Phys 201
Waves
CH6 - Lecture 1
Dr.Haya Alhummiany
Objectives of the Lesson
• Understand the concept of wave motion in
the physical world
• Recall that there are two types of wave
motion- Longitudinal and Transverse
• Explain the difference between the types of
waves and use the correct terms for each
• State some examples of each of the types of
wave motion
Waves Introduction
• A wave can be described as a disturbance that
travels through a medium from one place to
another.
• Medium – a substance which something is
transmitted or carried through e.g.. air
• Wave Terms.
• Describing Vibrations.
• A cycle is the movement from some point, to another
point and back again.
• A period (T) is the time required for one complete
cycle.
• Frequency (f) is the number of cycles per second.
–Frequency is measured in Hertz (Hz)
–The period is the time for one cycle and the
frequency is the cycles per second, the
relationship is: T=1/f
»F = 1/T
• Wave Crest
– The maximum disturbance a wave will create from the resting
position
• Wave trough
– Maximum displacement a wave will create in the opposite
direction from the resting position.
• Amplitude
– The magnitude of the displacement to either the crest or the
trough.
• Wavelength
– The distance from one crest of a wave to the crest of the next
wave.
– Given the Greek symbol lambda ()
Here are some terms associated with periodic waves. The
wavelength is the distance from a part of one wave to the same
part in the next wave, such as from one crest to the next. The
amplitude is the displacement from the rest position. The
period is the time required for a wave to repeat itself, that is the
time for one complete wavelength to move past a given
location.
• Wave Equation
The wave equation tells us that the
relationship between speed, frequency,
and wavelength
• The speed of a wave equals the frequency times
the wavelength.
Frequency (cycles/sec)
Speed (m/sec)
v=f
Wavelength (m)
Example
• What is the speed of a water wave of
frequency 4 Hz and wavelength 3 cm?
v=fxλ
= 4 x (3 / 100)
= 0.12 m/s
Try this one…
What is the wavelength of a sound wave of frequency
264 Hz and speed 330 m/s?
v=fxλ
330 = 264 x λ
λ = 330 / 264 = 1.25 m
What is the distance between one compression and the
next rarefraction on this wave?
1.25 / 2 = 0.625 m
A graph of simple harmonic motion is described by a
sinusoidal curve.
Types of Waves- Transverse
Wave motion vs Particle motion
Watch one particle
Describe its motion
Moves up and down, while the wave passes from left to right.
Transverse wave…
Light travels as a transverse wave
Crest
Crest
Wavelength λ
Wave spreads
Amplitude
Wave movement
Trough
Trough
Wave movement is at right angles to
the direction that the wave is travelling
Amplitude –
maximum
displacement from
its undisturbed
position
Wavelength λ –
distance from one
point on one wave
to the same point
on the next wave
(for example- from
crest to crest)
In terms of the wavelength, what is the length of
the red line on the graph?
Types of Waves- Longitudinal
Wave motion vs Particle motion
Keep your eye on 1 particle
Describe its motion
Particles move back and forth on the same plane as the movement
of the wave
Longitudinal wave
Rarefaction
Compression
Sound waves
travel as
longitudinal
waves
Frequency – the
number of waves
passing a point
every second
(Hz)
Wave movement is parallel to the direction the wave is
travelling
If the diagram shows the motion of the wave in 1
second then what is the frequency of the wave?
Longitudinal Vs Transverse
• Create a table with two column headings,
Longitudinal and Transverse
This is how sound
energy moves
Wave motion is at
right angles to the
direction of the wave
Frequency is the
number of waves
passing a point in one
second
Wave motion is parallel to
the direction of the wave
Amplitude is maximum
displacement from the
wave’s rest position
Wavelength is the
distance from one
compression to the
next compression
Wavelength is the
distance from one
crest to the next
crest
This is how
light travels