1. Waves
Nature
Chaiporn Pattanajak
Banphue Pittayasan School

2. What are waves?

3. What are waves?
A wave is a phenomenon in which
energy is transferred through
vibration.

4. What are mechanical waves?
Mechanical waves are waves which require a
medium.
A medium is a form of matter through which the
wave travels (such as water, air, glass, etc.)
Waves such as light, x-rays, and other forms of
radiation do not require a medium.

5. Transverse Waves
In a transverse wave the matter in the wave moves
up and down at a right angle to the direction of the
wave.

6. Transverse Waves
 are waves which travel in a
direction perpendicular to the
direction of vibrations.
Direction of vibrations
Direction of wave

7. Longitudinal Waves (compression waves)
In a longitudinal wave the matter in the wave moves
back and forth parallel to the direction of the wave.

8. Longitudinal Waves (compression waves)
 are waves which travel in a direction
parallel to the direction of vibrations.
Direction of vibration
Direction of wave
examples include ssoouunndd wwaavveess

9. Characteristics of A Wave
 Crests and Troughs
 Amplitude
Wavelength
 Frequency
 Period
 Speed

10. Crests and Trough
Crests are high point of a wave
 Troughs are low point of a wave
displacement
distance
crest crest
ttrroouugghh

11. Check your understood
distance
displacement
A
G
F
E
D
C
B
I
H
O J
1. Which points of crests ?
2. Which points of troughs ?
Ans. A , E , I
Ans. C , G

12. Amplitude (A)
 is the height of a crest or depth of a trough
measured from the normal undisturbed
positions.
 is measured in metres (m)
displacement
distance
crest crest
Amplitude
Amplitude
trough

13. Wavelength (l)
 is the distance between two successive
crests or troughs
displacement
distance
ccrreesstt crest
Wavelength
Wavelength
trough trough
 is measured in metres (m)

14. Transverse waves
Longitudinal waves
wavelength

15. l
l
ssyymmbboollss ooff wwaavveelleennggtthh == l

16. Check your knowledge
distance
displacement
A
G
F
E
D
C
B
I
H
O J
Which pairs points are called wavelength? (true or false)
A ->C , B -> E , A -> E , D -> F , B -> F

17. frequency
 is the number of vibrations in one second
or frequency is the number of waves that
pass through a point in one second.
ssyymmbboollss ooff ffrreeqquueennccyy == ff
ff ==
n
t
Unit is waves per second
or Hertz (Hz).
nn == nnuummbbeerr ooff wwaavvee , tt == ttiimmee

18. Example
> 1 Hz = 1 wave per second.
t =1s
f wave 1
Hz
= 1 =
ond
1sec
> 50 Hz is 50 vibrations in 1 second.

19. Test Yourselves
 Explain the meaning of
 35 Hz,
 100 Hz ,

20. Wave Period (T)
 It is the time it takes for one cycle to complete.
 It also is the reciprocal of the frequency.
OO AA
AA
BB
CC
DD
aa ppeerriioodd iiss aa ttiimmee mmoovvee aarroouunndd cciirrccllee..
BB
CC
DD
AA
TT
aa ppaarrttiiccllee mmoovvee aarroouunndd
cciirrccllee.. ((ffiigg.. II)) T
2
((ffiigg.. IIII))
AA’’
AA’’

21. SI Unit For Period
 is measured in second (s)

22. Relationship between Period (T) and Frequency (f)
 f = 100 Hz Þ T = 1/100 s
 f = 40 Hz Þ T = 1/40 s
 f = 8 Hz Þ T = 1/8 s
f  f = f Hz Þ T 1
=
s ffrreeqquueennccyy iiss rreellaattee ppeerriioodd iinn eeqquuaattiioonn ::
T 1
f = Hz

24. Speed Of a Wave
 is the distance moved in one second.
Wave speed is usually measured in
meters/second, but may be
measured using other distance units
(such as centimeters per second).

25. Recall
 Speed of a motion
= distance ¸ time
V = s
t
where v = speed, s = distance and t = time
Distance of wave =
1
=
t
wavelength
frequency

26.  Speed of a wave
= wavelength ¸ period
= wavelength x frequency
V = lf
Wave Equation
where v = speed, f = frequency and l = wavelength

27. Example
A wave is traveling at a speed of 12 m/s and its
Wavelength is 3 m. Calculate the wave frequency.
Solution
1. This is what you know : speed (v) = 12 m/s , wavelength( l
) = 3m.
2. This is you want to find : wave frequency ( f )
3. This is the equation you need to use :
v = lf
4. Solve for f and then substitute
v
the known value in the equation.
f = l
f = 12 m / s = 4 (1/ ) =
4
x s Hz
m
3

28. Exam
ple The wave in figure are
traveling across water. Each wave
is 2m long, so that wavelength is
2m. One second later 3 wave have
passed the flag. Find wave speed.
SSoolluuttiioonn
11..TThhiiss iiss wwhhaatt ttoo
kknnooww
l
wwaavveelleennggtthh (( ))
== 22mm
wave
1sec
ond
3
FFrreeqquueennccyy ((ff))==
== 33 HHzz..
FFrroomm
v = lf
v = (2m)x(3Hz) = 6m/ s

29. PPrroobblleemm

30. Ques
tioThne in A below are traveling across water.
a) Are the wave transverse or longitudinal?
b) What is the wavelength of the wave?
c) What is the amplitude of the wave?
d) If 2 waves pass the flag every second, what is i) the
frequency ii) the period?
e) Use the wave equation to calculate the speed of wave
in A?
f) What is the wavelength of the wave in diagram B
bellow?
g) If the wave in B have the same speed as those in A,
what is their frequency and period?

31. 1. The diagram shows the outline of a water wave.
What are the values of the amplitude and the
wavelength?
amplitude / cm wavelength / cm
A 0.6 10
B 0.6 20
C 0.6 30
D 1.2 20 B

32. 2. Which wave is longitudinal ?
A light
B radio
C sound
D water
C

33. 3. The speed of 100 Hz wave was measured on four
different days. The results are shown in the table.
On which day the wave have the longest
wavelength ?
D
day speed of wave
A 315 ms-1
B 320 ms-1
C 335 ms-1
D 340 ms-1

34. 4. A source vibrates at frequency of 20 Hz and
produces waves of wavelength 0.02 m.
At which speed do these waves travel out from
the source ?
A 0.001 ms-1
B 0.021 ms-Hint:
1
v = lf
C 0.40 ms-1
D 20 ms-1 C

35. 5. A VHF radio station broadcasts at a frequency of
60MHz (6.0 x 107 Hz). The speed of radio
waves is 3.0 x 108ms-1.
What is the wavelength of the waves broadcast by
the station?
A 0.2 m
B 0.5 m
Hint:
C 2.0 m
v = lf
D 5.0 m D

36. Nov 1998
6. The diagram shows a coil spring along which a
longitudinal wave is moving.
(a) Mark on the diagram a distance equal to the
wave length of the wave. [1]
(b) Label on the diagram with the letter C where
the coils of the spring are compressed. [1]
C C
Wave length
C
(continue in next slide)

37. (Cont. …) Q 6
(c) Is the wave on the spring more like a sound wave
or a light wave? [1]
Sound wave, because sound wave is a longitudinal
wave but light wave is a transverse wave..

38. 7. The diagram below shows a transverse wave
travelling a rope.
wavelength
amplitude
(a) Mark on the diagram which is equal to (i)
the wavelength, (ii) the amplitude of the wave.
Label your answers. [2]
( b ) I f t h e w a v e l e n g t h i s 0 . 8 m a n d t h e f r e q u ency
is 2 Hz, what is the speed at which the wave
moves along the rope ? [2]
v = lf = 0.8 x 2 = 1.6 ms-1

39. Nov 1996
8(a) Explain the difference between a transverse
and a longitudinal wave. [2]
Transverse wave is a wave that its direction of
vibration is perpendicular to the direction of
propagation. It can travel through vacuum.
Longitudinal wave is a wave that its direction of
vibration is parallel to the direction of
propagation. It needs medium to travel.
(b) State one example of each type of wave.
Transverse
Light
Longitudinal Sound
[2]

40. GCE ‘O’ LEVEL Nov 1995
9.(a) Explain the difference between transverse and
longitudinal waves, referring in your answer to
the direction in which the waves travel. [2]
Transverse waves are waves that their direction
of vibration is perpendicular to their direction
of propagation.
Longitudinal waves are waves that their
direction of vibration is parallel to their
direction of propagation.
(continue on next slide)

41. 9.(b) The speed of sound in water is 1500m/s. What is a
wave length of a sound wave of frequency 250Hz
travelling through water ? [2]
Since v = lf
therefore 1500 = l 250
l = 1500 / 250 = 6.0 m
(Cont. …) Q. 9

42. 10. The diagram shows the air pressure at different
distances from a loudspeaker.
wavelength
amplitude
(a) Mark carefully on the diagram: [2]
(i) a distance which is the wavelength of the
(continue on next slide)
sound wave;
(ii) the amplitude of the sound waves.

43. 11 (b) If the wavelength of a sound wave of frequency
250 Hz is 1.4 m, calculate the speed of the wave.
[2]
(Cont. …) Q. 11
since v = lf
therefore, = 1.4 x 250
= 350 ms-1

44. 11(a) With the aid of a diagram, explain what is meant
by the frequency and wavelength of a wave. [5]
Frequency is the
number of vibrations
per second.
l
Wavelength is the distance from a point on a
wave to its next corresponding point.
It usually denote as l..
Longitudinal wave is a wave that its direction
of vibration always parallel to the direction of
propagation.
(b) What is a longitudinal wave ? [2]
(continue in next slide)