reflected light is interpreted as a 0.
   • Information such as computer data and telephone calls can be converted into electrical signals. These can be carried through cables, or transmitted as microwaves or radio waves. However, the information can also be converted into either visible light signals or infrared signals, and transmitted by optical fibres.

2. f

   • Analogue signals have a continuously variable value
   • Digital signals are either on (1) or off (0)
   • Everyday uses of infrared radiation include: remote controls and short distance data links
   • Infrared sensors detect body heat
   • The advantages of using digital signals include: that it is easier to remove noise and you can use multiplexing.
   • Multiplexing is when you send more than one signal on a carrier wave
   • The advantages of using optical fibres include: multiplexing and lack of interference in the final signal.
   • Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude than the amplitude of the ON states. As a result, the electronics in the amplifiers can ignore the noise and it does not get passed along.
   • Optical fibres can carry more data because of multiplexing. This is where several digital signals are interleaved or carried together without being mixed. Digital radio and TV broadcasts also carry more data than analogue broadcasts: they can also be multiplexed. This allows for a more efficient use of the available radio frequencies
   • Television remote controls use infrared light to transmit coded signals to the television set in order to, for example, change channels or adjust the volume.

3. g

   • Wireless technology uses electromagnetic radiation
   • The advantages of wireless technology are: no external/direct connection to a telephone needed, portable and convenient, allows access when on the move.
   • The advantages of DAB radios are: more stations available, less interference with other broadcasts
   • The disadvantages of DAB radios are: poorer quality compared to FM, not all areas covered.
   • Radiation used for communication is refracted and reflected and this can be an advantage or disadvantage for good reception
   • Common uses of wireless technology include: TV and radio, mobile phones and laptop computers.
   • Radio waves (like light) exhibit total internal reflection
   • The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the ionosphere. This means that they can still reach receivers that are not in the line of sight because of the curvature of the Earth's surface.

4. e

   • The best emitters and absorbers are dull and black.
   • The worst emitters and absorbers (and so best reflectors) are shiny and white.
   • Mobile phones use microwave signals
   • Properties of infrared radiation include: heats the surface of the food and is reflected by shiny surfaces.
   • Infrared is absorbed only by particles on the surface of the food increasing their energy.
   • This energy is then transferred to the rest of the food by conduction and convection.
   • Properties of microwave radiation include: they penetrate (about 1cm) into food, are reflected by shiny metal surfaces, can cause burns when absorbed by body tissue and can pass through glass and plastics.
   • Water and fat absorb microwaves
   • Microwaves are absorbed only by water and fat in the outer layers of the food increasing their KE.
   • When microwaves transmit information there is some signal loss due to interference, the curvature of the earth, no diffraction around objects and adverse weather
   • The evidence of dangers from mobiles is not conclusive
   • Therefore it is not easy to decide on the siting of phone masts
   • As you increase the frequency of a microwave the energy increases