1. Waves Wave characteristics

2. Travelling Waves v There are two types of mechanical waves and pulses that we encounter in the physical world.

3. Transverse v In these waves the source that produces the wave oscillates at right angles to the direction of travel of the wave v It means that the particles of the medium through which the wave travels also oscillates at right angle to the direction of travel of the wave.

4. Direction of travel of the wave Direction of oscillation of the particles Transverse Wave

5. Longitudinal v In these waves the source that produces the wave oscillates in the same direction as the direction of travel of the wave v It means that the particle of the medium through which the wave travels also oscillates in the same direction as the direction of travel of the wave.

6. Longitudinal Wave Direction of travel of the wave Direction of oscillations of the particles

7. Transverse Waves

8. Longitudinal Waves

9. What is a Wave? v A wave is a means by which energy is transferred between two points in a medium without any net transfer of the medium itself.

10. The Medium v The substance or object in which the wave is travelling. v When a wave travels in a medium parts of the medium do not end up at different places. v The energy of the source of the wave is carried to different parts of the medium by the wave.

11. v Water waves however, can be a bit disconcerting; v Waves at sea do not transport water but the tides do. v Similarly, a wave on a lake does not transport water but water can actually be blown along by the wind.

12. Displacement v (d) is the distance that any particle is away from its equilibrium position at any given time. v Measured in meters

13. Amplitude v (A, a) This is the maximum displacement of a particle from its equilibrium position. v (It is also equal to the maximum displacement of the source that produces the wave). v Normally measured in meters

14. Period v (T) This is the time that it takes a particle to make one complete oscillation. v (It also equals the time for the source of the wave to make one complete oscillation). v Measured in seconds

15. Frequency v (f) This is the number of oscillations made per second by a particle. v (It is also equal to the number of oscillations made per second by the source of the wave) v The SI unit of frequency is the hertz - Hz. (1 Hz is 1 oscillation per second) v So, f = 1/T

16. Wavelength v ( ) This is the distance along the medium between two successive particles that have the same displacement and the same phase of motion. v Ex. Distance between two consecutive wave crests. v Measured in meters

17. Wave Speed v (v, c) This is the speed with which energy is carried in the medium by the wave. v Measured in m/s v A very important fact is that wave speed depends only on the nature and properties of the medium.

18. Crest v This is a term coined from water waves and refers to the points at the maximum height of the wave.

19. Trough v A term coined from water waves referring to the points at the lowest part of the wave.

20. Wavelength again! v Wavelength will therefore be equal to the distance between successive crests and/or successive troughs.

21. Compression v This is a term used in connection with longitudinal wave and refers to the region where the particles of the medium are "bunched up". v High density v High pressure

22. Rarefaction v A term used in connection with longitudinal waves referring to the regions where the particles are "stretched out". v Low density v Low pressure

23. Longitudinal Waves v The wavelength will be equal to the distance between successive points of maximum compression and/or successive points of maximum rarefaction. v The compression is the region in which the molecules of the air are pushed together. v The rarefaction is the region where the molecules move apart.

24. rarefactions wavelength

25. Sound Waves v A longitudinal wave in a slinky spring is analogous to a sound wave in which each turn of the spring represents an air molecule.

26. Interpreting Graphs - 1 displacement distance crest trough amplitude crest wavelength amplitude wavelength

27. Interpreting Graphs - 2 displacement time amplitude period

28. Deriving v = f v Imagine a wave with velocity v v Being produced from a source of frequency f v In 1 second the 1 st wavefront would have travelled a distance of f v As speed = distance / time v v = f / 1 v  v = f

29. 2 Important Points v 1. The frequency of a wave depends only on the source producing the wave. w It will therefore not change if the wave enters a different medium or the properties of the medium change

30. v 2. The Speed of waves only depends on the nature and the properties of the medium. w Water waves do travel faster in deeper water w Light waves do travel slower in more optically dense material. w Sound waves do travel slower in cold air

31. The EM Spectrum Itself Short Long High fLow f VISIBLE Radio Waves Micro Waves Infra red Gamma rays Ultra Violet X rays

32. Frequencies of Regions (Hz) Gamma Rays >10 21 X-rays 10 17 - 10 21 Ultraviolet 10 14 - 10 17 Violet 7.5 x 10 14 > Visible > Red 4.3 x 10 14 Infrared 10 11 -10 14 Microwaves 10 9 -10 11 Radio and TV < 10 9

33. The Different Regions v In the context of wave motion, common properties of all parts of the electromagnetic spectrum are w all transverse waves w all travel at the speed of light in vacuum (3.0 x 10 8 m/s) w all can travel in a vacuum

34. Sources of Regions w Gamma – certain radioactive material’s nuclei w X-rays – by firing an electron stream at a tungsten metal target in a highly evacuated tube. w Ultraviolet – the Sun, ultraviolet lamp w Visible – hot bodies w Infrared – the Sun (heat), hot bodies w Microwaves – Ovens, communication systems w Radio and TV – transmitter stations, Azteca TV