Topic List
Types of Waves
Longitudinal Waves Transverse Waves Surface Waves
Frequency Wavelength Period
Amplitude
Wave speed Light Waves
Types of Waves
A mechanical wave is just a disturbance that propagate through a
medium. The medium could be air, water, a spring, the Earth, or even people. A medium is any material through which a wave travels.
Mechanical wave examples: sound; water waves; a pulse traveling on a spring; earthquakes; a “people wave” in a football stadium.
An electromagnetic wave is simply light of a visible or invisible wavelength. Oscillating intertwined electric and magnetic fields
Mechanical Waves: Three Types
Mechanical waves require a physical medium. The particles in the medium can move in two different ways: either perpendicual or parallel to direction of the wave itself.In a longitudinal wave, the particles in the medium move parallel to the direction of the wave.
In a transverse wave, the particles in the medium move perpen-dicular to the direction of the wave.
A surface wave is often a combination of the two. Particles typically move in circular or elliptical paths at the surface of a medium.
Longitudinal
Parallel
17 Waves –II P87 ;Par(2)
© 2014 John Wiley & Sons, Inc. All rights reserved.
fig(a)
fig(b)
Compression &Rarefaction Longitudinal wave
transverse wave
Surface Waves
Surface waves are both transverse waves and longitudinal waves mixed in one medium.
Animation
Wave Characteristics
Amplitude (A) – Maximum displacement of particle of the medium from its equilibrium point. The bigger the amplitude, the more energy the wave carries.
Wavelength () – Distance from crest (max positive displacement) to crest; same as distance from trough (max negative displacement) to trough.
Period (T) – Time it takes consecutive crests (or troughs) to pass a
given point, i.e., the time required for one full cycle of the wave to pass by. Period is the reciprocal of frequency: T = 1/f.
Frequency (f) – The number of cycles passing by in a given time. The SI unit for frequency is the Hertz (Hz), which is one cycle per second.
Wave speed (v) – How fast the wave is moving (the disturbance itself, not how fast the individual particles are moving, which constantly
Displacement vs position
Position X(cm)
D
is
p
la
ce
m
en
t
s(
x,
t) Amplitude (sm) Wavelength ()
3.Describing sound waves (expansions and compressions)
Frequency
&
Period
Period = seconds per cycle.
Frequency = cycles per second
.If a sound wave that has a frequency of 1,000 Hz
has a period of
1 / 1,000 of a second.
Example:
A radio wave has a frequency of 93.9 MHz (93.9 * 10
6Hz). What is its period?
f = 93.9 * 10
6Hz
f = 1 / T
T = 1 / f
T = 1 / 93.9 x 10
6Hz
Speed, Wavelength,
&
Frequency
v =
f
f
v
m
x
x
f
v
395
10
760
10
3
3 8
Example (1):
If a frequency of 760 kHz is emitted with radio velocity
in the order of 3x10
8m/sec, calculate the wavelength?
Solution:
Note that:
f = 760 kHz = 760x10
3Hz
v= 3x10
8m/sec
But, as known:
Example (1):
If a frequency of 760 kHz is emitted with radio velocity
in the order of 3x10
8m/sec, calculate the wavelength?
Solution:
Note that:
f = 760 kHz = 760x10
3Hz
v= 3x10
8m/sec
Light Waves
Light Waves
light behaves as both a wave and as a particle
light behaves as both a wave and as a particle
.
.
Light requires no medium!Light requires no medium!
It can travel through space that contains matter (such as It can travel through space that contains matter (such as air, glass, or water) or through a vacuum.
air, glass, or water) or through a vacuum.
Light spreads out in all directions from its source. Light travels in straight lines called rays
Light travels at the “speed of light”
299,792 kilometers per second
=(300,000,000 meters/second)
Electromagnetic Spectrum
– Long wavelength-lowest frequency – Short wavelength highest frequency – The higher the frequency the higher the
RADIO WAVES
• Have the longest wavelengths and lowest
frequencies of all the electromagnetic waves.
1-Global Positioning Systems (GPS).
2-A radio picks up radio waves
through an antenna and converts it to
sound waves.
3-MRI
(MAGNETIC RESONACE
IMAGING)
Uses Short wave radio waves with
Used in microwave
ovens.
• Waves transfer
energy to the
water in the food
causing them to
vibrate which in
turn transfers
INFRARED RAYS
• Infrared= below red• Shorter wavelength and higher frequency than microwaves.
Thermogram—a picture that shows regions of different
ULTRAVIOLET RAYS
• Shorter wavelength and higher frequency
than visible light
• Carry
more energy
than visible light
• Used to
kill bacteria.
• Too much can cause skin cancer.
• Use sun block to protect against (UV rays)
• Causes your skin to produce
vitamin D
X- RAYS
• Shorter wavelength and higher frequency
than UV-rays
• Carry a great amount of energy
• Can penetrate most matter.
Bones and teeth absorb x-rays. (The light part of an x-ray image
indicates a place where the x-ray was absorbed)
The most common form of X-ray used is X-X-ray radiography, which can be used to help
GAMMA RAYS
• Shorter wavelength and higher frequency than
X-rays
• Carry the greatest amount of energy and
penetrate the most.
• Used in radiation treatment to kill cancer
cells.
