Fizik bab 6.1 Gelombang - SPM

1. Chapter 1: Waves
1.1 Understanding Waves

2. Motion of Waves
• 1 An oscillating or vibrating motion in which
a point or body moves back and forth along a
line about a fixed central point produces
waves.

3. Motion of Waves
• 2. Examples of waves:
• (a) Light waves are produced as a result
of vibrations of electrons in an atom.

4. Motion of Waves
• 2. Examples of waves:
• (b)Sound waves are produced by
vibrating mechanical bodies such as
guitar strings or a tuning fork.

5. Motion of Waves
• 2. Examples of waves:
• (c) Water waves are produced by
disturbance (or vibration) on a still water
surface.

6. Propagation (Traveling) of Waves
• 1.When a wave travels through a
medium, the particles of the medium
vibrate about their equilibrium
positions.
Direction of
waves

7. Propagation (Traveling) of Waves
• 2.However, the particles of the medium
do not travel in the direction of the
wave.

8. Propagation (Traveling) of Waves
• 3 A wave transfers energy and the
momentum from the source of the wave
(the oscillating or vibrating system) to the
surroundings.

9. Propagation (Traveling) of Waves
• Activity 1.1: To demonstrate that waves transfer
energy without transferring matter
• Apparatus:
• Radio, candle and matches.

10. Propagation (Traveling) of Waves
• Activity 1.1: To demonstrate that waves
transfer energy without transferring matter
• Procedure
• 1. A candle is placed about 10 cm from the
speaker of a radio.

11. Propagation (Traveling) of Waves
• Procedure
• 2. The candle is lit and the movements of its
flame is observed.

12. Propagation (Traveling) of Waves
• Procedure
• 3. Then, the radio is turned on and the volume
of the sound is gradually increased until a
change in the movement of the flame becomes
noticeable.

13. Propagation (Traveling) of Waves
• Discussion
• 1. The flame vibrates when the radio is
turned on.

14. Propagation (Traveling) of Waves
• Discussion
• 2. This observation shows that the
propagation of the sound waves from the
vibration of the cone of the speaker
transfers energy (or momentum) to the
flame and causes it to vibrate.

15. Propagation (Traveling) of Waves
• Conclusion
• Waves transfer energy from a vibrating
system without transferring matter.

16. Wavefronts
• 1. A wave front is a line or plane on
which the vibrations of every points on it
are in phase and are at the same
distance from the source of the wave.
Same
Phase

18. Wavefronts
• 2 . Points in a wave are in phase if they
vibrate in the same direction with the
same displacement.
Same
displacement

19. Plane Wave fronts
• 1 . Figure 1.3 shows the production of
plane water waves when a wooden bar
vibrates vertically at a constant frequency
on the surface of the water.

20. Plane Wave fronts
• 2. Lines PQ, RS, TU and VW are straight
lines along the respective crests of the
waves. These lines are called wave
fronts.

21. Circular Wave fronts
• 1. When we use a fingertip to touch the
surface of water repeatedly, circular wave
fronts are produced as shown in Figure
1.4.

22. Types of Waves
• There are two types of waves.
• (a) Transverse wave
• (b) Longitudinal wave

23. Transverse Waves
• 1. A transverse wave is a wave in which
the vibration of particles in the medium is
at right angle (perpendicular) to the
direction of propagation of the wave.

24. Transverse Waves
• 2. A model of a transverse wave can be
produced by a slinky spring as shown in
Figure 1.6.

25. Transverse Waves
• 3. Examples of transverse waves are
water waves and light waves.

26. Longitudinal Waves
• 1. A longitudinal wave is a wave in which
the vibration of particles in the medium is
parallel to the direction of propagation of
the wave.

27. Longitudinal Waves
• 2. When the slinky spring is vibrated back
and forth along the direction of
propagation of the wave at a fixed rate, a
longitudinal wave is produced as shown in
Figure 1.8.

28. Longitudinal Waves
• 3 . Example of longitudinal waves is
sound waves.

29. Amplitude, Period and Frequency of a Wave
• 1 . The amplitude, A, of a vibrating system is
maximum displacement from its equilibrium position.
It is a measure of height of the wave crest or depth of the
wave trough.
Amplitude

30. Amplitude, Period and Frequency of a Wave
• 2 . In Figures 1.9 (a) and (b), the distance OQ is the
amplitude, where O is the equilibrium position of the
vibrating system.
Amplitude

31. Amplitude, Period and Frequency of a Wave
• 3 . The period, T, of a vibrating system is the time
taken to complete an oscillation.
Period

32. Amplitude, Period and Frequency of a Wave
• 4. In the two vibrating (oscillating) systems show in
Figure 1.9, a complete oscillation are:
• (a) from P  Q  P or Q  P Q,
• (b) from OPQO or
OQPO

33. Amplitude, Period and Frequency of a Wave
• 5. If a vibrating system makes n complete
oscillations in a time of t seconds, the
period of oscillation, T of the system is
second
• The SI unit of period is second.
n
t

34. Amplitude, Period and Frequency
of a Wave
• 6 The frequency, f, is the number of complete
oscillations made by a vibrating system in one second.
• The unit of frequency is hertz (Hz) or s-1.

35. Amplitude, Period and Frequency
of a Wave
• 7 From the formulae of T and f, the relationship
between period, T and frequency, f is:
• T is inversely proportional to f and vice versa.

36. Amplitude, Period and Frequency
of a Wave
• Example 1:
• In an experiment, Aziz observes that a simple pendulum
completes 30 oscillations in 48.0 seconds. What is
• (a) the period of oscillation?
• (b) the frequency of oscillation?

37. Amplitude, Period and Frequency
of a Wave
• Example 1:
• Solution
• (a)
s6.1
30
48.0
oscllationcompletedofnumber
takentime
Tperiod,



38. Amplitude, Period and Frequency
of a Wave
• Example 1:
• Solution
• (b)
Hz625.0
6.1
1
T
1
ffrequency, 

39. Displacement-time Graph of a
Wave
• 1. The sinusoidal graph in Figure 1.10 is a
graph of displacement, s against time, t of
a load on a spring.

40. Displacement-time Graph of a
Wave
• 2 From the graph of s against t in Figure 1.10, the
following information is obtained.
• (a) Amplitude, A = a cm
• (b) Period of oscillation, T is the time between points:
• (i) O and F, (ii) C and G or (iii) P and Q.

41. Displacement-time Graph of a
Wave
• Example 2:
• Figure 1.11 shows the displacement-time graph of the
oscillation of a mass on a spring.
• Figure 1.11

42. Displacement-time Graph of a
Wave
• Example 2:
• From the graph,
• (a) state the amplitude,
• (b) calculate the period of the oscillation,
• (c) calculate the frequency of the oscillation.

43. Displacement-time Graph of a
Wave
• Example 2:
• Solution
• (a) Amplitude, A = 5 cm
•

44. • Example 2:
• Solution
• (b) Period of oscillation, T = 0.04 s

45. • Example 2:
• Solution
• (c) Frequency of oscillation,
Hz
T
f 25
04.0
11


46. Displacement-distance Graph of a
Wave
• 1. Figures 1.12 (a) and (b) show the
propagation of a water wave and a sound
wave.

47. Displacement-distance Graph of a
Wave
R: Rarefaction
C:Compression

48. Displacement-distance Graph of a
Wave
• 2. The displacement, s of each particle of the medium
at different distances can be shown in a displacement-
distance graph as shown in Figure 1.12 (c).

49. Displacement-distance Graph of a
Wave
• 3. The wavelength, , is the distance between
successive points of the same phase in a wave.

50. Displacement-distance Graph of a
Wave
• For example:
• (a) the distance between two successive crests or two
successive troughs in a water wave,

51. Displacement-distance Graph of a
Wave
• (b) the distance between two successive compressions
or two successive rarefactions in a sound wave.
The SI unit of wavelength,  , is metre (m).

52. Displacement-distance Graph of a
Wave
• Example 3:
• Figure 1.13 shows a displacement-distance
graph of a wave.
• Figure 1.13
• Find
• (a) the amplitude,
• (b) the wavelength of the wave.

53. Displacement-distance Graph of a
Wave
• Example 3:
• Solution
• (a) Amplitude, A = 4 cm
•

54. Displacement-distance Graph of a
Wave
• Example 3:
• Solution
• (b) Wavelength, =12 cm

55. Relationship between Speed (v),
wavelength,  and Frequency (f)
• The relationship between speed,
wavelength and frequency can be
obtained by relating the SI unit of the
quantities.
fv 

56. Relationship between Speed (v),
wavelength,  and Frequency (f)
• Example 4:
• A wave of frequency 120 Hz has a
wavelength of 5.0 m. What is the speed of
the wave?

57. Relationship between Speed (v),
wavelength,  and Frequency (f)
• Example 4:
• A wave of frequency 120 Hz has a
wavelength of 5.0 m. What is the speed of
the wave?
Solution
f = 120 Hz and  =5.0m
Speed of wave,
v = f 
= 120 x 5
= 600 m s-1

58. Relationship between Speed (v),
wavelength,  and Frequency (f)
• Example 5:
• The displacement-distance graph in Figure
1.14 shows the motion of a transverse
wave. The source of the wave produces
10 complete waves in one second.
• Figure 1.14

59. Relationship between Speed (v), wavelength, 
and Frequency (f)
• Example 5:
• Calculate
• (a) the amplitude,
• (b) the wavelength, and
• (c) the speed of the wave.

60. Relationship between Speed (v),
wavelength,  and Frequency (f)
• Example 5:
• Solution
• (a) Amplitude, A = 6 cm
•

61. Relationship between Speed (v),
wavelength,  and Frequency (f)
• Example 5:
• Solution
• (b) Wavelength, = 20 cm
•
•
•

1o 2o

62. Relationship between Speed (v),
wavelength,  and Frequency (f)
• Example 5:
• Solution
• (c) Frequency, f = 10 Hz, = 20 cm
• Speed, v = f
=10x20
• = 200 cm s-1

