6. Waves in a string quarter wave half wave three quarter wave full wave (one complete wave) vibrating source one complete vibration half vibration Direction of wave No vibration
7. Waves in a string vibrating source two complete vibration two waves
9. Transverse Waves Transverse waves are waves in which the particles of the medium move at right angle to the direction of wave motion. wave direction vibration of particle
10. Water waves are produced by the water particles’ vibration. Water Waves
11. Cross-section of a water wave crest crest crest Crest is referred to the top of the wave. Trough is referred to the bottom of the wave. trough trough trough
12. Motion of particles in Transverse waves Particles are moving perpendicular to the wave motion. No forward motion of particles in the wave. wave direction main position or rest position
13. Motion of particles in a wave starting upwards particle first wave particle in second wave
14. Motion of particles in a wave starting downwards particle first wave particle in second wave
15. Wave direction 2nd wave 1st wave Wave moves forwards and particles either move up or down perpendicular to the wave direction.
16. Show the directions of the particles labelled with letters. motion of wave A B C D E F G
17. Show the directions of the particles labelled with letters. motion of wave A B C D E F G
18. Amplitude and wavelength 1 Amplitude : Amplitude of a wave is the maximum displacement made by the particle from its rest position. wave motion rest position amplitude amplitude amplitude amplitude
19. Wavelength is the distance between two successive particles which are at exactly the same point in their paths and are moving in the same direction . 2 Wavelength ( ): wavelength wavelength wavelength
20. Q1 A transverse wave is travelling to the right along a rope. The diagram below represents a photograph of the wave pulse at a particular instant. P Q direction of wave motion The movement of the particles P and Q at the instant will be P Q A downward downward B upward downward C downward upward D upward upward
21. Q2 The diagram below shows the profile of a transverse wave. Which distance represents one wavelength? A BD B EF C EH D GH A B C D G F H E
22. Q3 The diagram shows a ball floating in a tank of water Which diagram shows the movement of the ball when the wave passes? A B C D direction of wave ball
23. Wavelength is the length of one complete wave. 1 wave wavelength
24. 3 Period (T) Period is the time taken for one complete vibration or oscillation. Period of an oscillation is 1.5 s. It means that 1.5 s is needed to complete one oscillation.
25. 4 Frequency ( Frequency is the number of complete vibrations or oscillations per unit time. or Frequency is the number of complete waves leaving the wave source per unit time.
26. Unit for frequency: The hertz (Hz) 1 Hz is one complete vibration or oscillation in second. E.g. If a source produces 5 complete waves in second, the wave frequency is 5 Hz. If a pendulum made 50 complete oscillations in 40 s what is its frequency? frequency , = 50 40 = 1.25 Hz
27. Relationship between frequency and period Let T = period in s = frequency in Hz or e.g. The period of a pendulum is 0.25 s what is its frequency? = 1 T T = 1
28. 5 Wave speed: Wave speed is the speed at which the waves move through the medium. The frequency depends on the source; The wave speed depends only on the medium the waves are travelling through.
29. Wave equation: If a source produces waves at a frequency of 5 Hz. That is, it produces 5 complete waves per second. If the wavelength of the wave is 2 m, the waves will move forward by 5 x 2 m in one second. Its speed is 10 m/s. 1 2 3 4 5
30. Wave speed = frequency x wavelength Let v = wave speed in m/s = frequency of the wave in Hz = wavelength of the wave in m v =
31. The wave moves on 10 m in 1 s, its speed is 10 m/s P the particle in the wave which makes 5 oscillations in 1 s P : wave motion P : P wave motion P wave motion the particle in the wave which makes oscillations in 1 s f wavelengths f 2 m 2 m 2 m 2 m 2 m P
32. = distance moved by wave in 1 s v = f ( m/s ) wave speed , v = distance moved by wave time taken to move = f metre 1 s
33. Q4 A vibrator dipped into water in a ripple tank has a frequency of 6 Hz. The resulting wave has a wavelength of 0.02 m. What is the speed of the wave?
34. Q5 A surf-board moves at 5 m/s on the crest of a wave. The distance between wave crests is 10 m. What is the frequency of the wave motion?
35. Displacement - position graph displacement position along wave direction (at a single moment in time, like a photograph)
36. displacement position along wave direction a = amplitude Wavelength and amplitude can be read from the graph. wavelength wavelength wavelength a a mean rest or position
38. displacement time Period and amplitude can be read from the graph. Frequency of the wave can be calculated from period read from the graph. f = 1/T a a period T period T period T mean rest or position
39. Q6 The diagram shows the outline of a water wave. 5 + 0.6 -0.6 15 25 0 displacement/cm displacement/cm What are the values of the amplitude and the wavelength? Amplitude
40. Q7 The diagram shows how displacement varies with time as a wave passes a fixed point. What is the frequency of this wave? time/s displacement/cm 0 1 3 2 4 0.05 0.1 -0.05 -0.1 period
41. Q8 The displacement-time graph of a wave travelling across water at a particular place with a velocity of 2 cm/s is shown in the diagram. What is the wavelength of the wave? 0.1 0.3 0.2 time/s 2 -2 displacement/mm 0 0.4 0.6 0.5 -1 1
42. Q9 A VHF radio station broadcasts at a frequency of 90 MHz (9.0 x 10 7 Hz). The speed of radio waves is 3.0 x 10 8 m/s What is the wavelength of the waves broadcast by the station?
43. Wavefront Pattern of Water waves Particles along the lines are moving in the same direction and at the same position in the wave. These lines are called wavefronts of the wave.
44. Wavefronts of water wave wave direction Wavefront is always perpendicular to the wave direction.
45. The Ripple Tank Ripple tank can be used to demonstrate reflection and refraction of wave. to battery and rheostat straight wave dipper Eccentric motor rubber band lamphouse water white screen
46. How is a wave pattern formed on screen? screen The distance between the two bright lines is the wavelength of the wave. bright line light
48. incident wavefronts reflected wavefronts reflector After reflection, there are no change of wavelength frequency and speed . There is a change of direction of waves. Wave energy decreases after reflection .
52. reflected wavefront S source I Centre of reflection reflecting surface Reflection of circular waves
53. reflected wavefront S source I Centre of reflection reflecting surface Construction of reflection of circular waves
54. S I Centre of reflection source reflecting surface P SP = IP Reflection of circular waves i = r Q R
55. Construction of reflection of circular waves 1 Draw a line from S perpendicular to the reflecting surface and extent the line. 2 Mark I on the line such that SP = P I . 3 Use I as a centre and I Q as a radius, draw an arc QR which is the reflected wavefront. 4 Repeat step 3 by increasing radius which is equal to ( I Q + wavelength).
56. S I Centre of reflection source reflecting surface reflected wavefront i r normal P r Reflection of circular waves reflected ray reflected ray
57. Refraction of Waves in Ripple Tank denser medium less dense deep water glass plate glass plate shallow water slow fast 1 2
58. From less dense medium to denser medium : wavelength and speed decreases From denser medium to less dense medium : wavelength and speed increases 2nd medium i r normal i 1st medium
60. Shallow water deep water refracted wave direction glass plate
61. When a wave travels from one medium to another medium with different densities. no change in frequency change in wave length and velocity.
62. Q10 A dipper moving up and down makes waves in a ripple tank. What will happen if the dipper frequency is increased? A The wave peaks will be higher and the troughs lower. B The waves will move more slowly across the tank. C The waves will move more quickly across the tank. D The waves will be closer together.
63. Refractive index Refractive index of a medium = c 1 = speed in 1st medium; c 2 = speed in 2nd medium c 1 / f 1 c 2 / f 2 f f 2 Refractive index of a medium = = 1 2 = c c 1 2 sin i sin r 1 2
64. From less dense medium to denser medium : wavelength and speed decreases From denser medium to less dense medium : wavelength and speed increases 2nd medium i r normal i 1st medium
65. Shallow water i r normal i deep water refracted wave direction
66. Construction of refracted wavefronts Angle of refraction is given. 1 Construct angle of refraction, r . 2 From the point of intersection of wavefront and the boundary, draw a line perpendicular to the reflected wave direction. 3 Repeat step 2 by using different points of intersection.
68. Q11 Which diagram below shows correctly how the water waves are refracted when they travel from the deep end to the shallow end? A B C D
69. Q12 The diagram shows a ripple tank with two different depths of water separated by a boundary XY. A wave generator is producing straight waves as indicated. The separation of the wave fronts is not drawn to scale, but the angles between the wave fronts and the barrier XY are as shown above. What is the ratio of the speed of the waves in deep water to their speed in shallow water? 35° 52° wave generator X Y
70. Facts about light 1 Light waves are transverse. 2 Light waves carry energy. 3 Light waves are emitted and absorbed by matter. 4 Light waves can travel through both vacuum and some matter. 5 Light waves travel at 3 x 10 8 m/s.
71. 6 Light waves can be reflected and refracted. 7 Light waves are part of electromagnetic spectrum. 8 Light also shows particle-like properties. 9 Light waves travel faster in less dens medium than that in denser medium.
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