GENERAL PROPERTIES OF WAVES

1. GENERAL PROPERTIES OF WAVES INTRODUCTION TO WAVES Mr Elijah Ong

2. Tsunami Mr Elijah Ong

3. Uses of waves • What are some examples or applications of waves in everyday life? • Hydropower • Guitar/piano, in fact all musical instruments • The above are mechanical waves • Some electromagnetic waves includes light, radio waves, x-rays Mr Elijah Ong

4. Kallang Waves! Mr Elijah Ong

5. What is a wave? • Spreading of disturbance from one place to another. • The source is a vibration or oscillation. • Energy is transferred from one point to another WITHOUT physical transfer of any material between the two points Mr Elijah Ong

6. Demo WAVES • Slinky or ropes • Transverse waves • http://www.ngsir.netfirms.com/englishhtm/TwaveA.htm Mr Elijah Ong

7. Transverse Waves • Transverse waves travel in a direction PERPENDICULARto the direction of the vibrations. Mr Elijah Ong

8. Mr Elijah Ong

9. Transverse Waves Some Examples: • water waves • rope waves • electromagnetic waves (example: light) Mr Elijah Ong

10. The Slinky Coil What do you notice about the direction of the vibrations and the direction of the wave? Mr Elijah Ong

11. The other type of wave called… … Longitudinal Wave… • What is a longitudinal wave? • A wave where the direction of travel is parallel to the direction of vibration. Mr Elijah Ong

12. How does it look like? • Demonstration of a longitudinal wave? • Slinky Coil • On an Applet Mr Elijah Ong

13. Longitudinal Waves • Compression • Places where air pressure is slightly higher than the surrounding air pressure. • Rarefaction • Places where air pressure is slightly lower than the surrounding air pressure. Mr Elijah Ong

14. Longitudinal Waves • Examples - Sound waves Mr Elijah Ong

15. Compression Rarefactions Compression LONGITUDINAL WAVES • Longitudinal waves travel in a direction PARALLEL to the direction of vibrations. • We use compressions and rarefactions to describe them Mr Elijah Ong

16. Demo on applet • http://www.ngsir.netfirms.com/englishhtm/Lwave.htm Mr Elijah Ong

17. Example Q. A sound wave in air has a frequency of 262Hz and travels with a speed of 343m/s. How far apart are the wave compressions? A. Given f = 262 Hz and v = 343m/s, Distance between wave compression = wavelength = v / f = 1.3m (1 dp) Mr Elijah Ong

18. Wavefront • That is a… wavefront - an imaginary line on a wave that joins all points which have the same phase of vibration. Mr Elijah Ong

19. CREST CREST Crests and Troughs • Crests: points of maximum displacement on a wave • Troughs: points of minimum displacement on a wave displacement Distance along rope TROUGH Mr Elijah Ong

20. AMPLITUDE (A) • Maximum Displacement from the rest or central position. • SI unit metre (m) displacement crest crest amplitude distance along rope amplitude trough Mr Elijah Ong

21. Wavelength (λ) • The distance between two successive points of the same phase. Example: distance between two crests. SI unit: metre (m). displacement Wavelength crest λ crest amplitude position along rope amplitude trough Mr Elijah Ong

22. Frequency (f) • Number of complete waves generated per second (or number of cycles/oscillations per second) • SI unit: hertz (Hz) • E.g: 5 Hz mean 5 waves generated in 1s Mr Elijah Ong

23. Period (T) • Time taken to generate one complete wave (or to complete one cycle) • SI unit: second (s) • E.g. • 5 Hz mean 5 waves generated in 1s • 1 wave is generated in 1/5 = 0.25 s • Therefore, Period (T) = 0.25s Mr Elijah Ong

24. Relationship between T and f As f increases, T decreases Mr Elijah Ong

25. How fast is the wave moving? Mr Elijah Ong

26. Find the velocity of waves Velocity of wave is the product of its frequency and wavelength Mr Elijah Ong

27. Example Q. A fisherman notices that wave crests pass the bow of his anchored boat every 3.0s. He measures the distance between two successive crests to be 6.5m. How fast are the waves travelling? A. From the question, we know the period, T = 3.0s, and the wavelength is 6.5m. Therefore, wave speed, v = 6.5 / 3 = 2.2ms-1 (1 dp) Mr Elijah Ong

28. Using the 2 formulas, can you combine them and formed a third equation? Third equation: Mr Elijah Ong

29. 2 types of graphs to note! • The displacement-position graph • Able to find wavelength • Amplitude • The displacement-graph • Period • Amplitude Mr Elijah Ong

30. Displacement-time graph • Distance between two crests denotes the period in a displacement-time graph.( Contrast this with the displacement-position graph! What is the difference?) displacement Period crest T crest amplitude time amplitude trough Mr Elijah Ong

31. Displacement-time and displacement-position graphs Displacement-time graph： Shows the displacement of ONE particle (from the rest position) at different times. ONE at different times Displacement-position graph： Shows the displacement of ALL particles at a certain time. ALL at a certain time Mr Elijah Ong

32. Try this • Textbook page 177 Mr Elijah Ong

33. Question motion of wave ? ? wave at next moment wave at this moment Particles in the medium vibrate when the wave passes by. In which direction does the particle move? Mr Elijah Ong

34. Question Downwards. To the right. Other： _______ In which direction does particlea move? motion of wave ? wave at this moment ? wave at next moment Mr Elijah Ong

35. Vibration vs Waves • Vibrations simply refers to one single particle vibrating at its mean position • Waves refer to the all the particles’ vibrations with respect to time • They are essentially different! Don’t mix these two terms up. Mr Elijah Ong

36. SUMMARY Mr Elijah Ong