1. The World Communicates

2. The World communicates
Communication is the transfer of information from a sender to a receiver through a medium.
Most modern forms of communication rely on messages carried in one or more of the following modes:
An encoded electric current flowing along a wire (eg fixed telephone)
Optic fibres which carry an information signal encoded on a laser light beam (eg cable TV and some telephone lines).
Modulated electromagnetic waves travelling through a medium eg radio and free to air television

3. In this topic we focus on the transfer of energy using waves.
Energy: The ability or capacity to do work (measured in Joules or Kilojoules.
Waves: A wave is a travelling disturbance. Waves transport energy without transporting matter.

4. Waves

5. Syllabus reference
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.

6. Waves
Waves are a travelling energy disturbance. They are a means of transferring energy from one point to another without the physical movement of particles from one point to another (the particles merely oscillate). The source of all waves is a vibration. The energy of that vibration moving away from its source is the wave. The wave may radiate away from the source in one, two or three dimensions depending on the nature of the wave and the medium it passes through.

7. One dimensional wave motion along a spring or rope
One dimensional wave motion along a spring or rope. The medium (the spring) confines the wave to one dimension.

8. Two dimensional wave motion for example a ripple across a pond
Two dimensional wave motion for example a ripple across a pond. The wave travels outward from the origin across the surface thereby constricting the wave to two dimensions.

9. Three dimensional wave motion such as sound waves moving through air away from its source. Similarly light radiates in 3 dimensions from a point source.

10. Mechanical and non-mechanical waves
Some waves require a material medium in which to travel. These are called mechanical waves. Example of mechanical waves include sound waves, water waves, earthquake (seismic) waves and waves along a stretched spring or string.
Other waves called non-mechanical waves do not require a material medium to progress and are can therefore travel through a vacuum. These waves are created by changing fields. For example electromagnetic waves (such as light, infra red, X-rays) are caused by changing electrical and magnetic fields.

11. Wave types There are three main wave types:
Longitudinal waves
Transverse waves
Torsional waves
Each differs from the others in the way it distorts the medium as it travels through it.
See PowerPoint presentation “ Longitudinal and transverse wave motions”

12. Longitudinal and transverse waves
Read your text book and make a summary of longitudinal and transverse waves. Include:
Definitions which include a description of the oscillation of particles relative to wave motion
Examples of each type of wave
Diagram(s) showing rarefactions and compressions or crests and troughs, the wavelength and amplitude, direction of wave motion and direction of particle motion.

13. Classifying waves Waves (require a medium for transmission) Mechanical
Particles vibrate perpendicularly to direction of wave propagation
Transverse
Particles vibrate in same direction as wave propagation
Longitudinal
Non-mechanical e.g. electromagnetic radiation ( do not require a medium for transmission)
Electromagnetic radiation consists of transverse waves with alternating electric and magnetic fields at right angles to direction of wave travel

14. First hand investigation: Transmission of waves in slinky springs
Complete Investigation 1.1 “Investigating waves in a slinky spring” p13 Physics 1.
This investigation must be written up as a formal scientific report which will be marked.

15. Teacher Demonstration: Transmission of water waves.
Observe a demonstration of the propagation of water waves

16. Teacher Demonstration: Using an oscilloscope to gather information about the frequency and amplitude of waves.
After observing the demonstration of wave properties on the oscilloscope, draw sine wave representations for the following waves:
High frequency, low amplitude
Low frequency, low amplitude
High frequency, high amplitude
Low frequency, high amplitude

17. Video: Properties of Waves
Watch video “Properties of Waves” (ClickView)

18. Review
Complete Exercise sheet “Exercises – Part 1(from OTEN) provided.
Use your text and other sources to complete the “Glossary of key words and terms”.

19. = where The wave equation
The relationship between the velocity, frequency and wavelength of a wave is given by the equation
= where
 is velocity measured in metres per second ms-1
 is frequency measured in Hertz (Hz) i.e. waves per second
 is wavelength measured in metres (m)

20. Another equation
The (T) is the time it takes a single wave to pass a fixed point. It is the reciprocal of frequency or

21. Sample Problems
Carefully read the 3 sample problems on p4. In particular, note the setting out and the units.
Answer the questions set by your teacher.

22. First hand Investigation: The relationship between frequency and wavelength for sound waves.
Plan, choose equipment for and perform a first hand investigation to gather information to identify the relationship between the frequency and wavelength of a sound wave travelling at constant velocity.
This investigation must be written up as a formal scientific report which will be marked.

23. Sound
Sound waves are vibrations or oscillations of particles in a medium.

24. Sound waves cannot travel through a vacuum because there are no particles to vibrate (i.e. there must be a medium)

25. The compressions and rarefactions of sound waves (longitudinal waves) can be represented by the crests and troughs of transverse waves.

27. Sound waves represented as transverse waves
Complete the worksheet “Sound waves represented as transverse waves”.

28. Pitch and frequency
The pitch of a sound is related to the frequency of its wave. A high pitched sound has a high frequency and a low pitched sound has a low frequency.

29. Syllabus reference
Perform a first-hand investigation and gather information to analyse sound waves from a variety of sources using the Cathode Ray Oscilloscope (CRO) or an alternate computer technology

30. A cathode ray oscilloscope converts sound waves into a sine wave

32. Review
Complete Exercise sheet “Exercises – Part 2 (from OTEN) provided.
Use your text and other sources to complete the “Glossary of key words and terms”.

33. An echo occurs as the result of the sound wave being reflected from a surface.

34. The principle of superposition
When two or more waves of the same type pass through the same medium at the same time, the displacement of any point is the sum of the individual displacements.