WAVES
WAVES
Traveling disturbance
Transfer of energy
Two Wave Categories:
1) Electromagnetic Wave
2) Mechanical Wave - need a medium
Two Types of Mechanical Wave Motions:
1) transverse
2) longitudinal
pulse
WAVES
Periodic Waves
(repeats a pattern, or cycle)
amplitude
(Related to the energy content of a mechanical wave)
frequency
wavelength
v  f
period
WAVES
A sound wave traveling through air has a frequency
of 425 Hz and a wavelength of 0.800 meter. What is
the speed of this sound wave?
WAVE SPEED
depends on material properties of the medium
(constant in a given medium)
In a rope (or similar material), the speed of a wave is
determined by:
v
F
m
L
Tension in rope
Linear density of rope
kg 
 m 
WAVE SPEED
A transverse periodic wave is created in a rope of mass 2.00 kg
and length of 6.00 meters. The rope is under a tension of
150 N. The speed of the wave in the rope would be…
The wave cycles created in the rope have a period of
0.10 second. The wavelength of the “rope” wave
would be…
v  f  
T
You are in your car sitting at a red light
when you hear an ambulance siren. You
can not see the ambulance, yet you
know it is approaching you.
How can you tell the ambulance is
moving toward you?
The intensity DECREASES as the distance
from the source increases.
E
P
t
I 
A
A
The siren is producing sound energy at a
rate of 3.6 W, and you are 10.7 meters away
from the siren. What is the intensity of the
sound at your location?
If your eardrum has an area of 0.50 cm2, how
much energy passes through your eardrum in
a time of 5.0 seconds?
What would the intensity be at a distance of
1070 meters?
Wave Behaviors
Reflection
Changing direction upon meeting a barrier
(wave energy remains in original medium)
The polarity (orientation) of the wave may also be affected:
If the barrier is very rigid compared to the original
medium, the reflected wave will be inverted (have the
opposite polarity of incident wave).
If the barrier is very flexible compared to the original
medium, the reflected wave will be upright (have the
same polarity as incident wave).
Reflection
How much of the wave energy will reflect?
If barrier material is very similar to original medium, very
little of the wave energy will reflect. (Most will transmit
through to the new medium.)
If barrier material is very different from original
medium, most of the wave energy will reflect.
Reflection
Path of reflected wave is determined by the
Law of Reflection.
i   r
(measured relative to the normal line)
(transmitted portion not shown)
Refraction
changing direction when the wave enters
a new medium
Incident wave must make θ > 0˚ to normal line.
Caused by the wave changing speed when it enters
the new medium.
(Wave frequency remains the same.)
Which way will it bend?
If wave slows down, it bends toward the normal.
If wave speeds up, it bends away from the normal.
I have a BB machine gun, which emits a continuous
stream of metal BB’s. I point it at a metal plate that
has two openings in it and shoot.
If the metal plate is placed a certain distance in front of
a plaster wall, what will I see on the wall when I move
the plate away?
What if it is a beam of light instead?
Diffraction
bending around obstacles in its path,
changing direction as a result
The extent of the diffraction depends upon the
wavelength of the waves (λ) and the size of the
obstacle (d).
Generally:
diff. amt.  
d
Wave speed remains constant since medium doesn’t change.
Wave frequency also remains constant.
Interference
The effect on the medium when multiple waves meet
at the same location.
Principle of Linear Superposition – the resulting
disturbance is the sum of the individual wave
disturbances
constructive interference
destructive interference
circular wave interference(2D)
WAVES
Upon entering a new medium…
…what changes?
speed, wavelength, amplitude, possibly direction
…what remains the same?
FREQUENCY