8.2 The World Communicates
Contextual Outline: (BOS Syllabus - p. 21)
The discovery of electricity and then the electromagnetic spectrum has led to the rapid increase in the number of communication devices throughout the twentieth century. The carrier of the information is no longer a vehicle or person - rather, an increasing range of energy waves is used to transfer the message. The delay in relaying signals around the world is determined only by the speed of the wave, and the speed and efficiency of the coding and decoding devices at the departure and arrival points of the message. The time between sending and receiving messages through telecommunications networks is measured in fractions of a second allowing almost instantaneous delivery of messages, in spoken and coded forms, around the world.
This module increases students' understanding of the nature, practice, application and uses of physics and current issues, research and developments in physics.
Assumed Knowledge (BOS Syllabus - p. 21)
- identify waves as carriers of energy and qualitatively describe features of waves including frequency, wavelength and speed
- give examples of different types of radiation that make up the electromagnetic spectrum and identify some of their uses
- distinguish between the absorption, reflection, refraction and scattering of light and identify everyday situations where each occurs
- identify that some types of electromagnetic radiation are used to provide information about the universe
- describe some everyday uses and effects of electromagnetic radiation, including applications in communication technology.
The Basic Wave Model (BOS Syllabus - p. 25)
- Identify that mechanical waves require a medium for propagation while electromagnetic waves do not (hence electromagnetic radiation travels through empty space or a vacuum wheareas a mechanical wave such as a sound wave does not)
- Define and apply the following terms to the wave model: wave frequency, wavelength, wave velocity, propagation medium, displacement, amplitude, period, compression, rarefaction, crest, trough
- Distinguish between transverse waves and longitudinal waves and describe the relationship between particle motion and the direction of energy propagation in transverse and longitudinal waves
- Describe waves as a transfer of energy disturbance that may occur in one, two or three dimensions, depending on the nature of the wave and the medium
- Quantify the relationship between wave velocity, wave frequency and wavelength for a wave (v = f l)
- In the context of a wave model describe the energy transformations in one of the following communication devices:
- mobile telephone
- radio and television
- sound waves traveling through a propagation medium do so by vibrating particles in a the medium causing them to oscillate back and forth in the direction of wave travel (sound waves are therefore transverse waves)
- relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them
- explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves
- echos are caused by sound waves bouncing back (reflecting) off substances
- the principle of wave superposition provides for waves passing each other to "add up". This can cause constructive or destructive interference.