Waves
S Caesar
Physics
Objectives
• In this PowerPoint the students will learn:
• The properties of a wave
• Behavior of Waves
• Differentiate elastic & electromagnetic
•
waves
How to calculate the period, frequency,
and wave length of a wave.
STANDARDS –SP4
• SP4
• Description: SP4 Students will analyze the
properties and applications of waves.
• Elements:
a. Explain the processes that results in the
production and energy transfer of
electromagnetic waves.
Mechanical Waves
A mechanical wave is a physical
disturbance in an elastic medium.
Consider a stone dropped into a lake.
Energy is transferred from stone to floating log, but only the
disturbance travels.
Actual motion of any individual water particle is small.
Energy propagation via such a disturbance is known as
mechanical wave motion.
What are electromagnetic waves?
• How electromagnetic waves are formed
• How electric charges produce
electromagnetic waves
• Properties of electromagnetic waves
Electromagnetic Waves…
• Do not need matter to transfer energy.
• Are made by vibrating electric charges and
can travel through space by transferring
energy between vibrating electric and
magnetic fields.
This page was copied from Nick Strobel's Astronomy Notes. Go
to his site at www.astronomynotes.com for the updated and
corrected version.
Making Electromagnetic Waves
• The electric and magnetic fields vibrate at right
angles to the direction the wave travels so it is a
transverse wave.
Electromagnetic Waves
These waves do not need
matter to travel.
Difference between the
different waves is wave
length
EM spectrum illustrates the
differences
Electromagnetic Waves
How they are formed
Kind of wave
Sometimes behave as
Electromagnetic Waves
How they are
formed
Waves made by
vibrating electric
and magnetic
fields cthat can
travel through
space where there
is no matter
Kind of wave
Sometimes behave as
Transverse
with
alternating
electric and
magnetic
fields
Waves or as
Particles
(photons)
WAVES
• How are mechanical( elastic) waves
different from electromagnetic waves ?
• Differentiate them in terms of definition,
their properties, examples
Mechanical Wave
Differentiate
Elastic
• Example:
– Water waves
– Sound waves
– Waves on a spring or string
• Mechanical (Elastic) waves
need a medium to travel
• Mechanical waves transport
energy and not material
Electromagnetic
• Example
– Microwave
– X-ray, Gamma ray
– Light waves, UV rays
• Do not need a medium to
travel
• It travels with very high
speed
• Can be described by their
wavelength, energy, and
frequency
Cont’d
• Requires initial energy
input be created
• Mechanical waves cause
displacement of the matter
through which the wave is
traveling
• Mechanical waves
vibrations can put air
molecules in motion
• Very low energy and
frequency
• Big wavelength
• Remember that energy
gets transferred and not
materials
• Electromagnetic waves
cause no displacement of
matter and can transfer
energy in the absence of
matter
• Do not need to take place
in any media vibrations
• Very high energy and high
frequency
• Electromagnetic vibrations
do not put our molecules in
motion
Types of Waves
Mechanical Waves
• A wave is a method of
•
•
transferring energy from
one place to another
without transferring
matter.
Mechanical waves are
those that require a
medium for their transfer
and include
water waves, sound
waves and waves in
stretched strings.
Electromagnetic Waves
• Electromagnetic waves
consist of varying electric
and magnetic fields.
• The two fields are
perpendicular to each
other and to the direction
of travel of the wave.
• Each vibrates with high
frequency -
Objectives
• In this PowerPoint the students will learn:
• Demonstrate your understanding of transverse
•
•
and longitudinal waves.
Define, relate and apply the concepts of
frequency, wavelength, and wave speed.
Solve problems related to them.
A Transverse Wave
In a transverse wave, the vibration
of the individual particles of the
medium is perpendicular to the
direction of wave propagation.
Motion of
particles
Motion of
wave
Longitudinal Waves
In a longitudinal wave, the
vibration of the individual
particles is parallel to the
direction of wave propagation.
v
Motion of
particles
Motion of
wave
Production of a Longitudinal Wave
l
l
• An oscillating pendulum produces
condensations and rarefactions that travel
down the spring.
• The wave length l is the distance
between adjacent condensations or
rarefactions.
Sound
• Sound is produced when an
object vibrates.
• When an object vibrates it exerts
a force on the surrounding
• Sound is a mechanical wave
(requires a medium to travel and
they are compression wave
(molecules colliding).
• The medium sound travels
through are of Air.
• Loudness of a sound is recorded
in decibels
• As a sound gets louder, the
amplitude of the wave increases
Water Waves
An ocean wave is a combination of transverse and
longitudinal.
The individual
particles move in
ellipses as the wave
disturbance moves
toward the shore.
What is a wave?
• A wave is a disturbance which moves
through a medium.
• Water waves and sound waves are
examples of mechanical waves.
• Light waves are not considered mechanical
waves. They are electromagnetic in
nature.
What is an amplitude?
Amplitude: the height of the wave,
measured in meters.
What are frequency waves?
Frequency: the number of complete waves that pass a point in one second,
measured in inverse seconds, or Hertz (Hz).
What are transverse waves?
Speed: the horizontal speed of a point on a wave as it propagates, measured in meters
/ second.
Speed of wave, v = frequency
Terminology
• Amplitude: Height of Wave (m)
• Wave Length: distance from one wave top, or
crest, to the immediate next. (m)
• Phase Shift: how far to the left or right the wave
slides. (m)
• Frequency: refers to how many waves are made
per time interval. This is usually described as how
many waves are made per second, or as cycles
per second. (hz)
Crest: top most part of the wave
Trough: bottom most part of the wave
Period: the time needed to repeat one complete
cycle of motion.
Transverse Waves (cont.)
Frequency and Wavelength
As frequency increases wavelength decreases
As frequency decreases wavelength increases
What is wavelength?
Wavelength: the distance between
adjacent crests, measured in meters.
Velocity and Wave Frequency.
The period T is the time to move a
distance of one wavelength. Therefore,
the wave speed is:
l
1
v
but T 
so v  f l
T
f
The frequency f is in s-1 or hertz
(Hz).
The velocity of any wave is the product of
the frequency and the wavelength:
v fl
Problem #1
• What is the speed of a periodic wave
disturbance that has a frequency of 3.5 Hz
and a wavelength of 0.7 m?
• Given f= 3.5 Hz &
• V= f x
• V=
Problem #1
• What is the speed of a periodic wave
disturbance that has a frequency of 3.5 Hz
and a wavelength of 0.7 m?
• V= f x
• V= 3.5 x 0.7= 2.45 m/s
Example 2: An electromagnetic vibrator
sends waves down a string. The vibrator
makes 600 complete cycles in 5 s. For one
complete vibration, the wave moves a
distance of 20 cm. What are the frequency,
wavelength, and velocity of the wave?
600 cycles
f 
;
5s
f = 120 Hz
The distance moved during a time of
one cycle is the wavelength;
therefore:
l = 0.020 m
v = fl
v = (120 Hz)(0.02 m)
v = 2.40 m/s
Problem #2
• An ocean wave has a length of 12.0 m. A
wave passes a fixed location every 3.0 s.
What is the speed of the wave?
• Given d= 12.0 m
•
t= 3.0 s
• v= d / t
• v= (12/3)= 4.0 m/s
Problem #2
• An ocean wave has a length of 155.0 m. A
wave passes a fixed location every 9.0 s.
What is the speed of the wave?
• v= d / t
• V=