1. AQA Physics Waves Section 1 Introduction and Definitions in Waves

2. The Origin of Waves Waves originate from a disturbance in a medium. Mechanically this can be due to vibrations between physical molecules. Waves can also however originate from disturbances is electromagnetic fields. A wave is a mechanism of transferring energy from one place to another by the means of a pattern or disturbance. For the present, we will restrict our arguments to mechanical oscillations.

3. Transverse Waves Transverse waves: Where the displacement is perpendicular to the direction of the wave. C T T T C C The peak of a transverse wave is known as the crest (C). The bottom of a transverse wave is known as a trough (T).

4. Longitudinal Waves Longitudinal waves: Where the displacement is parallel to the direction of the wave. The point in a longitudinal wave where the particles are squashed together is known as a compression (C). The point in a longitudinal wave where the particles are spread out is known as a rarefaction (R). C C C R R R

5. Oscillations A mechanical wave is made up of several particles that oscillate about a central position. Time Displacement The displacement of this motion can be represented with respect to time on a displacement-time graph. A The amplitude of a wave is the maximum displacement from the central position.

6. The time period (T) tells us how long it takes for a point in the wave to complete one cycle. [T] = seconds Time Period and Frequency The frequency (f) tells us how many cycles have occurred in one second. [f] = s -1 = Hz Time /s Displacement T 0.5 1.0 1.5

7. Phase tells us what point the disturbance is in its cycle. Phase Time Disturbance

8. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

9. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

10. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

11. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

12. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

13. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

14. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

15. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

16. Phase tells us what point the disturbance is in its cycle. Time Disturbance Phase

17. 0º 0 (or 2  )

18. 45º  /4

19. 90º  /2

20. 135º 3  /4

21. 180º 

22. 225º 5  /4

23. 270º 3  /2

24. 315º 7  /4

25. 0 or 360º 0 or 2 

26. Comparing the Phase of two Waves A comparison between two waves or disturbances in a wave can be made by examining their phase difference. Phase difference is 0°, 0  radians or 0 - in phase

27. Comparing the Phase of two Waves A comparison between two waves or oscillations in a wave can be made by examining their phase difference. Phase difference is 180°,  radians or /2 – anti-phase

28. Comparing the Phase of two Waves A comparison between two waves or oscillations in a wave can be made by examining their phase difference. Phase difference is 90°,  /2 radians or /4

29. Comparing the Phase of two Waves A comparison between two waves or oscillations in a wave can be made by examining their phase difference. Two waves that have a fixed phase relationship are known to be “coherent”.

30. The wavelength ( ) is the minimum distance between two disturbances that are in phase with each other. [ ] = m Wavelength ( ) distance Disturbance 4.0 8.0 12.0

31. Wave fronts are a series of lines that represent consecutive parts of the wave that are in phase. Wave Fronts The distance between wave fronts is of course the wavelength. distance Disturbance

32. Sketching using wave fronts makes it easier to show 2-dimensional waves such as circular waves. Wave Fronts

33. The wave speed refers to the speed of propagation of the wave pattern. Remember, the particles on a mechanical wave DO NOT propagate with the wave pattern (envelope). Wave Speed The speed of the wave (v) is determined by the product of the wavelength ( ) and the frequency (f).