P1 d-f

P1 d-f

1. E

   • Microwaves
     • Water and fat absorb microwaves
     • Microwaves are absorbed only by water and fat in the outer layers of food increasing their kinetic energy
     • When microwaves transmit information there is some signal due to interfence, the curvature of the earth, no diffraction around objects and adverse weather
     • 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 plastic
   • Infrared
     • Infrared is absorbed by only the particles on the surface of food increasing their energy.
       • The energy is then transferred to the rest of the food by conduction and convection
     • Properties of infrared radiation include: heats the surface of food and is reflected by shiny surfaces
   • Mobile phones
     • Mobile phones use microwave signals
     • The evidence of dangers from mobiles is not conclusive
       • Therefor it is not easy to decide on the siting of phone masts
   • Emitters
     • The worst emitters and absorbers (and so best reflectors) are shiny and white
     • The best emitters and absorbers are dull and black

2. F

   • Infrared
     • Everyday uses of infrared radiation include: remote controls and short distance data links
     • Infrared sensors detect body heat
   • Signals
     • Analogue
       • Analogue signals have a continuously variable value
     • Digital
       • The advantages of using digital signals include: that it is easier to remove noise and you can use multiplexing
       • Digital signals are either on (1) or off (0)
   • Multiplexing
     • Multiplexing 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

3. D

   • Lasers
     • The waves in a laser beam coherent, which means they are inn phase
     • Laser can be used in surgery and dental treatment, for cutting materials in industry, weapon guidance and in laser light shows
     • Lasers produce an intense, narrow beam of light in a single colour
   • Morse code is a seris of on off signals, which means it is digital
   • Using light increases the speed of communication
   • Total internal reflection
     • Total internal reflection when a wave stays inside a material by bouncing off the internal walls
     • Total internal reflection occurs when the angle of incidence is equal to or 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