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3.3.4Waves

Communications — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 29 of 35 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

3.3.4 Communications — IGCSE PHYSICS notes: Explain how radio waves, microwaves, infrared and visible light are used to communicate, including satellites and optical fibres.Waves used — microwavesLow orbit satellitesOrbit about 200 km above sea levelUsed for monitoring weather, m…

  • Other advantages
  • Wavelength
  • Diffraction
  • Fibre advantages
  • Fibre cables
  • Signal strength

Part 1 of 7Communications with satellites

Waves used
  • Waves used microwaves
Low orbit satellites
  • Orbit about 200 km above sea level
  • Used for monitoring weather, military applications and imaging Earth's surface
  • Shorter signal delay and clearer signals
  • More than one satellite is needed for continuous operation
  • Polar orbit satellites are low Earth orbit satellites that orbit around the poles
Geostationary satellites
  • Orbit above the equator at 36 000 km
  • Orbit time of 24 hours so they stay above the same point
  • Used for radio and telecommunication broadcasting worldwide
  • Used by some satellite phones and direct broadcast satellite television

Part 2 of 7Microwaves

Use
  • Use mobile phones, wireless internet and satellite television
Range
  • Range transmit signals over large distances
Masts
  • Masts mobile networks use microwave masts to relay signals from the nearest mast to the phone
Obstacles
  • Obstacles masts cannot be too far apart because hills or the curvature of the Earth diffract the beam
Satellites
  • Satellites microwaves are not refracted, reflected or absorbed by the atmosphere or ionosphere, so signals can be relayed around the Earth
Other advantages
  • Other advantages they penetrate most walls and need only a short aerial

Part 3 of 7Radio waves

Use
  • Bluetooth, terrestrial television and local radio stations
Wavelength
  • Wavelength around a kilometre for some radio waves
Diffraction
  • Diffraction radio waves diffract around hills because their wavelength is similar to the size of the hill
Bluetooth
  • Bluetooth uses radio waves instead of wires over short distances
  • Shorter wavelengths allow high data rates over short distances
  • Signals pass through walls but are weakened

Part 4 of 7Optical fibres

Waves used
  • Waves used visible light and short-wavelength infrared
Uses
  • Uses cable television and high-speed broadband
Data rate
  • Data rate high frequency allows high data rates
Principle
  • Principle total internal reflection along the fibre

Part 5 of 7Choosing the right technology

MethodAdvantagesLimits
RadioLong range, passes obstaclesLow data rate
MicrowavesHigh data rate, satellite linksNeeds line of sight
InfraredCheap, no interference between roomsVery short range
Optical fibreVery high capacity, secure, low lossNeeds cable laid

Part 6 of 7Comparing transmission methods

Fibre advantages
  • Fibre advantages more information, less signal loss and no electrical interference
Fibre cables
  • Fibre cables run under the sea and form the backbone of the internet
Bandwidth
  • Bandwidth higher-frequency carriers allow more data per second
Signal strength
  • Signal strength falls with distance for radio and microwaves, and dishes keep the beam narrow

Part 7 of 7More from the specification

More from the specification
High frequency radiation and solar cells
  • High frequency radiation and solar cells satellite transponders utilize high-speed electromagnetic signals powered by photovoltaic cells while avoiding penetrating x-rays.
Artificial satellite
  • A man-made object orbiting a body in space.
Digital signal
  • Signal that has only two states, 1 and 0
Analogue
  • Instrument displaying a quantity by pointer position or liquid level on a scale.
Ultraviolet
  • Radiation of shorter wavelength than visible light that can damage skin.
Spectrum
  • Range of colours in white light.
Radiation
  • Transfer by electromagnetic waves, requiring no medium
X-ray
  • A high-frequency electromagnetic wave produced when fast electrons are stopped by a metal target.
Transmission
  • Sending electricity along power cables from the power station to consumers.
Electromagnetic wave
  • Transverse wave that transfers energy from a source to an absorber
Electromagnetic spectrum
  • Continuous family of waves from radio waves to gamma rays

Key terms

TermMeaning
Geostationary satelliteSatellite orbiting above the equator in 24 hours at 36 000 km
Low orbit satelliteSatellite about 200 km up with a short signal delay
Optical fibreThin glass strand that carries light by total internal reflection
BluetoothShort-range wireless link using radio waves
DiffractionSpreading of waves around obstacles

Avoid these mistakes

1
Saying satellites use radio waves — communications with satellites use microwaves.
2
Saying a geostationary satellite is not moving — it orbits once in 24 hours with the Earth.
3
Saying radio diffracts because it is small — the wavelength is similar to the size of the hill.
4
Naming a technology without matching the wave — state the wave used.

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